Séminaires du LIPN
Depuis 2007, plus de 1361 séminaires ont été présentés dans le laboratoire

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Séminaires à venir
SAFER 18/06/2026 Titre bientôt dispThe Dynamic Turn in Strategy Logics: On Individual and Group Abilitiesonible, par Rustam Galimullin
Rustam Galimullin, University of Bergen  
Salle Y403, Université de Villetaneuse
18/06/2026    14:00 - 15:00
Résumé :
I will introduce the research agenda of ‘dynamifying’ logics for strategic reasoning (or, strategy logics) like Coalition Logic and Alternating-Time Temporal Logic by extending them with model-transforming modalities. This endeavour is inspired by the success of Dynamic Epistemic Logic (DEL), which allow one to reason about the effects of various types of private and public communication on agents’ knowledge and beliefs. Needless to say, models of DEL and strategy logics are quite different and capture different aspects of multi-agent systems. However, I will pose that intuitions from DEL can be useful in defining interesting model transformations for strategy logics. As a specific example, I will present one of our earlier papers on extending strategy logics with model-transforming modalities that correspond to granting and revoking abilities for agents. I will then discuss some limitations of the framework, as well as some further results. As an ultimate informal goal of this research agenda I envision the collaboration between researchers in DEL and strategy logic, as, I believe, they have a lot to offer to each other.
SAFER 18/06/2026 Titre bientôMotivation and Background Reachability Graph Analysis Optimal Deadlock Control of Automated Manufacturing Systems Using Petri Nets: A Reachability Graph Approacht disponible, par Zhiwu Li
Zhiwu Li, School of Electro-Mechanical Engineering Xidian University  
Salle Y403, LIPN, Université de Villetaneuse
18/06/2026    15:00 - 16:00
Résumé :
For the deadlock problem in automated manufacturing systems, a deadlock prevention and control method based on Petri net reachability graph analysis is introduced. The reachability graph of a Petri net model is dichotomized into legal and deadlock zones; the concept of first-met bad markings is proposed. The use of vector covering effectively reduces the number of constraints and variables of the linear programming problems formulated for an optimal controller design, making the reported methods applicable to large-scale systems. Finally, the idea of ??vector covering is applied to general Petri net models to solve the supervision and control problem of unstructured net systems.
LOCAL 02/07/2026 Programming language and formally verified compiler for low-level numerical libraries, par Josué Moreau
Josué Moreau, Inria Saclay, LMF  
Salle B107, bâtiment B, Université de Villetaneuse
02/07/2026    10:30 - 12:00
Résumé :
Low-level numerical libraries like GMP and BLAS are widely used. They are mostly written in C, Fortran, and Assembly, and make a heavy use of arrays and pointers. These languages are well-suited for writing efficient code but they are not safe, that is, they have many undefined behaviors, which increase the chance for bugs. Moreover, their semantics make it difficult to reason about programs, and therefore to verify them; this is however a critical point because the correctness of numerical libraries is often subtle. Finally, the compilers for these languages are often very optimizing and thus very complex, which might reduce the confidence in the code they generate. This work focuses on the design of a language, named Capla, and of its compiler. They address the aforementioned issues, while being well-suited to writing and verifying efficient low-level numerical libraries. In particular, the semantics of Capla, along with the proofs of type safety and of compiler correctness, have been formalized using the Rocq proof assistant.
Séminaires passés
LOCAL 11/06/2026 Relational extensions, par Quentin Aristote
Quentin Aristote, IRIF  
Salle B107, bâtiment B, Université de Villetaneuse
11/06/2026    10:30 - 12:00
Résumé :
In 1970, Barr characterized which Set-functors and natural transformations extend to the locally posetal category of sets and relations. His goal was to then describe topological spaces as certain "relational algebras", but his result also proved relevant for the study of linear logic (through its weighted relational model), transition systems (through coalgebras) and effectful programming (through distributive laws). In this talk I will review the main idea behind Barr's characterization --- seeing relations as spans --- and how it has been adapted to more general settings. I will focus on two of my own results: a characterization of extensions to the Kleisli categories of powerset-like monads, with the aim of building weak distributive laws involving non-determinism, and, as jww. Umberto Tarantino, a characterization of extensions to the bicategory of profunctors, with the aim of adapting Barr's description of topological spaces to the 2-dimensional setting.
CALIN 09/06/2026 Flip graphs of triangulations on polygons, par Zili Wang
Zili Wang, Dartmouth College, Department of Mathematics  
Salle B107, bâtiment B, Université de Villetaneuse
09/06/2026    14:00 - 16:00
Résumé :
Given a set of points on the plane, one can consider the set of triangulations using these points as vertices. Two triangulations are related by a flip if they differ by an edge. Flips are important in both mathematics and computer science, such as optimizing triangulations, computing geodesics and studying the mapping class groups on surfaces. An interesting but difficult question is computing the flip distance between two triangulations of a given set of points. Our work focuses on the specific case when the points are the vertices of a planar polygon. In this context, it is well known that computing flip distances is closely related to decomposing some three-dimensional polyhedron into tetrahedra. In this talk, we will explain this relationship, and present our results following this perspective. This talk is based on joint work with Lionel Pournin and Peter Doyle.
LOCAL 03/06/2026 Harmony in Rocq, par Sergueï Lenglet
Sergueï Lenglet, LIPN, Equipe Molotov  
Salle Tour Eiffel Y403
03/06/2026    14:00 - 15:00
Résumé :
The POPLmark challenge has been a source of progress for the representation of binders in proof assistants for sequential calculi. In the same spirit, the Concurrent Calculi Formalization Benchmark proposes a set of challenges covering issues with the representation of concurrent systems models such as process algebra. One of them is about scope extrusion, i.e., the dynamic extension of the scope of a binder during reduction. The benchmark proposes to formalize the harmony lemma, a correspondence result between two semantics of a minimal $\pi$-calculus. We present an answer to this challenge in Rocq using de Bruijn indices and the library Autosubst. Our goal is to assess how this library, developed for sequential languages, helps in a concurrent setting.
CALIN 26/05/2026 A Combinatorial Framework for the Pons-Batle Identity: Young Tableaux, Lattice Paths, and Limit Laws, par Michael Wallner
Michael Wallner, Institute of Discrete Mathematics and Geometry, TU Wien  
Salle B107, bâtiment B, Université de Villetaneuse
26/05/2026    14:00 - 16:00
Résumé :
The Pons-Batle identity asserts an intriguing link between a particular class of words of length n and the set of tree-child networks with n nodes. Although a recent fully computational proof confirmed its validity, a combinatorial interpretation remains an intriguing open problem. In this talk, we focus on the rich combinatorial and asymptotic structures underlying these objects. First, we examine the structural properties of the conjecture by establishing a correspondence between these networks and two distinct families of Young tableaux with walls. This correspondence enables us to derive a trivariate linear recurrence with polynomial weights that has a natural interpretation in terms of two special families of Dyck paths with space-dependent steps. Using differential operators, we derive explicit bivariate algebraic generating functions that encode the length and the number of reticulation nodes. Using a recursive algorithm based on this approach, we provide an alternative proof of the conjecture for all families with up to 250 reticulations. Finally, we move from exact enumeration to asymptotic analysis. Extracting the asymptotic behavior from these generating functions reveals the underlying probabilistic structures of these networks, which are characterized by beta and uniform limit distributions.
CALIN 21/05/2026 Diagonals and Hadamard Products of D-finite Power Series, par Shaoshi Chen
Shaoshi Chen, Academy of Mathematics and System Sciences, Chinese Academy of Sciences  
Salle B107, bâtiment B, Université de Villetaneuse
21/05/2026    14:00 - 15:00
Résumé :
D-finite power series appear ubiquitously in combinatorics, number theory, and mathematical physics. They satisfy systems of linear partial differential equations whose solution spaces are finite-dimensional, which makes them enjoy a lot of nice closure properties. In particular, the diagonals and Hadamard products of D-finite power series are still D-finite. The first part of this talk will present a proof of the diagonal theorem following an idea of Gessel and also provide a single exponential bound on the degree and order of the defining differential equation satisfied by the diagonal (based on a joint work with Frederic Chyzak, Pingchuan Ma and Chaochao Zhu). The second part of this talk is about the arithmetic properties of Hadamard products of D-finite power series (based on a joint work with Ruyong Feng, Manuel Kauers, Michael Singer and Umberto Zannier).
AOC 21/05/2026 Integer programs with bounded subdeterminants: solving structured cases, par Stefan Kober
Stefan Kober  
Salle B107, bâtiment B, Université de Villetaneuse
21/05/2026    10:30 - 12:00
Résumé :
It is a notorious open question whether integer programs (IPs), with an integer constraint matrix M whose subdeterminants are all bounded by a constant in absolute value, can be solved in polynomial time. We give an overview on recent progress towards this question and the rich combinatorial structures hidden within. Further, we show how to solve such IPs if the constraint matrix fulfills certain further structural conditions. This talk is based on the following papers: Aprile, M., Fiorini, S., Joret, G., Kober, S., Seweryn, M. T., Weltge, S., & Yuditsky, Y. Integer programs with nearly totally unimodular matrices: the cographic case. [SODA 2025] Fiorini, S., Kober, S., Seweryn, M. T., Shantanam, A., & Yuditsky, Y. Face covers and rooted minors in bounded genus graphs. [preprint 2025] Kober, S. Totally ?-Modular IPs with Two Non-zeros in Most Rows. [IPCO 2025]
LOCAL 21/05/2026 Groups and inverse semigroups in lambda calculus , par Arturo De Faveri
Arturo De Faveri, IRIF  
Salle Tour Eiffel Y403
21/05/2026    10:30 - 12:00
Résumé :
We study invertibility of ?-terms modulo ?-theories. Here a fundamental role is played by a class of ?-terms called finite hereditary permutations (FHP) and by their infinite generalisations (HP). More precisely, FHPs are the invertible elements in the least extensional ?-theory ?? and HPs are those in the greatest sensible ?-theory H*. Our approach is based on inverse semigroups, algebraic structures that generalise groups and semilattices. We show that FHP modulo a ?-theory T is always an inverse semigroup and that HP modulo T is an inverse semigroup whenever T contains the theory of Böhm trees. An inverse semigroup comes equipped with a natural order. We prove that the natural order corresponds to ?-expansion in FHP/T, and to infinite ?-expansion in HP/T. Building on these correspondences we obtain the two main contributions of this work: firstly, we recast in a broader framework the results cited at the beginning; secondly, we prove that the FHPs are the invertible ?-terms in all the ?-theories lying between ?? and H+. The latter is Morris' observational ?-theory, defined by using the ?-normal forms as observables. This is joint work with Bucciarelli, Manzonetto, Salibra and will appear in the Proceedings of FSCD 2026.
CALIN 19/05/2026 Singularly perturbed DDEs and pattern counts in triangulations, par Eva-Maria Hainzl
Eva-Maria Hainzl, LIX, École Polytechnique  
Salle B107, bâtiment B, Université de Villetaneuse
19/05/2026    14:00 - 16:00
Résumé :
Discrete differential equations (DDEs), also known as catalytic equations, appear in the enumeration of several combinatorial classes, such as planar maps, parking trees and many more. We consider this type of equation for generating functions enriched with an additional variable $x$, where the order of the equation is $1$ for $x=0$ but $k> 1$ for $x\ne 0$. We show that, under certain assumptions, there is a smooth transition in the singular behavior of the generating function when varying $x$. As an application of this result we consider pattern counts in planar triangulations and derive a central limit theorem for these counts.
CALIN 12/05/2026 La hauteur de l'arbre des infections, par Delphin Sénizergues
Delphin Sénizergues, MODAL'X, Université Paris Nanterre  
Salle B107, bâtiment B, Université de Villetaneuse
12/05/2026    14:00 - 16:00
Résumé :
On considère un modèle d'épidémie SIR (Susceptible-Infected-Removed) démarré avec un individu infecté dans une population contenant un grand nombre $n$ d'individus sains. Chaque individu guérit à taux $1$ et infecte chaque individu sain à taux $\lambda_n$. On encode tous les événements d'infection ayant eu lieu au cours de l'épidémie dans un arbre T_n. On s'intéresse à la hauteur de cet "arbre des infections" T_n, en particulier dans le régime $\lambda_n = \lambda / n$ pour $\lambda$ une constante plus grande que $1$, qui demande une analyse particulière. La hauteur asymptotique de l'arbre dans ce régime fait apparaître une transition de phase en $\lambda$ autour d'une valeur $\lambda_c\approx 1.80$. J'expliquerai les grandes étapes de la preuve et présenterai quelques outils qui permettent d'analyser le modèle: un lien avec les arbres récursifs gelés, ainsi que le contrôle précis du profil de ces arbres grâce à une famille de martingales.
AOC 07/05/2026 Optimizing Networks Across the Device-Edge-Cloud Continuum, par Alberto Ceselli
Alberto Ceselli  
Bâtiment Hypatia, "Salle Tour Eiffel", étage 4
07/05/2026    10:30 - 12:00
Résumé :
Modern networked systems are no longer confined to centralized infrastructures, but span a continuum from cloud data centers to edge nodes and individual end devices. In this setting, optimally placing and orchestrating virtualized services becomes a critical and complex optimization problem. In this talk, I present a set of recent contributions addressing this class of problems, characterized by: (a) hard decisions on service placement and orchestration of modular applications, (b) scarce and heterogeneous resources, and (c) multi-layer network graphs. I highlight key challenges arising in this context, formulate the underlying combinatorial optimization problems, present solution approaches based on mixed integer programming and decomposition methods, and outline directions for future research.
LOCAL 07/05/2026 Connectivity in proof-nets: from classical to intuitionistic linear logic and the bang calculus, par Raffaele Di Donna
Raffaele Di Donna, IRIF  
Salle B107, bâtiment B, Université de Villetaneuse
07/05/2026    10:30 - 12:00
Résumé :
I will give you an overview of my recent work on linear logic proof-nets. The common thread is the study of the structural, geometric properties of proofs, and how they are related to the purely logical properties, with particular emphasis on the property of connectivity. I will present some interesting results from two related lines of research on classical and intuitionistic linear logic, and on the connection between proof-nets and the bang calculus. The starting point is a property that extends the Danos-Regnier correctness criterion for linear logic proof-structures. The property states that every correctness graph of the proof-structure is acyclic, and the number of its connected components is exactly one more than the number of nodes bottom or weakening. This is known to be necessary but not sufficient in MELL (multiplicative exponential linear logic) to recover a sequent calculus proof from a proof-structure. I will present fragments of linear logic for which this property is indeed a correctness criterion. In a suitable fragment of multiplicative linear logic with units, the criterion yields a characterization of the equivalence induced by permutations of rules in sequent calculus. In intuitionistic linear logic, the property is equivalent to the familiar requirement of having exactly one output conclusion, and it is sufficient for sequentialization in the axiom-free setting and in the fragment of MELL corresponding to the half-polarized typing system for call-by-push-value by Ehrhard. This fragment of MELL contains the translation of the bang calculus, a generalization of both call-by-name and call-by-value lambda-calculus, and, in particular, the image of the two Girard's translations. I will then explain more in detail the connection between the bang calculus and linear logic proof-nets: cut elimination simulates bang calculus reduction, and Girard's call-by-name and call-by-value translations of the lambda-calculus into proof-nets factor as the composition of the call-by-name and call-by-value translations of the lambda-calculus into the bang calculus with the translation of the bang calculus into proof nets. Finally, I give a geometric characterization of those proof-nets that arise from terms of the bang calculus.
CALIN 21/04/2026 L'algorithme de Bowyer-Watson, du plan euclidien aux surfaces hyperboliques, par Dorian Perrot
Dorian Perrot, Loria, Nancy  
Salle B107, bâtiment B, Université de Villetaneuse
21/04/2026    14:00 - 16:00
Résumé :
Une triangulation d'un ensemble de points dans le plan euclidien est dite de Delaunay si chaque cercle circonscrit à un triangle ne contient aucun autre sommet de la triangulation. Son extension à des surfaces, ainsi que certains algorithmes permettant de la calculer, se heurte à des difficultés topologiques (genre de la surface) et géométriques (systole de la surface). Cet exposé introduira la notion de triangulation de Delaunay, et présentera des méthodes de calcul permettant de la calculer comme l'algorithme de flip ou de Bowyer-Watson. Nous nous focaliserons ensuite sur ce-dernier, en l'étendant d'abord au tore, puis aux surfaces hyperboliques, en passant par la surface de Bolza. Aucun prérequis en géométrie hyperbolique, topologie ou algorithmique n'est nécessaire pour suivre l'exposé. Title : Bowyer-Watson algorithm, from the euclidean plane to hyperbolic surfaces. A triangulation of a set of points in the Euclidean plane is called a Delaunay triangulation if the circumcircle of each triangle does not contain any other vertex of the triangulation. Its extension to surfaces, as well as certain algorithms for computing it, encounters topological difficulties (genus of the surface) and geometric difficulties (systole of the surface). This talk will introduce the concept of Delaunay triangulation and present key computational methods, including the flip algorithm and Bowyer-Watson algorithm. We will then focus specifically on the Bowyer-Watson algorithm, extending it first to the torus, then to hyperbolic surfaces, with particular attention to the Bolza surface. The presentation requires no prior knowledge of hyperbolic geometry, topology, or algorithmics.
AOC 16/04/2026 Approximation Schemes for Planar Graph Connectivity Problems, par Meike Neuwohner
Meike Neuwohner  
Salle B107, bâtiment B, Université de Villetaneuse
16/04/2026    10:30 - 12:00
Résumé :
The k-Edge-Connected Subgraph problem and the k-Connectivity Augmentation problem are among the most basic Network Design problems and, consequently, have been heavily studied. Due to their approximation hardness, the gold standard in terms of approximation guarantee are strong constant factors. Interestingly, this approximation hardness does not carry over to planar graphs. In particular, the 2-Edge-Connected Subgraph problem admits a PTAS on planar graphs. However, the used techniques are very different from the celebrated BakerÂ’s framework, which is a standard way to design PTASs for planar graphs. The main obstacle of using BakerÂ’s technique in its classical form is that it requires a certain locality of the problem. However, k-edge/vertex-connectivity are global properties. We present a novel, and arguably clean, way to extend BakerÂ’s framework to deal with larger connectivity requirements. Based on this, we obtain a PTAS for the k-Edge-Connected Subgraph problem and its vertex analog, even with costs, as long as the max-to-min cost ratio is bounded by a constant. Moreover, together with further insights, we obtain a PTAS for the k-Connectivity Augmentation problem in the same cost setting. We complement this with an NP-hardness result for planar augmentation, showing that all our results are essentially tight. This is joint work with Vera Traub and Rico Zenklusen.
CALIN 14/04/2026 Asymptotique bivariée et récurrences linéaires, par Simon Barazer
Simon Barazer, IMB, Bordeaux  
Salle B107, bâtiment B, Université de Villetaneuse
14/04/2026    14:00 - 16:00
Résumé :
Dans cet exposé, je parlerai des méthodes récentes développées par A. Elveis-Price, W. Fang, B. Louf et M. Walner pour déterminer les comportements asymptotiques des solutions de récurrences bivariées. Ces méthodes se basent sur une approche d'abord heuristique qui permet de déterminer la forme de l'asymptotique, puis dans un second temps on utilise des arguments issus des marches aléatoires dans le quart de plan pour obtenir des équivalents. On verra comment ces méthodes peuvent s'appliquer au cas des nombres de Hurwitz monotones, que l'on a étudié avec B. Louf et si le temps le permet, aux généralisations possibles.
RCLN 13/04/2026 Towards Efficient and Effective Vocabulary in Sparse Information Retrieval, par Yuxuan ZONG
Yuxuan ZONG, ISIR  
Salle B107, bâtiment B, Université de Villetaneuse
13/04/2026    12:15 - 13:15
Résumé :
In the era of big data, information retrieval (IR) plays a central role in how information is accessed and consumed. Recent advances in Transformer-based neural models have substantially improved retrieval performance. Two major paradigms have emerged in this context: learned sparse retrieval, which represents texts using weighted vocabulary terms, and generative retrieval, which formulates retrieval as the generation of a document identifier. While both approaches have shown strong performance, they also exhibit important limitations. Sparse retrieval methods are often constrained by the fixed vocabulary of the underlying language model, limiting their adaptability, whereas generative retrieval methods rely on arbitrary document identifiers that tend to generalize poorly to unseen documents. In this thesis, we explore how these two paradigms can be combined to obtain more efficient and more effective retrieval representations. Our core idea is to construct sparse retrieval vocabularies from learning rather than from predefined lexical tokens. We first propose REFERENTIAL and HotBERT to investigate the use of hierarchical structured identifiers as the vocabulary representation for retrieval, whose coarse-to-fine representation is designed to capture global semantics at higher levels and progressively refine finer-grained distinctions. While this representation proves expressive and effective, our analysis reveals that directly learning and optimizing hierarchical identifiers is challenging in practice. Motivated by this observation, we introduce SAE-SPLADE, a sparse retrieval framework built on sparse autoencoders (SAE), which is an architecture that learn sparse, interpretable latent representations. By using SAE latents as the retrieval vocabulary, SAE-SPLADE removes the dependence on fixed token vocabularies and improves flexibility and representation capacity. Finally, recognizing the efficiency challenges HotBERT, we propose a theoretically lossless token-pruning method for late interaction models that reduces computation while preserving retrieval performance.
LOCAL 09/04/2026 From itrees to mtrees: monadic interpreters in Rocq as models of first order programming languages, par Yannick Zakowski
Yannick Zakowski, Inria  
Salle B107, bâtiment B, Université de Villetaneuse
09/04/2026    10:30 - 12:00
Résumé :
Over the last few years, we have been experimenting with using flavours of (coinductive) monadic interpreters to represent computations in Rocq. The basic toolbox of the approach has been embedded back in 2020 in the Interaction Trees library, and notably used at scale in the Vellvm project to give a formal semantics to LLVM IR. In this talk, I will walk through this experience, with the aim to focus in particular on the comparatively more recent treatment of non-determinism. I will introduce so-called Choice Trees, a second library adding support for a choice operator. On top of this primitive operation, we implement shallow combinators for various flavours of parallel composition, whether w.r.t. to shared memory model or communication-based computations. Furthermore, additionally to the monadic interpretation of operations, choice trees support refinements of its internal branching, allowing for executing the semantics against specific schedulers, whether internally to Rocq or on the OCaml side. Finally, and if time permit, I will move the focus to ongoing work with Peio Borthelle around, for lack of talent in naming, monadic trees. This time, we step back to a mathematically more natural approach, albeit more challenging to implement: rather than implementing effect through monad transformers on top of itrees, we directly construct the final coalgebra of the composition of a monad `m` with a functor of observation. ITrees become the specialised case where "m=id", CTrees are essentially isomorphic to the case of "m=fam", the functor of families, and a more generic theory can be established.
CALIN 07/04/2026 Cubical realizations of framing lattices, par Clément Chenevière
Clément Chenevière, LIGM, Université Gustave Eiffel  
Salle B107, bâtiment B, Université de Villetaneuse
07/04/2026    14:00 - 16:00
Résumé :
Framing lattices were introduced very recently in [von Bell--Ceballos, 2025] and [Berggren--Serhiyenko, 2024] as a wide family of lattices containing many generalizations of the Tamari lattice and the weak order. They are associated to a directed acyclic graph, together with a framing, a choice of total orders on incoming and outgoing edges at each vertex. Such a choice of framing enables to decide whether two routes (maximal paths) are crossing. Framing lattices were then defined as an order on maximal collections of non crossing routes. In an ongoing work with Jonah Berggren, we introduce cornered cliques as a new combinatorial model for the elements of a framing lattice, with explicit bijections with maximal cliques. These enable us to provide cubical coordinates for all framing lattices, for which covering relations change only one coordinate, and comparison in the lattice corresponds to componentwise comparison. These specialize to the well-known bracket vectors for the Tamari lattice, and to an enhanced version of the Lehmer code for the weak order.
CALIN 31/03/2026 Low discrepancy sequences in combinatorics, par François Clément
François Clément, University of Washington  
Salle B107, bâtiment B, Université de Villetaneuse
31/03/2026    14:00 - 16:00
Résumé :
Low-discrepancy sequences are the best discrete approximations of the continuous uniform distribution. Two of the most classical constructions are the van der Corput sequence and the family of Kronecker sequences. Apart from their uniformity, their construction methods lead to very nice mathematical properties. In this talk, I will present some ways to use their regularity, first to tackle an old problem of Erdos and de Bruijn (1949) on lengths of consecutive segments, and then to obtain embeddings in translation surfaces.
LOCAL 26/03/2026 Bismulations dans les calculs linéaires, par Sergueï Lenglet
Sergueï Lenglet, LIPN, Equipe Molotov  
Salle B107, bâtiment B, Université de Villetaneuse
26/03/2026    10:30 - 12:00
Résumé :
La bisimulation est une technique de preuve pour montrer que 2 programmes "font la même chose". Je ferai un panorama rapide des bisimulations pour le lambda-calcul, avant de faire l'état de l'art des bisimulations définies jusqu'ici pour les calculs "linéaires" et voir quelles questions restent pour l'instant non résolues.
SAFER 25/03/2026 Approches formelles pour la modélisation, le contrôle, l’analyse de performances, la reconfiguration et la cybersécurité des systèmes à événements discrets, par Saïd Amari
Saïd Amari  
Salle B107, bâtiment B, Université de Villetaneuse
25/03/2026    14:30 - 16:00
Résumé :
Ce séminaire présente des travaux portant sur le développement d’approches formelles centralisées, modulaires et distribuées pour la modélisation, le contrôle, l’analyse des performances, la reconfiguration et la cybersécurité des systèmes à événements discrets. Ces travaux s’appuient sur différents formalismes tels que les réseaux de Petri (temporisés et colorés), les automates temporisés avec gardes, les automates hybrides, ainsi que les algèbres Max-Plus et Min-Plus et les séries formelles colorées. L’objectif est de proposer des méthodes d’analyse et d’aide à la décision permettant de garantir certaines propriétés des systèmes, notamment en termes de performance, de sûreté et de résilience. Une attention particulière est portée aux problématiques de modélisation et de vérification analytique dans des architectures d’automatisation distribuées (collaboration avec EDF). Les techniques formelles établies sont illustrées à travers plusieurs domaines d’application, notamment la résilience des chaînes logistiques, l’analyse du temps de réponse des systèmes de commande en réseau, les systèmes manufacturiers soumis à contraintes et la sécurité des systèmes cyber-physiques.
SAFER 25/03/2026 Parallel and Domain-Aware SAT Solving: Application to Blockchain Analysis, par Souheib Baarir
Souheib Baarir  
Salle B107, bâtiment B, Université de Villetaneuse
25/03/2026    13:00 - 14:00
Résumé :
This talk presents research contributions on Boolean Satisfiability (SAT) solving and its application to the analysis of discrete systems. The first part focuses on parallel SAT solving, addressing key issues such as modular solver design, the articulation between divide-and-conquer and portfolio approaches, and effective learned-clause sharing. In this context, the PaInleSS framework is introduced as a generic platform for building efficient parallel SAT solvers. The second part considers domain-aware SAT solving through programmatic extensions of CDCL, showing how problem-specific knowledge can improve solving strategies, especially in bounded model checking. The presentation concludes with an application to the verification of blockchain smart contracts, where SAT-based reasoning provides a promising basis for analyzing security- and safety-critical properties at scale.
SAFER 24/03/2026 Fiabilité et QoS dans le continuum : vers une ingénierie formelle bout-en-bout des services IoT-Fog-Cloud, par Mohamed Graiet
Mohamed Graiet  
Salle A303, bâtiment B, Université de Villetaneuse
24/03/2026    15:30 - 16:30
Résumé :
Les applications IoT déployées dans le continuum IoT–Fog–Cloud doivent concilier des contraintes de ressources, qualité de service (QoS), hétérogénéité et dynamique d’exécution, tout en restant robustes face aux pannes. Dans ce contexte, la fiabilité ne peut pas reposer uniquement sur des tests ad hoc : elle doit être construite et argumentée de manière systématique, depuis les exigences jusqu’au comportement observé en exécution. Nous présentons d’abord une approche centrée sur la vérification de mécanismes de tolérance aux pannes dans l’IoT multi-couches. La modélisation en Event-B, via raffinement et invariants, permet de formaliser des stratégies telles que la dégradation contrôlée, le basculement vers des composants de secours et la reprise/retour à un état sûr, tout en générant des obligations de preuve garantissant que ces mécanismes préservent les propriétés de sûreté attendues. Cette étape pose un socle : la résilience doit être spécifiée et justifiée rigoureusement, couche par couche, dans des architectures distribuées. Nous passons ensuite au Fog, où l’enjeu devient la composition de services sous contraintes, depuis les exigences jusqu’au déploiement (et, le cas échéant, l’interaction avec des services cloud). La démarche se décline en étapes : (i) capturer et structurer les exigences (fonctionnelles, coordination, ressources, QoS), (ii) décider un placement correct des composants, (iii) établir une configuration/reconfiguration d’un service composite en arbitrant entre efficacité QoS et fiabilité (notamment transactionnelle), puis (iv) vérifier formellement la cohérence de la composition et des interactions par Event-B. Dans cette dynamique, une perspective consiste à mobiliser des agents conversationnels (systèmes multi-agents conversationnels) pour soutenir l’orchestration et la reconfiguration (négociation de contraintes, adaptation, selection, assistance à la décision), tout en conservant un noyau formel vérifiable. Enfin, nous motivons une évolution méthodologique : Event-B est très puissant pour prouver des invariants et structurer la correction, mais il n’est pas toujours le plus adapté pour explorer exhaustivement certains comportements dynamiques typiques des systèmes distribués (interleavings concurrents, scénarios d’exécution, blocages, vivacité, effets de reconfiguration). Pour couvrir ces aspects, nous proposons de compléter la preuve par du model checking, en introduisant une transformation Event-B ? Réseaux de Petri Colorés (CPN). Cette transformation vise à obtenir un modèle exécutable et analysable, permettant ensuite d’appliquer des techniques de vérification automatique (exploration d’espace d’états, détection de deadlocks, propriétés de vivacité/atteignabilité) et de refermer la boucle : les contre-exemples et scénarios trouvés alimentent l’amélioration du modèle Event-B, des exigences et des politiques de configuration. Mots-clés Continuum IoT–Fog–Cloud, Fiabilité / Résilience, Qualité de service (QoS), Tolérance aux pannes multi-couches, Composition et (re)configuration de services, Placement sous contraintes, Vérification formelle, Event-B, Réseaux de Petri colorés (CPN), Model checking, systèmes multi-agents conversationnels
SAFER 24/03/2026 Rational Synthesis in Resource-Constrained Multi-Agent Systems, par Youssouf Oualhadj
Youssouf Oualhadj  
Salle A303, bâtiment A, Université de Villetaneuse
24/03/2026    14:00 - 15:00
Résumé :
Rational synthesis studies the automatic construction of controllers that interact with rational agents pursuing their own objectives. Rather than assuming a hostile environment, this framework accounts for strategic behavior and equilibrium reasoning in multi-agent systems. In this talk, we consider rational synthesis in the presence of shared resources. Agents interact in turn-based games where actions may consume or replenish common resources, and must satisfy qualitative temporal objectives while avoiding resource depletion. We discuss how resource constraints fundamentally impact the synthesis problem, how the model evolves from single to multiple resources, and what this reveals about the limits of automated controller design.
CALIN 24/03/2026 Réalisations polyédrales de tores plats, par Florent Tallerie
Florent Tallerie  
Salle B107, bâtiment B, Université de Villetaneuse
24/03/2026    14:00 - 16:00
Résumé :
On peut facilement plier une feuille de papier rectangulaire, afin de réaliser un cylindre droit : il suffit de plier la feuille en trois de manière à obtenir un prisme à section triangulaire. Mais qu'en est-il si l'on veut recoller les bords triangulaires de ce prisme pour réaliser un tore plat ? Nous verrons dans cet exposé que cela est toujours possible, ce quel que soit les polygones papiers de départ considérés, et les instructions de recollement choisis. Nous étudierons également la question suivante : est-il possible de réaliser tous les tores plats avec une combinatoire fixée ? Enfin, si le temps le permet, nous évoquerons la généralisation de ces questions à des surfaces polyédrales de genre 2, dites de translation.
SAFER 23/03/2026 Security Analysis and Resilient Supervisory Control of Cyber-Physical Systems, par Gaiyun Liu
Gaiyun Liu  
Salle A303, bâtiment A, Université de Villetaneuse
23/03/2026    13:00 - 14:00
Résumé :
This talk is organized into three main parts. The first part introduces research on Petri net structure theory and robust/adaptive supervisory control of discrete event systems, including controllability of siphons, supervisory control based on time constraints, and robust/adaptive supervisory control for systems with uncertainties caused by unreliable resources or operations. The second part concerns security analysis and resilient control of cyber-physical systems (CPSs) under information impairment. It discusses opacity analysis and resilient supervisory control strategies in the presence of cyberattacks and malicious intrusions. Furthermore, the talk addresses fault diagnosis in CPSs with communication delays. Finally, the talk highlights several future research directions, including prognosability analysis in CPSs with communication delays and the integration of data-driven approaches with supervisory control theory, aiming to enhance the security and resilience of next-generation CPSs.
AOC 20/03/2026 Warm-Starting QAOA for Combinatorial Optimization via Difference-of-Convex Optimization - A Case Study on Max-Cut, par Viet Hung Nguyen
Viet Hung Nguyen  
Salle G202, Université de Villetaneuse
20/03/2026    14:00 - 16:00
Résumé :
The Quantum Approximate Optimization Algorithm (QAOA) has recently been proposed as a heuristic framework for solving combinatorial optimization problems through a hybrid classical–quantum optimization procedure. The algorithm alternates parameterized quantum transformations with a classical optimization step that adjusts the circuit parameters in order to increase the probability of sampling high-quality solutions. A key factor influencing the performance of QAOA is the choice of the initial state. In standard implementations, the algorithm starts from a uniform superposition over all candidate solutions, which does not exploit structural information about the original optimization problem and may lead to inefficient parameter optimization and lower-quality solutions. In this talk, we propose a warm-start strategy based on continuous optimization, using the Difference-of-Convex Algorithm (DCA). The idea is to exploit a continuous relaxation of the original optimization problem in order to construct an informed initialization that biases the search toward promising regions of the solution space. We illustrate the approach on instances of the Max-Cut problem and show that this strategy can significantly improve the approximation ratios obtained by QAOA. This is a joint work with HA Huy Phuc Nguyen et TA Anh Son.
AOC 19/03/2026 Positive spanning sets and their connections to polyhedra, par Clément Royer
Clément Royer  
Salle G205, Université de Villetaneuse
19/03/2026    10:30 - 12:00
Résumé :
Positive spanning sets (PSSs), that span a given space through nonnegative linear combinations, have been successfully employed to design and analyze derivative-free optimization algorithms. Although linear algebra is a natural framework for studying PSSs, polyhedral geometry can provide additional insights on the structure of PSSs. In this talk, I will first introduce the concept of positive spanning sets, together with its use in derivative-free optimization. I will then focus on the specific case of polyhedral constrained problems, and explain how to generate positive spanning sets that conform to the geometry of those constraints. Finally, I will turn to a perhaps unexpected construction of PSSs of smallest cardinality through polytopes, and discuss several associated open questions. This talk is based on joint works with Denis Cornaz, Sébastien Kerleau and Lindon Roberts.
CALIN 24/02/2026 Construisons le cône sous-modulaire par récurrence, par Germain Poullot
Germain Poullot, Osnabrück University  
Salle B107, bâtiment B, Université de Villetaneuse
24/02/2026    14:00 - 16:00
Résumé :
Cette présentation plonge, en particulier, dans l'article https://arxiv.org/abs/2510.03177 avec Georg Loho et Arnau Padrol. Nous commencerons par une (longue) introduction aux déformations de polytopes. Un permutoèdre déformé (aussi appelé permutoèdre généralisé, ou fonction sous-modulaire) est un polytope dont toutes les arêtes ont pour direction $e_i - e_j$ pour certains $i \neq j$. L'ensemble des permutoèdres déformés vivant dans $\mathbb R^n$ forme un cône, le cône sous-modulaire. Nous proposons une construction "inductive" du cône sous-modulaire, en utilisant une opération nommée GP-sum : à partir de deux permutoèdres déformés dans $\mathbb R^n$, nous créons (bijectivement) un permutoèdre déformé dans $\mathbb R^{n+1}$. Munis de cette construction, nous créons de nouveaux rayons du cône sous-modulaire, c'est-à-dire de nouveaux permutoèdres déformés indécomposables (au sens de la somme de Minkowski). Cela nous permet d'améliorer les bornes connues sur le nombre de rayons du cône sous-modulaire, notamment en produisant $2^{2^n}$ rayons. Plus encore, nous étudions le f-vecteur du cône sous-modulaire, son nombre total de faces, et le nombre de ses faces simplicial, grâce à la nouvelle partition que cette construction inductive nous donne.
CALIN 17/02/2026 Trier des tableaux partiellement pré-triés, par Vincent Jugé
Vincent Jugé, LIGM, Université Gustave Eiffel  
Salle B107, bâtiment B, Université de Villetaneuse
17/02/2026    14:00 - 16:00
Résumé :
Même si trier une permutation aléatoire requiert n log(n) comparaisons en moyenne, il existe de nombreux cas d'usage où les tableaux que l'on souhaite trier ne sont pas des permutations aléatoires : soit ils contiennent de longues plages contiguës déjà triées, soit ils contiennent peu de valeurs distinctes. L'algorithme TimSort, utilisé en Java pour trier des tableaux d'objets composites, a été conçu spécifiquement pour être plus efficace sur de tels tableaux pré-triés. Nous découvrirons comment cet algorithme et ses variantes fonctionnent et pourquoi ils sont efficaces.
LOCAL 17/02/2026 Lambda-calculus and space complexity, par Thibaut Balabonski
Thibaut Balabonski, LMF, Paris Saclay  
Salle B107, bâtiment B, Université de Villetaneuse
17/02/2026    12:30 - 13:30
Résumé :
While the ?-calculus is widely recognized as a model of computation, equivalent to Turing and other machines, its relevance for the study of complexity has long been unclear. Its central operation, ?-reduction, seems at first sight too rich and complex to be considered as an appropriate atomic unit of computation. We learned only quite recently that the natural complexity measures (number of ?-reductions for time, size of terms for space) were indeed ''reasonable'' measures, defining the same complexity classes (P, NP, PSPACE, ...) as the Turing standard. In this talk I will propose a refined —but still simple and natural— definition of space complexity for the ?-calculus, sensitive to sub-linear space. In particular, this measure allows a ?-calculus-based characterization of algorithms running in logarithmic space (class L), thus extending the range of complexity classes for which the ?-calculus is an appropriate vessel.
AOC 12/02/2026 Properties of matroids in picking games against Greedy, par Emiliano Lancini
Emiliano Lancini  
Salle A303, bâtiment A, Université de Villetaneuse
12/02/2026    10:30 - 12:00
Résumé :
Given an hypergraph on a set of n ordered vertices, we define an independent set X to be feasible, if X is a possible outcome for a player in a sequential picking game, against a greedy adversary, where no hyperedge can be contained in the union of both outcomes. We prove that testing feasibility is NP-complete, even if the hypergraph is a graph, but it becomes polynomial (in n) for matroid hypergraphs, that is, when the hyperedges are the circuits of some matroid (in which independence can be tested with an oracle). We prove also that optimizing a linear function over feasible sets is NP-hard for graphs and matroid hypergraphs, even for graphic matroids, but it becomes polynomial for laminar matroids.
LOCAL 12/02/2026 Toposes with enough points as categories of étale spaces, par Umberto Tarantino
Umberto Tarantino, IRIF  
Salle B107, bâtiment B, Université de Villetaneuse
12/02/2026    10:30 - 12:00
Résumé :
As originally showed by Barr, a topology on a set X can be equivalently described as a 'convergence relation' between elements of X and ultrafilters on X: in other words, a spatial locale can be recovered from its set of points once it is endowed with appropriate extra structure defined in terms of ultrafilters. In this talk, I will present a similar reconstruction result for (Grothendieck) toposes with enough points, a categorification of spatial locales: every such topos can be recovered up to equivalence from its category of points, provided that the latter is endowed with appropriate extra structure involving ultrafilters. In logical terms, this reads as a (strong) conceptual completeness theorem for geometric logic. Towards this goal, I will introduce ultraconvergence spaces, a profunctorial generalization of Makkai's ultracategories inspired by Barr's convergence relations. This talk is based on joint work with Quentin Aristote, Sam van Gool and Jérémie Marquès.
CALIN 10/02/2026 Hitting affine families of polyhedra, with applications to robust optimization, par Sarah Wajsbrot
Sarah Wajsbrot, Loria, Nancy  
Salle B107, bâtiment B, Université de Villetaneuse
10/02/2026    14:00 - 16:00
Résumé :
Geometric hitting set problems, in which we seek a smallest set of points that collectively hit a given set of ranges, are ubiquitous in computational geometry. Most often, the set is discrete and is given explicitly. We propose new variants of these problems, dealing with continuous families of convex polyhedra, and show that they capture decision versions of the two-level finite adaptability problem in robust optimization. We show that these problems can be solved in strongly polynomial time when the size of the hitting/covering set and the dimension of the polyhedra and the parameter space are constant. We also show that the hitting set problem can be solved in strongly quadratic time for one-parameter families of convex polyhedra in constant dimension. This leads to new tractability results for finite adaptability that are the first ones with so-called left-hand-side uncertainty, where the underlying problem is non-linear. Joint work with Jean Cardinal and Xavier Goaoc. Manuscript: https://arxiv.org/abs/2504.16642
AOC 05/02/2026 Betweenness Centrality and Counting Problems, par Mehdi Naima
Mehdi Naima  
Salle B107, bâtiment B, Université de Villetaneuse
05/02/2026    10:30 - 12:00
Résumé :
Betweenness centrality (BC), introduced in 1977, is a fundamental measure of node importance in networks, widely used in fields ranging from sociology to computer science. BC quantifies the extent to which a node lies on shortest paths between pairs of nodes, making its computation closely tied to the enumeration of these paths. In this work, we investigate the computational complexity of determining BC for all nodes in a graph, highlighting the challenges associated with exhaustive shortest-path counting. We further examine extensions of BC to dynamic graphs, where edges carry temporal information and optimal paths are determined not only by topology but also by timing constraints (i.e., fastest paths). We explore the hardness of computing BC under such dynamic conditions and discuss how temporal dependencies complicate classical shortest-path approaches. Our study aims to unify understanding of BC computation across static and temporal graph models and to identify open problems in efficiently counting relevant paths in these settings.
AOC 29/01/2026 On Multidimensional Disjunctive Inequalities for Chance-Constrained Stochastic Problems with Finite Support, par Marius Roland
Marius Roland  
Salle B107, bâtiment B, Université de Villetaneuse
29/01/2026    10:30 - 12:00
Document attaché
Résumé :
This presentation addresses linear Chance-Constrained Stochastic Problems (CCSPs) with finite support. We begin by motivating the study of CCSPs through illustrative examples and providing intuition regarding the concept of feasibility in this context. Subsequently, we discuss the computational challenges inherent to these problems, specifically the nonconvex structure of the feasible region and the limitations of the standard big-M reformulation. These challenges necessitate the use of branch-and-cut approaches. To this end, we review existing families of valid inequalities, such as quantile inequalities and mixing inequalities. This background sets the stage for the primary contribution of this work: a new class of valid inequalities termed multi-disjunctive inequalities. We construct these inequalities by exploiting a disjunctive property inherent to the mathematical formulation of CCSPs. Theoretical analysis reveals that the closure of these multi-disjunctive inequalities constitutes a proper subset of the closure generated by previously proposed families. We perform numerical experiments within a pure cutting-plane framework to compare the closures obtained by enumerating all violated valid inequalities. The results demonstrate that multi-disjunctive inequalities significantly strengthen the continuous relaxation of the considered CCSPs compared to existing quantile and mixing-set inequalities. Furthermore, we evaluate the performance of these inequalities embedded within a branch-and-cut framework. Our results indicate that the proposed approach significantly outperforms existing methods on both standard literature instances and newly generated instances designed to be computationally challenging.
CALIN 27/01/2026 Les arbres biaisés par la hauteur: quelques nouveaux résultats, par Meltem Ünel
Meltem Ãœnel, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/01/2026    14:00 - 16:00
Résumé :
Étant donné $n \in \mathbb{N}$ et $\mu \in \mathbb{R}$, un arbre de taille $n$ biaisé par la hauteur est un arbre planaire aléatoire $T_n$ à $n$ sommets dont la loi est donnée par $P(T_n = t ) \propto e^{-\mu h(t)}$, où $t$ est un arbre fixe à $n$ sommets, et $h(t)$ est la hauteur de $t$ . Dans cet exposé on va présenter quelques statistiques de ces arbres quand $\mu=\mu(n)$ est une suite à termes positifs dépendant de $n$: la limite d'échelle quand $\mu(n) \sim 1/ \sqrt{n}$, la hauteur ainsi que le comportement autour de la racine quand $0 \leq \mu(n) \ll n$. L'exposé est basé sur arXiv:2512.17747 en commun avec L. Addario-Berry, B. Corsini et N. Maitra.
LOCAL 22/01/2026 Adapters: a type-theoretic foundation for type casting, par Meven Lennon-Bertrand
Meven Lennon-Bertrand, IRIF  
Salle B107, bâtiment B, Université de Villetaneuse
22/01/2026    10:30 - 12:00
Résumé :
A fundamental operation in type systems is the ability to *type cast*, that is, take a value of a given type and use it at different type, assuming some information relating the source and target. This manifests under many names: subtyping, coercion, transport... These various mechanisms are particularly essential in dependent type theory, where types are extremely rich and precise. Yet they have a complicated history, and are rather poorly understood from a theoretical standpoint. In my talk I will explain the challenges faced with cast systems, and how we can understand and fix some of them with the type theorist's glasses on. The focus will be particularly on *structural* casts, those that follow the structure of type formers, which led us to a surprisingly deep and beautiful type theoretic quest, revolving around the idea that structural casts arise from the fact that all type formers are really functors.
CALIN 20/01/2026 Lattice walks with large steps in the first quadrant : algebraicity of the stretched Gessel models, par Pierre Bonnet
Pierre Bonnet, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
20/01/2026    14:00 - 17:00
Résumé :
Lattice walks confined in the first quadrant have been subject to an extended study for about a decade, showing a great variety of techniques to handle functional equations with catalytic variables. A work of Pierre Bonnet and Charlotte Hardouin of 2024 extended those tools in the context of the study of walks based upon models with arbitrarily large steps, allowing to effectively conduct a strategy devised by Bousquet-Mélou, Olivier Bernardi and Kilian Raschel of 2016, providing the algebraicity proofs of some models. In this talk, I show how these tools show the algebraicity of an infinite family of models of walks derived from the Gessel models.
LOCAL 08/01/2026 Abstraction Functions as Types: Modular Verification of Behavior and Cost, par Harrison Grodin
Harrison Grodin, Carnegie Mellon University  
Salle B107, bâtiment B, Université de Villetaneuse
08/01/2026    10:30 - 12:00
Résumé :
Software development depends on the use of libraries whose public specifications inform client code and impose obligations on private implementations; it follows that verification at scale must also be modular, preserving such abstraction. Hoare's influential methodology uses abstraction functions to demonstrate the coherence between such concrete implementations and their abstract specifications. However, the Hoare methodology relies on a conventional separation between implementation and specification, providing no linguistic support for ensuring that this convention is obeyed. The presented work proposes a synthetic account of Hoare's methodology within univalent dependent type theory by encoding the data of abstraction functions within types themselves. This is achieved via a phase distinction, which gives rise to a gluing construction that renders an abstraction function as a type and a pair of modalities that fracture a type into its concrete and abstract parts. A noninterference theorem governing the phase distinction characterizes the modularity guarantees provided by the theory. This approach scales to verification of cost, allowing the analysis of client cost relative to a cost-aware specification. A monadic sealing effect facilitates modularity of cost, permitting an implementation to be upper-bounded by its specification in cases where private details influence observable cost. The resulting theory supports modular development of programs and proofs in a manner that hides private details of no concern to clients while permitting precise specifications of both the cost and behavior of programs.
CALIN 16/12/2025 On the enumeration of records of rooted trees and rooted forests, par Mercedes Rosas
Mercedes Rosas, Universidad de Sevilla  
Salle B107, bâtiment B, Université de Villetaneuse
16/12/2025    14:00 - 17:00
Résumé :
A record of a rooted Cayley tree is a node whose label is the largest along the unique path to the root. In this work, we find elegant functional equations relating the generating functions for records of rooted Cayley trees and for records of forests of rooted trees with the Cayley tree function, and explore the consequences of our results. This is join work with Adrián Lillo and Stefan Trandafir.
CALIN 09/12/2025 Spanning trees in the assignment problem: two theorems and a conjecture, par Andrea Sportiello
Andrea Sportiello , LIPN, CNRS  
Salle B107, bâtiment B, Université de Villetaneuse
09/12/2025    14:00 - 17:00
Résumé :
The "Minimum Matching Problem" consists in finding an independent edge set of minimum weight M*(G) in a given edge-weighted undirected graph G. If G is bipartite, we deal with the "Assignment Problem". We consider a version of the problem in which we take the union of the optimal matchings for various slightly-modified versions of the base graph: H_J(G)=Union_{U in J} M*(G_U). In this talk we will provide two families of theorems: (1) we prove that, in two distinct settings for the Assignment Problem, the graphs H_J, as well as certain associated graphs H'_J, are in fact spanning trees on the pertinent base graphs G and G'; (2) in the two settings above, if the weights of the graph edges are given by the p-th power of the Euclidean distance for points configurations on the plane, the tree H_J is non-crossing (that is, its natural embedding in the plane has no crossing edges) when p=1, and (more surprisingly) the associated tree H'_J is non-crossing when p=2. Our main motivation for investigating theorems of this form comes from (a family of) conjectures in Statistical Mechanics, that we will illustrate in future work: in the Random Euclidean Assignment Problem (i.e., when the points are chosen i.i.d. on a domain of the plane), for p=2, the two settings above give trees H'_J which are asymptotically distributed as the Uniform Spanning Tree with free and wired boundary conditions, in the two cases. In particular, suitable paths on the tree in the second setting are asymptotically distributed as a SLE at kappa=2. Work in collaboration with Sergio Caracciolo and Gabriele Sicuro
SAFER 08/12/2025 Titre bientôt disponibleProbabilistic verification of strategic ability in multi-agent systems with continuous time, par Teofil Sidoruk
Teofil Sidoruk  
Salle A303, bâtiment B, Université de Villetaneuse
08/12/2025    12:45 - 14:00
Résumé :
The recently proposed logics PTATL and PSTCTL extend ATL and SCTL, respectively, to include both continuous time and stochastic aspects (probabilistic transition relations in models and agents' choices in strategies). As such, they have significant expressive power, but also high model checking complexity. I will present the essential theoretical background, as well as our approach to practical verification of these logics in asynchronous multi-agent systems, which combines two state-of-the-art tools IMITATOR and PRISM.
SAFER 08/12/2025 Consensus in Models for Opinions Dynamics with Generalized-Bias, par Juan Fernando Paz
Juan Fernando Paz  
Salle A303, bâtiment A, Université de Villetaneuse
08/12/2025    11:50 - 12:50
Résumé :
Interest is growing in social learning models where users share opinions and adjust their beliefs in response to others. Our work introduces generalized-bias opinion models, an extension of the DeGroot model, that capture a broader range of cognitive biases. These models can encompass, among others, dynamic (changing) influences, as well as in-group favoritism and out-group hostility, a bias where agents may react differently to opinions from members of their own group compared to those from outside. The reactions are formalized as arbitrary functions that depend, not only on opinion difference, but also on the particular opinions of the individuals interacting. Under certain reasonable conditions, all agents –despite their biases– will converge to a consensus if the influence graph is strongly connected, as in the original DeGroot model.
LOCAL 04/12/2025 A compositional approach to Taylor expansion, par Aymeric Walch
Aymeric Walch, ISAE SUPAERO  
Salle B107, bâtiment B, Université de Villetaneuse
04/12/2025    10:30 - 12:00
Résumé :
The combination of the theory of differential calculus with the theory of programming languages is an active field of research, with the development of automated differentiation and of the differential lambda calculus. It is well known that differentiation can be turned into a compositional operation, using the tangent bundle construction, also called dual numbers in automated differentiation. In this talk, we explain how Taylor expansion at any degree is also captured by a compositional operation. This operation is similar to jet bundles found in differential geometry, and to higher order dual numbers that have found recent applications in automated differentiation. We will then discuss how category theory is a nice framework to describe those ideas. Formally, Taylor expansion is captured as a functor, and the axioms of differential calculus boil down to naturality equations that turn this functor into a monad. We will then briefly explain how those ideas can be applied to the study Taylor expansion in quantitative semantics of Linear Logic.
CALIN 02/12/2025 Equiprojective polytopes in high dimension, par Alice Cousaert
Alice Cousaert, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
02/12/2025    14:00 - 17:00
Résumé :
A 3-dimensional polytope (the convex hull of finitely many points) is said to be k-equiprojective if almost every planar projections is a k-gon where k is a fixed integer. Two characterisations were established respectively in 2008 by Masud Hasan and Anna Lubiw and in 2024 by Théophile Buffière and Lionel Pournin in the 3-dimensional case. I will present you a way to generalise the definition of equiprojectivity to d-dimensional polytopes, as well as the tools I built in order to generalise the two different characterisations.
LOCAL 27/11/2025 Towards Formal Semantics and Reasoning for OCaml, par Rémy Seassau
Rémy Seassau, INRIA Paris  
Salle B107, bâtiment B, Université de Villetaneuse
27/11/2025    10:30 - 11:30
Résumé :
OCaml is a multi-paradigm, high-level programming language with years of development and a modern set of features such as concurrency and effect handlers. The Osiris project is an attempt to equip a nontrivial fragment of OCaml with a formal semantics and with an interactive program verification environment, hosted inside the Rocq proof assistant. In this talk, I will present OLang, a nontrivial fragment of OCaml, which includes first-class functions, ordinary and extensible algebraic data types, pattern matching, references, exceptions, and effect handlers. I will show how we define the dynamic semantics of a realistic language as a monadic interpreter running atop a custom monad where computations are internally represented as trees of operations and effects are interpreted with a small-step semantics. I will present two program logics for OLang: a stateless Hoare Logic allows reasoning about so-called pure programs, and an Iris-based Separation Logic allows reasoning about arbitrary programs.
CALIN 25/11/2025 La géométrie des codes linéaires et des applications récentes, par Martino Borello
Martino Borello, LAGA  
Salle B407, bâtiment B, Université de Villetaneuse
25/11/2025    14:00 - 16:00
Résumé :
Il est bien connu qu’un code linéaire non dégénéré de longueur n et de dimension k peut être associé à un ensemble de n points (avec multiplicités) dans un espace projectif de dimension k?1. Certaines propriétés des codes peuvent être interprétées géométriquement. Cette perspective relie les codes MDS aux problèmes impliquant des arcs dans les espaces projectifs (la fameuse conjecture MDS a été initialement formulée comme un problème de géométrie projective par Segre), les problèmes de recouvrement aux ensembles saturants, les codes minimaux aux ensembles bloquants forts, etc. Dans cette présentation, nous illustrerons certains résultats récents obtenus en utilisant cette approche géométrique pour les codes en métrique de Hamming et nous esquisserons à la fin comment cela peut être généralisé à d’autres métriques, telles que les métriques rang et somme-rang.
AOC 20/11/2025 Frank-Wolfe methods for convex quadratic optimization, par Mathieu Besançon
Mathieu Besançon  
Salle B107, bâtiment B, Université de Villetaneuse
20/11/2025    10:30 - 12:00
Résumé :
I will go over some recent results on Frank-Wolfe methods, presenting the core aspects of the algorithms and highlight properties of the algorithms that make them relevant for convex quadratic optimization, despite the first-order access to the objective. In particular, we will go over the active set identification property some Frank-Wolfe variants enjoy and a use of linear system or linear optimization solvers to accelerate convergence and reach finite-time guarantees. I will then present one application to sparse flow decomposition for RNA-seq data analysis.
AOC 18/11/2025 Partitioning a Graph into Connected Components, par Hande Yaman
Hande Yaman  
Salle G201
18/11/2025    14:00 - 16:00
Résumé :
In this talk, we study problems that involve partitioning the vertices of an undirected graph into a given number of pairwise disjoint sets such that each set induces a connected subgraph. We first propose valid inequalities, which extend and generalize the ones in the literature, and report on computational experiments demonstrating their use (joint work with P. Moura and R. Leus). Then, we extend this problem to also compute a spanning tree for each set of the partition such that the weight of the heaviest tree is minimized. We investigate the complexity of this problem and present formulations and solution methods, which we compare with an experimental study (joint work with M. Davari and P. Moura). Finally, we consider a practical problem encountered in power system restoration, which involves partitioning a power network into connected subnetworks, one for each black start generator, such that the restoration time is minimized. We propose a solution method that uses a new formulation and properties of optimal solutions and report computational results (joint work with H. Çal?k and D. Van Hertem).
CALIN 18/11/2025 Algebraic shifting and area rigidity of surfaces, par Denys Bulavka
Denys Bulavka  
Salle B107, bâtiment B, Université de Villetaneuse
18/11/2025    14:00 - 17:00
Résumé :
Algebraic shifting, introduced by Kalai in the 80's, is an operator that canonically associates a shifted complex to a given simplicial complex. The advantage of this operator is that it preserves many combinatorial, topological and algebraic properties of the starting complex and in doing so it translates the initial problem to a simpler instance. We show that among such properties is that of area rigidity, a generalization of graph rigidity, and that every triangulation of a surface with small genus is area rigid. For arbitrary surfaces we initiate a statistical study of the behavior of algebraic shifting, and in turn of area rigidity. We show that asymptotically almost surely the algebraic shifting of a random Delaunay triangulation of any given closed Riemannian surface is concentrated in a simplicial complex that depends only on the genus and the number of vertices. This talk is based on joint works with Eran Nevo and Yuval Peled.
LOVE 13/11/2025 Characterizing NC1 with Typed Monoids, par Aidan Evans
Aidan Evans, University of Cambridge  
Salle B107, bâtiment B, Université de Villetaneuse
13/11/2025    10:30 - 12:00
Résumé :
Krebs et al. (2007) gave a characterization of the complexity class TC0 as the class of languages recognized by a certain class of typed monoids. The notion of typed monoid was introduced to extend methods of algebraic automata theory to infinite monoids and hence characterize classes beyond the regular languages. We advance this line of work beyond TC0 by giving a characterization of NC1 . This is obtained by first showing that NC1 can be defined as the languages expressible in an extension of first-order logic using only unary quantifiers over regular languages. The expressibility result is a consequence of a general result showing that finite monoid multiplication quantifiers of higher dimension can be replaced with unary quantifiers in the context of interpretations over strings, which also answers a question of Lautemann et al. (2001). We establish this collapse result for a much more general class of interpretations using results on interpretations due to Boja?czyk et al. (2019), which may be of independent interest.
LOCAL 06/11/2025 From Semantics to Syntax: A Type Theory for Comprehension Categories, par Niyousha Najmaei
Niyousha Najmaei, LIX  
Salle B107, bâtiment B, Université de Villetaneuse
06/11/2025    11:00 - 12:00
Résumé :
Recent models of intensional type theory have been constructed in algebraic weak factorization systems (AWFSs). AWFSs give rise to comprehension categories that feature non-trivial morphisms between types; these morphisms are not used in the standard interpretation of Martin-Löf type theory in comprehension categories. We develop a type theory that internalizes morphisms between types, reflecting this semantic feature back into syntax. Our type theory comes with ?-, ?-, and identity types. We discuss how it can be viewed as an extension of Martin-Löf type theory with coercive subtyping, as sketched by Coraglia and Emmenegger. We furthermore define semantic structure that interprets our type theory and prove a soundness result. Finally, we exhibit many examples of the semantic structure, yielding a plethora of interpretations.
AOC 06/11/2025 Aircraft routing: periodicity and complexity, par Frédéric Meunier
Frédéric Meunier  
Salle D215, Université de Villetaneuse
06/11/2025    10:30 - 12:00
Résumé :
The aircraft routing problem is one of the most relevant problems of operations research applied to aircraft management. It involves assigning flights to aircraft while ensuring regular visits to maintenance bases. This work examines two aspects of the problem. First, we explore the relationship between periodic instances, where flights are the same every day, and periodic solutions. The literature has implicitly assumed without discussion that instances necessitate periodic solutions, and even periodic solutions in a stronger form, where every two airplanes perform either the exact same cyclic sequence of flights, or completely disjoint cyclic sequences. However, enforcing such periodicity may eliminate feasible solutions. We prove that, when regular maintenance is required at most every four days, there always exist periodic solutions of this form. Second, we consider the computational hardness of the problem. Even if many papers in this area refer to the NP-hardness of the aircraft routing problem, such a result is only available in the literature for periodic instances. We establish its NP-hardness for a non-periodic version. Polynomiality of a special but natural case is also established. Joint work with Axel Parmentier and Nour ElHouda Tellache
CALIN 04/11/2025 Higher dimensional floorplans and Baxter permutations, par Thomas Muller
Thomas Muller, LIPN, Université Sorbonne Paris Nord  
Salle B107, bâtiment B, Université de Villetaneuse
04/11/2025    14:00 - 17:00
Résumé :
A 2-dimensional mosaic floorplan is a partition of a rectangle by other rectangles with no empty rooms. These partitions (considered up to some deformations) are known to be in bijection with Baxter permutations. A d-permutation is a (d-1)-tuple of permutations. In this talk, I will present a work in collaboration with Nicolas Bonichon and Adrian Tanasa where we introduce the d-floorplans which generalise the mosaic floorplans to arbitrary dimensions. I will first present the construction of their generating tree for which the corresponding labels and rewriting rules appear to be significantly more involved in higher dimensions. Then, I will present a bijection between the 2^{d-1}-floorplans and d-permutations characterised by forbidden vincular patterns, generalizing the bijection with Baxter permutations in the case d=2. Finally, I will present some work in progress on the "segments" of the 2^{d-1}-floorplans which relate d-floorplans to another class of d-permutations.
CALIN 21/10/2025 Statistical geometry and the Goldberg conjecture, par Fortuné Massamba
Fortuné Massamba, University of KwaZulu-Natal  
Salle B107, bâtiment B, Université de Villetaneuse
21/10/2025    14:00 - 17:00
Résumé :
Information geometry is an interdisciplinary field that uses the tools of differential geometry to explore and analyze probability theory and statistics. It focuses on statistical manifolds, geometric spaces (Riemannian manifolds) whose points represent different probability distributions. This geometric perspective provides powerful insights into many fields among which information theory. In this talk, I will present basic ideas about how to connect geometry and statistics, in particular statistical manifolds and their Fisher metric. Finally, closer to my current research themes, a statistical approach is discussed through the introduction of dual affine connections associated with the metric on almost Kähler manifolds. This research is motivated by the Goldberg conjecture, which asserts that a compact symplectic manifold (M,w) endowed with an w-compatible Einstein metric is Kähler.
LOCAL 21/10/2025 T-structures — entre logique et topologie, par Mathieu Anel
Mathieu Anel, CMU  
Salle B107, bâtiment B, Université de Villetaneuse
21/10/2025    10:30 - 12:00
Résumé :
Les structures de troncation, ou t-structures, ont été inventées pour remplacer les troncations de Postnikov en homotopie stable. Les modalités ont été inventées en théorie homotopique des types pour axiomatiser les troncations de Postnikov dans les ?-topos. Il se trouve que les deux notions peuvent s’encoder de manière uniforme comme des systèmes de factorisation stables par changement de base. Les examples de modalités abondent : préfaisceaux séparés, morphismes acycliques, A1-localisation, l’élusive modalité de Sullivan... J’expliquerai comment toute modalité vient avec une tour de complétion et comment on peut généraliser la notion de n-topos en t-topos, relatif à une modalité arbitraire.
SAFER 21/10/2025 Formal Verification of Systems with Unbounded Agents, par Tephila Prince
Tephila Prince, Indian Institute of Technology Dharwad  
https://bbb.lipn.univ-paris13.fr/b/ola-2wl-jir-a0l
21/10/2025    10:15 - 11:15
Résumé :
Client-server systems are a computing paradigm where work loads are distributed by the service providers called servers to the service requesters called clients. In case of a server handling an unbounded number of clients, how does one formally verify such systems? A first approach is to perform bounded model checking on it. Typically, in Bounded Model Checking (BMC), we find errors by examining all possible behaviours of the system for a specific temporal property up to some bounded number of steps. In case of unbounded client-server systems, the standard BMC approach does not suffice. What does one do when both the number of steps and the number of agents are unbounded? How do we choose a suitable model that captures true concurrency in the system? How do we specify the system properties in a suitable logic? In the first half of the talk, we focus on an extension to BMC to verify such unbounded client-server systems and also discuss the verification tool that employs SMT solvers. In the second half of the talk, we extend the idea of verification of systems with unbounded agents modeled using higher order Petri Nets called Elementary Object Systems (EOSs). We will present some decidability results for EOSs and a prototype to verify Petri Nets and EOSs using Answer Set Programming.
AOC 16/10/2025 The neighborhood dominant polytope, par Yue Zhang
Yue Zhang  
Salle B107, bâtiment B, Université de Villetaneuse
16/10/2025    10:30 - 12:00
Résumé :
We propose a new polyhedral approach for combinatorial optimization problems. Rather than working on the convex hull of the feasible set, we focus on a polytope that excludes the uninteresting feasible solutions dominated in a local neighborhood. In this work, the idea is applied to the linear Knapsack problem and the quadratic MaxCut problem with a theoretical study that demonstrates dominance inequalities and facets. The outstanding effectiveness of the proposed inequalities is numerically shown on the MaxCut instances from the BiqBin library.
LOCAL 09/10/2025 A Fibrational Approach to Differential Linear Logic, par Jad Koleilat
Jad Koleilat, LoCal  
Salle B107, bâtiment B, Université de Villetaneuse
09/10/2025    10:30 - 12:00
Résumé :
Differential Linear Logic (DiLL) is a sequent calculus expressing differentiation through symmetries between linear and non-linear formulas. In this talk, we express categorical models of DiLL as a pair of Grothendieck fibrations equipped with a tangent functor. To do so, we adapt methods from categorical semantics of Type Theory to linear-non-linear adjunctions. In the future, we hope this approach will enable the construction of models of a flavor of dependent differential linear logic.
CALIN 07/10/2025 Maximal number of subword occurrences in a word, par Wenjie Fang
Wenjie Fang, LIGM (en délégation CNRS au LIPN)  
Salle B107, bâtiment B, Université de Villetaneuse
07/10/2025    14:00 - 17:00
Résumé :
We consider the number of occurrences of subwords (non-consecutive sub-sequences) in a given word. We first define the notion of subword entropy of a given word that measures the maximal number of occurrences among all possible subwords. We then give upper and lower bounds of minimal subword entropy for words of fixed length in a fixed alphabet, and also showing that minimal subword entropy per letter has a limit value. A better upper bound of minimal subword entropy for a binary alphabet is then given by looking at certain families of periodic words. We also give some conjectures based on experimental observations.
AOC 02/10/2025 Scheduling Quantum Applications on Quantum Chips, par Francesco Contu
Francesco Contu  
Salle A303, bâtiment A, Université de Villetaneuse
02/10/2025    10:30 - 12:00
Résumé :
In this work we study the problem of scheduling quantum applications (i.e. quantum circuits) on shared quantum chips. Quantum computers are constrained by limited qubit connectivity and noisy operations, which makes the scheduling of quantum circuits on physical hardware a critical step for efficient execution. In this work, we model the scheduling problem as a tiling problem, under a set of assumptions that capture the main architectural restrictions of quantum chips. To address this problem, we propose an integer linear programming (ILP) formulation and present preliminary computational results.
CALIN 30/09/2025 Iterated Grafting Operators and Preferential Attachment Graph Models, par Francis Durand
Francis Durand  
Salle B107, bâtiment B, Université de Villetaneuse
30/09/2025    14:00 - 17:00
Résumé :
In this talk I will introduce the framework of iterated grafting operators, an operator-based model for generating and analyzing combinatorial structures. This formalism naturally connects to partial differential equations and to the normal ordering problem in operator algebras, and provides powerful tools for enumeration. The combinatorial study of these objects was initiated by Blasiak and Flajolet in Philippe Flajolet's last article Combinatorial Models of Creation-Annihilation, but many aspects remain unexplored. I will then focus on two specific models of preferential attachment graphs that arise from this approach. For these models, I will explain how to extract asymptotics from the associated generating functions using analytic techniques. Finally, I will discuss bijective correspondences with these graphs and open perspectives for random generation.
AOC 25/09/2025 New formulations and algorithms for the optimal classification tree problem, par Zacharie Ales
Zacharie Ales, SEMINAIRE AOC  
Salle B107, bâtiment B, Université de Villetaneuse
25/09/2025    10:30 - 12:00
Résumé :
Classification trees are models that provide highly interpretable classifiers but generally do not perform as well as neural networks. To obtain classifiers that are both interpretable and performant, we consider the problem of computing an optimal classification tree for a given data set. To address this problem, we first define new mathematical formulations in the form of mixed integer linear programs (MILP) and demonstrate that they are stronger and more efficient than state-of-the-art MILPs. To handle larger datasets, we then define iterative algorithms based on a data partition that is refined throughout the iterations.
LOCAL 25/09/2025 Réduction et induction rentrent dans un bar, par Jacopo Furlan
Jacopo Furlan, LoCal  
A303
25/09/2025    10:30 - 12:00
Résumé :
Le séminaire propose une discussion autour de l’opérateur de bar-récursion, son utilisation pour réaliser l’axiome du choix et le lien avec des propriétés très connues au sein de la théorie des algèbres booléennes. On présentera d’abord l’opérateur informellement, en une introduction historique sur sa première définition et sa ressemblance opérationnelle avec le principe de bar-induction. De suite, on abordera la notion de clôture pour une algèbre de Boole, une propriété fondamentale dans le cadre du forcing. On terminera en décrivant la connexion entre l’opérateur et cette propriété dans le cas de la réalisabilité classique, ce qui vient d’un travail avec Laura Fontanella.
CALIN 23/09/2025 The 3-state Potts model on planar maps, par Hadrien Notarantonio
Hadrien Notarantonio, IRIF, Paris  
Salle B107, bâtiment B, Université de Villetaneuse
23/09/2025    14:00 - 19:00
Résumé :
We consider the 3-state Potts generating function $T(\nu, w)$ of planar triangulations; that is, the series in $\nu$ and $w$ counting planar triangulations with vertices coloured in $3$ colours, weighted by their size and by the number of monochromatic edges (variable $\nu$). This series was proved to be algebraic $15$ years ago: this follows from its link with the solution of a discrete differential equation (DDE), and from general algebraicity results on such equations. However, despite recent progresses on the effective solution of DDEs, the exact value of had remained unknown so far. We have determined at last this exact value, proving that $T(\nu, w)$ satisfies a polynomial equation of degree $11$ in $T$. From this we determine the critical value of $\nu$ and the associated exponent. Another approach, applied to the heavier case of general planar maps (still $3$-coloured) yields an equation of degree $22$. Joint work with Mireille Bousquet-Mélou (LaBRI, Bordeaux)
LOCAL 11/09/2025 Oles Embeddings, par Paul Blain Levy
Paul Blain Levy, University of Birmingham  
Salle B107, bâtiment B, Université de Villetaneuse
11/09/2025    10:30 - 12:00
Résumé :
Oles embeddings are a way of generalizing the notion of injection in the category of sets (and decidable subobject in an extensive category) to an arbitrary category with finite coproducts. The concept is dual to that of Oles expansions, also known as very well-behaved lenses, which have played a role in the semantics of state. We also introduce notions of Oles inverse image square, Oles intersection square and union, generalizing the corresponding notions from the category of sets and satisfying several of their properties. We then further generalize these notions to the setting of a category acting on another category, and we see various examples from the semantics of effects arising as special cases. These include the lookup/update algebras (mnemoids) of Plotkin and Power, and monads supporting exceptions and other kinds of handling.
AOC 10/07/2025 Parametric polyhedra in mixed-integer programming, par Diego Morán Ramírez
Diego Morán Ramírez, Rensselaer Polytechnic Institute (prof invité)  
Salle B107
10/07/2025    10:30 - 11:30
Résumé :
We present some old and new results on arbitrary families of parametric polyhedra. First, if the constraint matrix is fixed, in the literature there are structural results for the integer hull and the finiteness of cutting plane closures for varying r.h.s. For instance, recently, Becu et al. proved in "Approximating the Gomory Mixed-Integer Cut Closure Using Historical Data" that the GMI closure of this family is finitely generated, in the sense that there exists a finite list of aggregation weights defining the GMI cuts that give the GMI closure for any polyhedra in the family. We extend this result for other cutting plane closures. Second, if the family of parametric polyhedra is arbitrary but all polyhedra in the family have the same integer hull, they define the same MIP, and we can leverage this information to understand and solve MIPs better. These families have been used to understand theoretical properties of the rank of cutting planes and to obtain better formulations. We present an application of these same-integer-hull families to formulations for the Asymmetric Traveling Salesman Problem.
AOC 07/07/2025 Deep Dual-Optimal Inequalities for Generalized Capacitated Fixed-Charge Network Design Problems, par Alexis Schneider
Alexis Schneider  
Salle B107
07/07/2025    10:30 - 11:30
Résumé :
Capacitated fixed-charge network design problems and generalizations, such as service network design problems, have a wide range of applications but are known to be very difficult to solve. Many exact and heuristic algorithms to solve these problems rely on column-and-row generation (CRG), which frequently suffer from primal degeneracy. We present a set of dual inequalities, equivalent to a simple primal relaxation, that speed up CRG algorithms for generalized capacitated fixed charge network design problems. We investigate the impact of the dual inequalities theoretically as well as experimentally. For practical applications, the presented technique is simple to implement, has no additional computational cost and can accelerate CRG by orders of magnitude, depending on the problem size and structure.
AOC 19/06/2025 A double ALNS metaheuristic for the multi-commodity location-network design problem with selection of heterogeneous vehicles, par Francesco Contu
Francesco Contu, Università degli Studi di Cagliari  
Salle A303
19/06/2025    10:30 - 11:30
Résumé :
This work investigates a decision support system for planning a consolidation-based distribution system in a city where inbound freight arrives in containers at an intermodal terminal. Since this facility lacks storage and transdock capabilities, containers must be transferred to satellite facilities to be unpacked and reloaded onto smaller vehicles. The problem is approached from the perspective of an urban mobility manager, who must select the satellite facilities and vehicles, define their routes, and determine the commodity flows to final destinations, while optimizing transportation resources. The problem is formulated as a Mixed-Integer Linear Programming model. To address realistically sized instances, a metaheuristic based on two Adaptive Large Neighborhood Searches (ALNSs) is proposed: the outer ALNS selects satellites and vehicles, and assigns containers to satellites; the inner ALNS handles routing and allocation decisions on the second echelon. These procedures are run iteratively. The metaheuristic is used to conduct an extensive experimental campaign using data from the city of Cagliari (Italy) to evaluate the distribution system.
LOCAL 19/06/2025 Anatomie d’un langage de programmation : la genèse du langage Prolog entre Marseille et Edimbourg (1970-1975), par Mathilde Fichen
Mathilde Fichen, CNAM  
Salle B107, bâtiment B, Université de Villetaneuse
19/06/2025    10:30 - 12:00
Résumé :
La philosophie des sciences éclaire la nature complexe des langages de programmation (dichotomie syntaxe/sémantique (White, 2004) ou fonction/structure (Turner, 2014)). Ces cadres d’analyse sont utiles mais insuffisants pour saisir pleinement leur complexité socio-technique, historiquement évolutive et socialement située. Le langage de programmation Prolog offre un cas d’étude particulièrement intéressant. Contrairement à d’autres langages l’ayant précédé (FORTRAN, COBOL, ALGOL ou encore LISP), Prolog n’est pas conçu de manière descendante à partir de spécifications techniques et d’un champ applicatif, mais émerge de manière itérative à partir d’un outil de démonstration automatique, dans le cadre de recherches menées sur le langage naturel par le Groupe d’Intelligence Artificielle de l’Université de Marseille Luminy au début des années 1970. Cette genèse particulière rend difficile la détermination d’un moment précis d’apparition du langage et nous amène à nous interroger sur les caractéristiques permettant de qualifier un système informatique particulier de langage de programmation. À travers trois tableaux, nous chercherons à montrer que le statut épistémique de Prolog est pluriel et intimement lié au contexte social de production et d’utilisation du langage. En suivant ainsi pas à pas la genèse de Prolog entre Marseille et Edimbourg, nous mettrons en lumière certains aspects méconnus des débuts de la recherche en intelligence artificielle en Europe au début des années 1970, de ses rivalités et de ses controverses.
CALIN 17/06/2025 Sur la complexité abélienne des mots infinis, par Idrissa Kaboré
Idrissa Kaboré, UNB - Université Nazi Boni  
Salle B107, bâtiment B, Université de Villetaneuse
17/06/2025    14:00 - 15:00
Résumé :
La complexité abélienne est un outil combinatoire qui calcule le nombre de vecteurs de Parikh de longueur donnée d'un mot infini. On appelle vecteur de Parikh d'un mot fini le vecteur formé par les nombres d'occurrences des lettres dans ce mot. Cette complexité a connu une étude intensive depuis son introduction formelle par Richomme et al en 2009. Dans cet exposé nous présenterons les fonctions de complexité de certains mots classiques (mots sturmiens, mots de Thue-Morse, mot de Tribonacci, ...) et quelques propriétés générales.
LOCAL 12/06/2025 A Fresh Inductive Approach to Useful Call-by-Value, par Mariana Milicich
Mariana Milicich, IRIF  
Salle B107, bâtiment B, Université de Villetaneuse
12/06/2025    10:30 - 12:00
Résumé :
Useful evaluation is an optimised evaluation mechanism for functional programming languages, introduced by Accattoli and Dal Lago. The key to useful evaluation is to represent programs with sharing and to implement substitution of terms only when this contributes to the progress of the computation. Initially defined in the framework of call-by-name, useful evaluation has since been extended to call-by-value. The definitions of usefulness in the literature are complex and lack inductive structure, which makes it challenging to (formally) reason about them. This talk focuses on an inductive notion of useful call-by-value. Our starting point is the well-known Value Substitution Calculus, refining its substitution operation so that it becomes linear, yielding the LCBV calculus. We then further refine LCBV by restricting linear substitution only when it contributes to the progress of the computation, yielding the UCBV strategy. This new substitution notion is sensitive to the surrounding evaluation context, so it is non-trivial to capture it inductively. Furthermore, the UCBV strategy can be implemented by an existing lower-level abstract machine called GLAMoUr with polynomial overhead in time. This entails, as a corollary, that UCBV can be implemented with polynomial time-overhead by invariant cost models. UCBV is part of the preliminary work required to develop semantic interpretations of useful call-by-value, for which its inductive formulation is more suitable than the (non-inductive) existing ones.
CALIN 10/06/2025 Analyse d'un algorithme probabiliste d'apprentissage par renforcement pour la recherche de plus courts chemins sur un graphe, par Zoé Varin
Zoé Varin, LaBRI, Université de Bordeaux  
Salle B107, bâtiment B, Université de Villetaneuse
10/06/2025    14:00 - 16:00
Résumé :
On étudie un processus d'apprentissage par renforcement, pour la recherche de plus courts chemins dans un graphe, dans lequel des fourmis partent d'un nid (aléatoire, N1 ou N2) et font une marche aléatoire (pondérée par les poids des arêtes) jusqu'à une source de nourriture F. À leur retour, elles renforcent les arêtes (en ajoutant 1 à leur poids) appartenant au chemin aller auquel on a enlevé les boucles inutiles. Ce modèle a déjà été étudié sur divers graphes dans le cas où le nid est déterministe, notamment les graphes séries-parallèles, mais aussi pour d'autres politiques de renforcements (articles de Kious, Mailler et Schapira). Nous étudions le cas à deux nids, dans des graphes obtenus en joignant trois graphes séries-parallèles pour former un triangle. On montre que les poids des arêtes (normalisés) convergent, vers des variables aléatoires nulles si et seulement si les arêtes associées n'appartiennent pas à un plus court chemin d'un sommet de {N1 , N2 , F } à un autre. Nous présenterons plusieurs outils utiles pour prouver cette convergence, notamment la comparaison avec des processus d'urnes, et quelques résultats sur les approximations stochastiques. La présentation se basera sur un travail en commun avec Cécile Mailler.
LOCAL 05/06/2025 Local state classifier for automata theory, par Ryuya Hora
Ryuya Hora, University of Tokyo  
Salle B107, bâtiment B, Université de Villetaneuse
05/06/2025    10:30 - 12:00
Résumé :
The notion of a local state classifier was introduced in the context of Lawvere's first open problem in topos theory. Although this problem itself has already been resolved, the idea of local state classifiers—defined as colimits of all monomorphisms—has potential applications in more general categorical frameworks beyond topos theory. In this talk, I will not delve into the technical details of topos theory. Instead, I will focus on explaining the definition and core idea of the local state classifier through simple examples. At the end of the presentation, I will briefly introduce my research on a topos-theoretic approach to automata theory, which is based on the fact that the local state classifier of the category of word actions PSh(?*) is given by word congruences.
LOCAL 22/05/2025 Operational Game Semantics in Type Theory, par Peio Borthelle
Peio Borthelle, Université Savoie Mont Blanc  
Salle B107, bâtiment B, Université de Villetaneuse
22/05/2025    10:30 - 12:00
Résumé :
Operational Game Semantics (OGS) is a flexible method for building models for open terms based on their operational semantics. After motivating and giving a high-level overview of an OGS model, I will present the most important constructions from my PhD thesis. This will encompass: - a high-level axiomatization of abstract machines, used to build a (reasonably) language-generic OGS model, - a practical representation for programming with games and their strategies in intensional type theories such as Rocq, based on coinduction, - a high-level proof of the soundness of our generic OGS model w.r.t. contextual equivalence.
CALIN 20/05/2025 Slit-Slide-Sew bijection for planar maps with prescribed degrees, par Juliette Schabanel
Juliette Schabanel, LaBRI  
Salle B107, bâtiment B, Université de Villetaneuse
20/05/2025    14:00 - 15:00
Résumé :
During the last 20 years, integrable hierarchies (KP/Toda) have proven to be a great source of recurrence formulas for maps of all kinds. However, most of those formulas still lack a bijective explication. In this talk, we provide a bijective proof for the planar case of Louf's formula, which counts bipartite planar maps with prescribed face degrees and arises from the Toda hierarchy. We actually show that his formula hides two simpler formulas, both of which can be rewritten as natural equations on trees using duality and Schaeffer's bijection for eulerian maps. The underlying bijection for trees can also be interpreted directly on bipartite maps as " slit-slide-sew " operations. As far as we know, this is the first bijection for a formula arising from an integrable hierarchy with infinitely many parameters.
CALIN 13/05/2025 Énumération des séquences d’inversions qui évitent des motifs, par Benjamin Testart
Benjamin Testart, Loria, Université de Lorraine  
Salle B107, bâtiment B, Université de Villetaneuse
13/05/2025    14:00 - 16:00
Résumé :
Une séquence d'inversions (ou table d'inversions) est une suite finie d'entiers (s_1, ..., s_n) telle que chaque terme s_i vérifie 0 ? s_i < i. Dans cet exposé, je présenterai différentes manières de construire ces séquences, qui permettent de les compter lorsqu'elles évitent des motifs. Je parlerai en particulier de constructions par "arbre de génération" et de quelques généralisations possibles de cette approche. Enfin, je donnerai un bref aperçu d'un travail en cours qui montre l'algébricité des fonctions génératrices des séquences d'inversions évitant certains ensembles de motifs.
A3 09/05/2025 owards Explainability for Interaction Network Analysis, par Maria Malek
Maria Malek  
Salle B107, bâtiment B, Université de Villetaneuse
09/05/2025    13:00 - 14:00
Résumé :
Explainability is increasingly recognized as a critical component of machine learning, enabling a wide range of stakeholders—including data scientists, domain experts, managers, and end users—to understand, trust, and effectively use model outputs. This talk explores the development of explainability approaches tailored to interaction network analysis, where meaningful insights often emerge from both topological structures and contextual information. We propose approaches that combine these complementary sources to generate deeper, more actionable explanations—particularly valuable in decision-support contexts. Two use cases illustrate our approach: (1) explainable sentiment analysis, integrating sentiment data with complex network structures, and (2) an explainable graph-based recommender system using a multimodal Graph Neural Network (GNN) architecture. We conclude by discussing key challenges and open questions related to the deployment of adaptive explainable systems in complex, real-world environments. Particular emphasis is placed on the potential of hybrid (neuro-symbolic) learning and the incorporation of domain ontologies to enhance interpretability in interaction network tasks.
A3 09/05/2025 Un étude des méthodes de pré-entrainement pour l'apprentissage incrémental par classe, par Eva Feillet.
Eva Feillet., Université Paris-Dauphine  
Salle B107, bâtiment B, Université de Villetaneuse
09/05/2025    12:00 - 13:00
Résumé :
L'apprentissage continu vise à intégrer, de manière adaptative, de nouvelles données à un modèle. Dans cette présentation, nous nous intéresserons au cas de l'apprentissage continu d'une classification d'images dans le cadre de l'apprentissage incrémental par classe "sans exemplaire" (exemplar-free class-incremental learning, EFCIL). Dans ce cadre, on considère un flux de données composé de lots correspondant à des ensembles disjoints de classes. L'objectif est d'entrainer, de manière itérative, un modèle à reconnaître un nombre croissant de classes, sans accès aux données passées. En effet, dans une perspective de confidentialité et/ou de frugalité, on part du principe que les données d'entrainement ne sont pas stockées de manière cumulative, d'où le terme d'apprentissage incrémental ? sans-exemplaire ?. Nous aborderons l'EFCIL sous l'angle du pré-entrainement des modèles, à travers deux études présentées à la conférence WACV. La première étude (Petit et al. 2024) propose de modéliser l'influence de la méthode de pré-entraînement, de l'algorithme EFCIL, du jeu de données et de la précision initiale sur la performance de divers modèles profonds dans le cadre de l'EFCIL. Nous verrons que le choix des stratégies de pré-entraînement a une plus grande influence sur la précision du modèle que le choix de l'algorithme EFCIL. En revanche, nos résultats montrent que l'algorithme EFCIL a une plus grande influence sur l'oubli des modèles (l'oubli étant calculé comme une perte de précision sur les classes apprises dans le passé). La deuxième étude s'intéresse plus particulièrement aux algorithmes d'EFCIL reposant sur des prototypes de classe (voir Feillet et al., 2025). Ces algorithmes, s'appuyant sur un encodeur fixe, tirent parti de modèles pré-entraînés pour entraîner de manière incrémentale un classifieur, tout en présentant un coût de calcul inférieur à celui d'un réglage fin (fine-tuning). Nous comparerons les stratégies de pré-entraînement en fonction de l'algorithme, du type d'image (réelles ou synthétiques) et de la quantité de données utilisées pour pré-entraîner l'encodeur. Nous discuterons de manière nuancée de l'utilité des différentes méthodes de pré-entrainement dans le cadre de l'EFCIL, suivant la quantité et le domaine des données d'intérêt, afin de fournir des recommandations pratiques permettant de faciliter la mise en place de l'apprentissage incrémental.
CALIN 06/05/2025 Polytopal realisations of finite arc complexes using strip deformations, par Pallavi Panda
Pallavi Panda, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
06/05/2025    14:00 - 15:00
Résumé :
Resume: A marked surface S is a finite-type possibly non-orientable surface with finitely many marked points (P) on the boundary and in the interior. These surfaces have long been studied both from a combinatorial as well as a geometric perspective. When the Euler characteristic of S\P is negative, the surface admits a finite-area hyperbolic metric. Such surfaces are called crowned surfaces, because their boundaries resemble a crown with spikes. Associated to marked/crowned surfaces is a combinatorial and topological object called the arc complex. This is a simplicial complex generated by arcs whose endpoints lie on the marked points. The arc complex has been used to understand the geometry of the surface by various mathematicians like Penner, Harer, Bowditch, Epstein. The arc complex is almost always infinite. In this talk we will focus on four families of surfaces for which it is finite. We will discuss how the topology of this complex helps us to understand certain deformations of crowned surfaces that weakly increase the "distances between spikes". As a result we get the non-simple polytopal realisations of these finite simplicial complexes. This is based ont the joint work with François Guéritaud. https://arxiv.org/abs/2505.01285
LOCAL 26/04/2025 Compléxité des topos pour la logique linéaire : une analyse socio-philosophique (en Coq), par Sergueï Lenglet
Sergueï Lenglet  
Bobigny
26/04/2025    14:00 - 23:00
Résumé :
Ce séminaire exceptionnel, qui devrait intéresser absolument tous les membres de l'équipe LoCal, se déroulera dans un cadre original. Dans une première partie, nous présenterons les topos pour la logique linéaire en transportant des meubles d'un appartement balbynien dans un monospace. Dans une deuxième partie, nous analyserons la complexité de ces structures en transvasant ces mêmes meubles de ce même monospace dans un appartement idéalement situé à côté de Gare du Nord. Enfin, nous discuterons de la pertinence de notre approche socio-philosophique au cours d'un apéro dinatoire composé de bières et de pizzas (voire de vodkas) (en Coq)
LOCAL 10/04/2025 Modal semantics without possible worlds, par Renato Reis Leme
Renato Reis Leme, Unicamp  
Salle B107, bâtiment B, Université de Villetaneuse
10/04/2025    10:30 - 12:00
Résumé :
In 1981, J. Kearns published 'Modal Semantics Without Possible Worlds' [1], in which he developed a semantics based on non-deterministic matrices for the modal logics KT, S4, and S5. Despite being an interesting alternative to the standard semantics, it does not provide a decision procedure. This problem remained open until recently, when L. Grätz [2] found a solution for KT and S4. Building on an extension of Kearns' semantics for modal logic K [3], we are now extending this solution to the entire normal modal cube. [1] Kearns, John T. "Modal semantics without possible worlds." The Journal of Symbolic Logic 46.1 (1981): 77-86. [2] Grätz, Lukas. "Truth tables for modal logics T and S4, by using three-valued non-deterministic level semantics." Journal of Logic and Computation 32.1 (2022): 129-157. [3] Omori, Hitoshi, and Daniel Skurt. "More modal semantics without possible worlds." IfCoLog Journal of Logics and their Applications 3.5 (2016): 815-846.
AOC 10/04/2025 Quantum algorithms for optimization, par Camille Grange
Camille Grange  
Salle G201
10/04/2025    10:30 - 11:30
Résumé :
Quantum computation is a new paradigm that is increasingly being exploited today for designing methods to solve optimization problems. Although its application to numerical instances is limited, among other reasons due to the lack of quantum RAM, theoretical advantages are emerging compared to classical approaches for several classes of problems. In this talk, we provide insights into what makes quantum algorithms powerful for optimization and illustrate it with a new bounded-error quantum-classical algorithm. Specifically, this algorithm combines the generalization of Grover Search with dynamic programming to polynomially reduce the worst-case time complexity of NP-hard minimization problems satisfying certain properties. We exemplify it on several scheduling problems.
CALIN 08/04/2025 Expressing properties of finite automata in variants of first-order logic, par Howard Straubing
Howard Straubing, Boston College  
Salle B107, bâtiment B, Université de Villetaneuse
08/04/2025    13:00 - 14:00
Résumé :
** Warning ** : the seminar will take place at 1pm, as it is merged with the seminar of the complexity axis that usually take place during lunch time. This is a survey of research going back more than 60 years on the power of first order logic, along with various restrictions and extensions, to express the behavior of finite automata operating on strings over a finite alphabet. 'Restrictions and extensions' here means modifying the set of atomic formulas, bounding the quantifier depth, bounding the number of bound variables, etc. We want to be able to determine when a particular property (given in some other formalism, for example by a finite automaton) is expressible in the variant of first-order logic under study. When the atomic formulas are restricted in such a way that only regular languages can be defined, there is an intricate mathematical apparatus, based in the algebraic theory of finite semigroups, that provides very precise answers to these questions. This will be the subject of the first part of the talk. There are strong connections, known since the 1980's, between this theory and questions about the complexity of fixed depth circuit families whose gates have unbounded fan-in. This, along with a few other extensions (for example, to automata operating on trees) and some recent results and open probems, will be explored in the second part of the talk.
A3 27/03/2025 Fouille de motifs fréquents dans les graphes : l'essor de l’apprentissage profond et des architectures neuronales, par Assaad ZEGHINA
Assaad ZEGHINA, Chercheur contractuel, Icube, Université de Strasbourg  
Salle B107, bâtiment B, Université de Villetaneuse
27/03/2025    12:00 - 13:00
Résumé :
L’utilisation de méthodes d’apprentissage automatique et apprentissage profond pour résoudre des problèmes jusque-là abordés par des techniques classiques suscite un intérêt grandissant, en particulier lorsqu’il s’agit de données massives et hétérogènes. Parmi ces problématiques, l’extraction de motifs fréquents dans les graphes spatio-temporels soulève de nombreux défis : la multiplicité des types d’arcs, la prise en compte simultanée des facteurs spatiaux et temporels, ainsi que la complexité combinatoire de l’énumération de sous-graphes récurrents. Les méthodes traditionnelles, souvent basées sur des approches d’exploration exhaustive, peinent à passer à l’échelle et à préserver des performances satisfaisantes quand la taille du graphe augmente ou que sa structure devient plus riche. Dans ce contexte, deux approches basées sur l’apprentissage automatique et l’apprentissage profond sont présentées pour répondre aux enjeux d’efficacité et d’évolutivité liés à l’extraction de motifs dans de grands graphes. La première, Multi-SPMiner, étend les capacités de l’extraction de motifs aux multigraphes et intègre un Multigraph Convolution Network. Cette architecture de réseau de neurones permet de projeter simultanément les nœuds et leurs voisinages dans un espace latent, tout en maintenant la structure hiérarchique des sous-graphes. Divers raffinements—dont l’incorporation de mécanismes d’attention—améliorent la capture des interactions complexes et la robustesse face aux données manquantes. La seconde méthode, Deep-QMiner, recourt à l’apprentissage par renforcement profond multi-agents pour reformuler l’exploration des graphes en une suite de décisions séquentielles. Cette approche rend possible une navigation plus dynamique et sélective parmi les sous-graphes potentiels, permettant de limiter l’explosion combinatoire typique des algorithmes d’exploration exhaustive. Les performances de ces deux méthodes ont été évaluées à la fois sur des jeux de données synthétiques et sur des données réelles, notamment issues des données environnementales. Les expériences montrent que Multi-SPMiner et Deep-QMiner peuvent traiter des graphes d’une taille allant jusqu’à 2000 nœuds et identifier des motifs dont la taille varie de 4 à 10 nœuds, tout en conservant une efficacité de calcul et une précision élevée. Les résultats soulignent également une capacité de généralisation marquée : un entraînement initial sur données synthétiques ne dégrade pas significativement les performances lors d’une application ultérieure à des jeux de données réels. En définitive, ces travaux illustrent le potentiel des approches neuronales et de l’apprentissage par renforcement pour faire face aux défis liés à la complexité et à la diversité des graphes, ouvrant la voie à de nombreuses applications dans des domaines aussi variés que les systèmes intelligents de transport, la biologie des réseaux ou la compréhension des dynamiques territoriales.
AOC 27/03/2025 Fine-grained complexity of reachability problems on different temporal graph models, par Guillaume Aubian
Guillaume Aubian  
Salle C213
27/03/2025    10:30 - 11:30
Résumé :
Temporal graphs model interactions evolving over time, with different representations depending on how time is taken into account: several models coexist, notably the point model and the interval model. Although these two models are often considered equivalent in discrete time, switching from one to the other can have major implications in terms of computational complexity. In this talk, I'll describe how we proved fundamental complexity discrepancies between these two models for classical problems such as computing the fastest time path (minimizing the total travel time) and the shortest time path (minimizing the number of edges). I will also explain how, while the computation of the fastest time path can be solved in quasi-linear time in the point model, it requires quadratic time in the interval model under standard complexity assumptions. However, a quasi-linear time algorithm exists in the interval model with zero path times. Interestingly, we found no such discrepancy for the global temporal connectivity problem, for which we proved a valid quadratic lower bound in both models, corresponding to the known upper bounds. These results shed new light on the computational limits of temporal graphs and the impact of the choice of time representation. This is joint work with Filippo Brunelli, Feodor F. Dragan, Guillaume Ducoffe, Michel Habib, Allen Ibiapina and Laurent Viennot.
LOCAL 26/03/2025 Effects in Skel. From Exceptions to Delimited Computation, par Alan Schmiit
Alan Schmiit, I.N.R.I.A.  
Salle B107, bâtiment B, Université de Villetaneuse
26/03/2025    14:00 - 15:00
Résumé :
Skeletal Semantics is a meta-language to describe the semantics of programming languages. We present it through several examples, highlighting how complex features can be captured in a readable way using monads. These features range from simple effects like exceptions to more complex ones like generators.
CALIN 25/03/2025 Unified study of block-weighted planar maps: combinatorial and probabilistic properties, par Zéphyr Salvy
Zéphyr Salvy, TU Wien  
Salle B107, bâtiment B, Université de Villetaneuse
25/03/2025    14:00 - 15:00
Résumé :
This talk focuses on classes of planar maps with a weight u>0 on certain components called *blocks*. In collaboration with Fleurat, we study the decomposition of generic planar maps into 2 -connected components, revealing a phase transition between the universality classes of maps (converging to the Brownian sphere) and plane trees (converging to the Brownian tree), depending on the value of u . We identify a new class with the stable tree of parameter 3/2 as the scaling limit in the critical case, and obtain precise results on block sizes in each phase. In a subsequent work, I show that it is possible to study many decomposition schemes along similar lines to shed light on a phase transition. I explain how to obtain enumerative results, block sizes and scaling limits for each phase. Finally, with Albenque and Fusy, we studied tree-rooted random planar maps decomposed into tree-rooted 2 -connected blocks, where a spanning tree is drawn simultaneously with the map. This model, which is of interest in theoretical physics, shows new behaviours. We determine the asymptotic behaviour of 2 -connected tree-rooted maps, reveal a phase transition, and study the properties of each phase.
A3 20/03/2025 Détection de communautés disjointes : une nouvelle méthode basée sur ?-similarité structurell, par Motaz ben hassine
Motaz ben hassine, Enseignant-chercheur contractuel à l'Université d'Artois  
Salle B107, bâtiment B, Université de Villetaneuse
20/03/2025    12:00 - 14:00
Résumé :
L'analyse des réseaux sociaux est un domaine largement étudié en intelligence artificielle et très sollicité dans de nombreuses applications du monde réel. Par exemple, la détection de communautés permet d’identifier un public cible en marketing digital, d’améliorer les systèmes de recommandation, etc. Les approches existantes pour la détection de communautés reposent souvent sur des méthodes agglomératives exploitant des mesures de similarité basées sur les voisins communs. Dans ce contexte, une approche a été proposée, qui ne se limite pas au voisinage en commun, mais prend également en compte la sémantique des interactions entre les voisins en commun.
AOC 20/03/2025 Nash bargaining solution for bi-objective combinatorial optimization, par Minh Hieu Nguyen
Minh Hieu Nguyen, ENSTA  
Salle C213
20/03/2025    10:30 - 11:30
Résumé :
Bi-objective combinatorial optimization (BOCO) arises in many real-world scenarios where a decision-maker (DM) must simultaneously optimize two conflicting objectives. BOCO poses significant challenges due to the discrete nature of the decision space and the inherent trade-offs between the objectives. Existing methods for BOCO can be broadly categorized into a posteriori methods, which explore the Pareto front comprehensively, and a priori methods, for which DM's preferences are defined beforehand and incorporated in the optimization phase. While a posteriori methods offer a variety of trade-off solutions, a priori methods are often preferred in practice due to their computational efficiency and compatibility with the decision-making process. Cooperative game theory and multi-objective optimization intersect in finding acceptable solutions amidst conflicting goals. The concepts in bargaining games are well-suited for solving multi-objective optimization problems because both involve resolving trade-offs among competing interests (players or objectives). In convex multi-player bargaining problems, the Nash Bargaining Solution (NBS), a fundamental concept introduced by Nash, offers a powerful framework for balancing multiple objectives by ensuring fairness and mutual benefit for the parties involved. Although the concept has been generalized for non-convex bargaining problems, there has been limited application of the NBS in multi-objective optimization, particularly in BOCO. Motivated by this gap, in this research, we aim to consider the NBS as a criterion for selecting preferred solutions within the Pareto front of BOCO. In multi-player bargaining problems, the NBS maximizes the product of the players' gains over their disagreement outcomes. In the BOCO context, the NBS maximizes the product of the objectives relative to a reference point, which can be chosen as the Nadir point. Notice that the Nadir point is obtained by computing each objective with the optimal decision vector of the other objective. Along with Utopia point, which is the (unfeasible) point where both objectives take maximum values, they are crucial for understanding the trade-offs between two objectives and guiding the decision-making process. For our purpose, we consider a more general version of the NBS in BOCO by incorporating the DM's point of view. Specifically, we introduce the generalized NBS (rho-NBS) where rho > 0 is a parameter reflecting the DM's priority to the first objective compared to the second one. Thus, the rho-NBS maximizes the product of the power rho of the first objective and the second objective relative to the Nadir point. It is important to note that the problem of maximizing the product of two functions, even when they are linear with binary variables, is NP-hard. In this research, we focus on identifying the rho-NBS within the set of supported efficient solutions instead of the whole Pareto front. These supported efficient solutions are located on the convex hull of the Pareto front and offer valuable insights into its structure in BOCO. We first introduce the rho-NBS concept for BOCO. Then, we develop a binary search algorithm to identify the rho-NBS within the set of supported efficient solutions. To the best of our knowledge, this is the first application of the Nash bargaining game to multi-objective combinatorial optimization, where an efficient algorithm has been developed. Finally, we apply our theory and algorithm to the Bi-Objective Assignment Problem (BOAP), a specific example of BOCO.
LOCAL 20/03/2025 Grothendieck topologies on a free monoid, par Morgan ROGERS
Morgan ROGERS, LoCal, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
20/03/2025    10:30 - 11:30
Résumé :
Toposes are often motivated by presenting the special case of sheaves on a topological space. In general, a (Grothendieck) topos is constructed from a `site' consisting of a category equipped with a `Grothendieck coverage', so-called because in the motivating case the category involved is the partially ordered set of opens of a topological space and the coverage consists of the coverings of one open by its open subsets. In other words, the best-studied special case of sites are those where the underlying category is a poset. At the other extreme, when the underlying category is a monoid, a Grothendieck coverage becomes instead a collection of ideals closed under certain operations. In this talk we explain different ways in which the data of a Grothendieck coverage on a *free* monoid can be expressed, we explain how this is related to Cantor space(s) and to a certain equivalence relation on infinite words. Finally, we explain how this fits into our work on continuous actions of topological monoids (which some colleagues have already seen me talk about).
AOC 13/03/2025 Decision-focused learning: theory and applications to contextual stochastic optimization, par Thibault Prunet
Thibault Prunet, CERMICS, École des Ponts  
Salle B107
13/03/2025    10:30 - 11:30
Résumé :
Real-world industrial applications frequently confront the task of decision-making under uncertainty. The classical paradigm for these complex problems is to use both machine learning (ML) and combinatorial optimization (CO) in a sequential and independent manner. ML learns uncertain quantities based on historical data, which are then used used as an input for a specific CO problem. Decision-focused learning is a recent paradigm, which directly trains the ML model to make predictions that lead to good decisions. This is achieved by integrating a CO layer in a ML pipeline, which raises several theoretical and practical challenges. In this talk, we aim at providing a comprehensive introduction to decision-focused learning. We will first introduce the main challenges raised by hybrid ML/CO pipelines, the theory of Fenchel-Young losses for surrogate differentiation, and the main applications of decision-focused learning. As a second objective, we will present our ongoing works that aim at developing efficient algorithms based on the Bregman geometry to address the minimization of the empirical regret in complex stochastic optimization problems.
A3 06/03/2025 Intelligent Facilitation of Deliberation in Online Debates, par Caren Al Anaissy
Caren Al Anaissy, Post-doc LIP6  
Salle B107, bâtiment B, Université de Villetaneuse
06/03/2025    12:00 - 14:00
Résumé :
Deliberative processes are crucial for forming opinions, decisions, and policies within society. Unlike persuasive debates, deliberation seeks to enhance the understanding of conflicting perspectives among stakeholders. Online debate platforms provide a space where users can create debates, argue for or against specific topics by posting pro/con arguments, and vote on othersÂ’ arguments. Online collective discussions play an important role in enhancing the participants critical thinking, understanding the public opinion, they can help participants rationalise their thoughts in controversial topics and reduce the spread of fake news. While these discussions generate valuable insights, they also present challenges. Reading through all arguments requires a considerable amount of time, some discussions might shift from a topic to another and some arguments might even be maliciously used to spread fake news. Understanding the outcome of a debate would be beneficial for different stakeholders. Artificial Intelligence (AI) offers promising solutions to moderate and curate such debates, provided it operates in an intelligible and accountable manner. In this talk, I will present my ongoing project on facilitating deliberation in online debates. The project focuses on developing an AI-based system that interacts directly with participants to help them navigate and engage effectively in the discussion. This system will also provide explanations for its predictions about the debateÂ’s outcome, based on the userÂ’s moves. By offering insights into the possible outcomes of their choices and interactions, the system not only enhances participants' understanding of the debate but also empowers them to contribute more efficiently.
AOC 06/03/2025 Designing sustainable diet plans by solving tri-objective 0-1 programs, par Marianna De Santis
Marianna De Santis, Università degli Studi di Firenze (prof invitée)  
Salle C212
06/03/2025    10:30 - 11:30
Résumé :
We present an algorithm for triobjective nonlinear integer programs that combines the eps-constrained method with available oracles for biobjective integer programs. We prove that our method is able to detect the nondominated set within a finite number of iterations. Specific strategies to avoid the detection of weakly nondominated points are devised. The method is then used to determine the nondominated solutions of triobjective 0-1 models, built to design nutritionally adequate and healthy diet plans, minimizing their environmental impact. The diet plans refer to menus for school cafeterias and we consider the carbon, water and nitrogen footprints as conflicting objectives to be minimized. Energy and nutrient contents are constrained in suitable ranges suggested by the dietary recommendation of health authorities. Results obtained on two models and on real world data are reported and discussed. Coauthors: Luca Benvenuti, Alberto De Santis, Daniele Patria
LOCAL 06/03/2025 Polymorphic Reachability Types: Tracking Freshness, Aliasing, and Separation in Higher-Order Generic Programs, par Guannan Wei
Guannan Wei, ANTIQUE, ENS  
Salle B107, bâtiment B, Université de Villetaneuse
06/03/2025    10:30 - 12:00
Résumé :
Fueled by the success of Rust, many programming languages are adding substructural features to their type systems. The promise of tracking properties such as lifetimes and sharing is tremendous, not just for low-level memory management, but also for controlling higher-level resources and capabilities. But so are the difficulties in adapting successful techniques from Rust to higher-level languages, where they need to interact with other advanced features, especially various flavors of functional and type-level abstraction. In this talk, I will present reachability types, a recent proposal has shown promise in scaling lifetime reasoning to higher-order and polymorphic settings, tracking aliasing and separation on top of a substrate inspired by separation logic. More specifically, I will present the simply-typed ??-calculus with precise lightweight (i.e., quantifier-free) reachability polymorphism, and the F<:?-calculus with bounded parametric polymorphism over types and reachability qualifiers. I will present meta-theory results, safe capability programming patterns enabled by reachability types, and flow-sensitive effect system extensions. If time permits, I will also discuss recent ongoing developments of reachability types.
CALIN 04/03/2025 Combinatoire énumérative et bijective de différentes familles de chemins de Dyck avec trous d'air , par Rémi Maréchal
Rémi Maréchal, GREYC, UNICAEN, Caen  
Salle B107, bâtiment B, Université de Villetaneuse
04/03/2025    14:00 - 16:00
Résumé :
Cet exposé se situe dans le cadre de la combinatoire des chemins sur réseau. On introduit ici une généralisation des chemins de Dyck (dits "avec trous d'air"), avant de se pencher sur diverses questions classiques à leur sujet : énumération, distributions de motifs, étude de sous-ensembles, etc. Ce faisant, des suites d'entiers positifs (connues dans la littérature) apparaissent naturellement. Dès que possible, on cherchera alors à relier les objets combinatoires décrits par ces suites aux chemins de Dyck avec trous d'air, à travers des bijections explicites. Les travaux présentés ont été effectués pendant mon doctorat, et correspondent à trois publications dont les co-auteurs sont Jean-Luc Baril, Sergey Kirgizov, Helmut Prodinger, et Vincent Vajnovszki.
LOCAL 27/02/2025 Applied Synthetic Computability Theory: Gödel's Incompleteness Theorem and Post's Problem, par Dominik Kirst
Dominik Kirst, IRIF  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2025    10:30 - 12:00
Résumé :
Traditionally, computability theory is based on a notion of computable functions induced by concrete models like Turing machines, lambda calculus, or general recursion. While these models are well-studied, they only provide a somewhat secondary explanation of computability, at times obscuring the simple computational essence of abstract constructions and constituting a notorious burden for mechanisation in a proof assistant. In this talk, I will give an overview of synthetic computability theory as introduced by Richman and Bauer, offering an elegant alternative: at the price of giving up on some principles of classical reasoning, computability becomes a primitive notion, even internalisable by the axiom that every function is computable. After discussing this general framework in the context of constructive mathematics, I will describe some recent work on Gödel's incompleteness theorem and Post's problem, both developed synthetically in constructive type theory and mechanised in the Coq proof assistant.
CALIN 25/02/2025 Alternating normal form in the standard braid monoid: local characterization, minimal automaton and automaticityTitre bientôt disponible, par June Roupin
June Roupin, LIGM  
Salle B107, bâtiment B, Université de Villetaneuse
25/02/2025    14:00 - 16:00
Résumé :
A braid can be seen as an equivalence class of words, and choosing a unique word representing each braid helps computing braids, motivating the study of normal forms. In the standard braid monoid, two such normal forms are the Garside normal form, which cuts a braid into a sequence of small simple braids, and the alternating normal form, which consists of recursively splitting a braid into a sequence of braids using less strands. The Garside normal form has many useful properties, in particular forming a regular and automatic language, as well as having a simple local characterization. On the other hand, only the regularity of the alternating normal was known. I will describe a new local characterization of the alternating normal form, explicitly construct its minimal automaton, and give some intuitions regarding its automaticity.
CALIN 18/02/2025 Kissing polytopes, par Antoine Deza
Antoine Deza  
Salle B107, bâtiment B, Université de Villetaneuse
18/02/2025    14:00 - 16:00
Résumé :
A lattice (d,k)-polytope is the convex hull of a set of points in dimension d whose coordinates are integers ranging between 0 and k. We investigate the smallest possible distance between two disjoint lattice (d,k)-polytopes. This question arises in various contexts where the minimal distance between such polytopes appears in complexity bounds of optimization algorithms. We provide nearly matching lower and upper bounds for this distance and propose an algebraic model. Our formulation yields explicit formulas in dimensions 2 and 3, and allows for the computation of previously intractable values. Based on joint-work with Shmuel Onn (Technion), Sebastian Pokutta (Zuse Institute Berlin), and Lionel Pournin (Université Paris 13).
LOCAL 13/02/2025 Reusable resources analysis by abstract machines for high-level languages, par Hector Suzanne
Hector Suzanne, LIP6, Sorbonne Université  
Salle B107, bâtiment B, Université de Villetaneuse
13/02/2025    10:30 - 12:00
Résumé :
Static resource analysis is dedicated to finding methods determining the quantify of resources (time, energy, memory, ...) required to run a program, together with the variables this quantity depends on. The cornerstone of this endeavour is finding invariants/variants between program states: an analyser must automatically understand the algorithms encoded into the program without programmer input. We will focus on resource analyses through type systems for functional languages. To this aim, we introduce AutoBill, an abstract machine used as intermediate representation for functional languages for resource analysis, both for monotone (energy, time) and non-monotone (memory, money) resources. We compile to this machine, amongst others, an ML-style language with data-structures (ADT), recursion (fixpoints), and some further extensions. AutoBill uses Call-by-Push-Value operational semantics, which mixes call-by-value and call-by-name, to encode the runtime semantics of functional languages. The use of an abstract machine furthermore allows continuations to be encoded as explicit call stacks. This in turns enables the re-use of data structures analyses to analyse control flow within programs. On top of our machine, a so-called polarized linear type system makes explicit the flow of resources that accompanies jumping in and out of computations. Those types are enriched with natural integer parameters, that are controlled during type-checking through the addition of equations and constraints to data-type definitions. This enables the approximating sizes, costs, combinatorial invariant, etc. in a first-order constraint. This is done during type-inference, and provides a link between those quantities and the largest resource usage occurring at runtime. The constraint is then sent to an SMT solver for validation, or to a linear programming optimizer to generate polynomial resource bounds. We implement the "Automated Amortized Resource Analysis" method in AutoBill. It assigns, to each data-structure, a count of the amount of sub-structures which relevant shapes. This is then used to bounds the iteration counts of an algorithm and obtain polynomial worst-case complexities. This implementation consists of a specialized compilation scheme from a source language to the abstract machine. The typing-and-analysis engine is then independent of both the source language and the chosen analysis method.
AOC 06/02/2025 A probing-enhanced stochastic programming approach for the capacitated multi-item lot-sizing problem., par Franco Quezada
Franco Quezada, Universidad de Santiago de Chile & ENSTA  
Salle B107
06/02/2025    10:30 - 11:30
Résumé :
In traditional stochastic programming, decisions are made based on known probabilities or distributions of uncertain parameters. However, in real-world scenarios, decision-makers often have opportunities to gather additional information about these uncertainties through a process known as probing. Probing allows for observation of certain random variables, which can provide valuable insights into the behavior of related uncertainties. However, probing is not free—it involves a cost that must be taken into account in the decision-making process. This cost could represent financial expenditure, time, or resource allocation necessary to gather data or perform exploratory actions. Thus, probing involves taking actions or gathering data to learn more about the uncertain variables before making the final decision. In two-stage stochastic programs, this can mean performing certain preliminary actions (probing decisions) that help to reveal more information about future states (first and second-stage decisions). We investigate a probing-enhanced stochastic programming approach for the two-stage stochastic multi-item capacitated lot-sizing problem, which is a classic inventory management problem where decisions are made in two stages to minimize costs while considering uncertain future demand. Two-stage problems, except for very simple models, are generally intractable to solve exactly. Even with complete knowledge of the demand distribution, explicitly integrating the second-stage costs is computationally prohibitive. A common approach to address this complexity is the Sample Average Approximation (SAA) method, which approximates the expectation by sampling from the original distribution to create a finite set of scenarios. Then we adopt a non-anticipative formulation that enables us to ensure that decisions are consistent with the information available at the time of decision-making. The critical aspect of this approach is that the enforcement of non-anticipativity conditions depends on the decisions themselves. Thus, the resulting model includes a vast number of conditional non-anticipativity constraints, proportional to the square of the number of scenarios. This leads to a mixed-integer linear programming (MILP) formulation characterized by a large number of big-M constraints, which can be challenging to solve efficiently. We propose a decomposition approach to solve the resulting non-anticipative formulation, exploiting the structure of the problem by breaking it into smaller, more manageable sub-problems that can be solved efficiently, providing a more practical and scalable solution approach. Preliminary computational results demonstrate that the proposed decomposition algorithm significantly outperforms the other approaches in terms of both solution quality and computation time, achieving improvements by several orders of magnitude. Joint work with Céline Gicquel, Safia Kedad-Sidhoum and Bernardo Pagnoncelli.
CALIN 28/01/2025 Online Prediction in Sub-linear Space, par Nabil Mustafa
Nabil Mustafa , LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
28/01/2025    14:00 - 17:00
Résumé :
In this talk, I will present the main ideas from this paper: Online Prediction in Sub-linear Space, B. Peng and F. Zhang, SODA 2023 (best student paper award). It gives new low-space algorithms for the regret minimisation problem in learning theory. Precious little is required in the way of prerequisites, except that you be intelligent enough to be interested in this sort of thing. The talk will start from the basics (the experts problems), and then cover the new ideas to entend classical learning algorithms to work, approximately, with sub-linear space.
RCLN 27/01/2025 Titre bientôt disponible, par Nesrine Bannour
Nesrine Bannour, Institut Imagine  
Salle B107, bâtiment B, Université de Villetaneuse
27/01/2025    12:30 - 13:30
Résumé :
à paraître
A3 23/01/2025 Quantification d'Incertitude en Apprentissage Automatique, par Arthur Hoarau
Arthur Hoarau  
Salle B107, bâtiment B, Université de Villetaneuse
23/01/2025    12:00 - 14:00
Résumé :
La quantification d'incertitude est un vaste domaine dépassant celui de l'intelligence artificielle. À la frontière entre mathématiques et informatique, l'objectif est de modéliser et quantifier l'incertitude d'une source. D'abord, pour ce qui est des labels (étiquettes attribuées aux observations en classifciation), ils sont souvent obtenus auprès d'humains et il est parfois plus intéressant de modéliser l'incertitude dans les labels en entrée plutôt que de récolter des labels bruités, qui vont dégrader les performances des modèles. La difficulté réside donc dans le fait de modéliser au mieux ces labels. Ensuite, l'incertitude du modèle lui-même est cruciale pour toutes les taches suivantes (prédiction, prise de décision, apprentissage incrémental/actif...). L'hésitation du modèle peut s'avérer informative et de nombreuses techniques peuvent être appliquées pour modéliser cette incertitude, sous différentes formes. Comprendre et expliquer la prédiction d'un modèle fait partie des grands défis de l'intelligence artificielle.
LOVE 23/01/2025 Game comonads for existential and positive equivalence, par Thomas Laure
Thomas Laure, Equipe MoLoToV, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
23/01/2025    10:30 - 12:00
Résumé :
Les jeux de comparaison de modèles, tels que le pebble game ou le jeu d'Ehrenfeucht-Fraïssé sont une approche très riche en théorie des modèles. Un point de vue structurel sur ces jeux est donné par la notion de game comonad, qui permet de capturer la question de la préservation entre deux structures relationnelles d'un fragment de la logique du premier ordre, avec une "ressource" finie, par l'existence de certains morphismes dans une catégorie de coalgèbres. On présentera les idées générales de ces game comonads, et on illustrera les premiers résultats de préservation. Des variantes des jeux correspondent à des fragments logiques plus petits, comme le fragment existentiel positif, relativement plus simple. On étudie le fossé entre ce fragment et le fragment complet, en considérant d'une part le fragment existentiel et d'autre part le fragment positif, pour déterminer comment interviennent séparément la négation (atomique) et les quantificateurs universels. Enfin, si on a un peu de temps, on présentera succinctement les idées des arboreal categories, conçues pour axiomatiser ces catégories de coalgèbres et unir tous les résultats pour les différents jeux en un seul.
CALIN 21/01/2025 Laplace's and Cauchy's contributions to the Stirling partition number, par Hsien-Kuei Hwang
Hsien-Kuei Hwang , Institute of Statistical Science  
Salle B107, bâtiment B, Université de Villetaneuse
21/01/2025    14:00 - 15:00
Résumé :
Pierre-Simon Laplace (1749-1827) is widely recognized for his monumental works, Théorie analytique des probabilités and Mécanique céleste. Augustin-Louis Cauchy (1789-1857), on the other hand, revolutionized classical operational analysis by formalizing it with a rigorous foundation, laying the groundwork for modern calculus and complex analysis. However, their contributions to the Stirling partition numbers remain largely overlooked in the combinatorial literature, a gap this talk aims to address. By examining their lesser-known work on Stirling partition numbers through a historical lens and integrating modern methodological perspectives, the presentation highlights the intersection of their insights with the combinatorial framework of Stirling numbers, offering new appreciation for their contributions to this area of mathematics. This research is based on ongoing joint work with Chong-Yi Li and Vytas Zacharovas.
A3 16/01/2025 Synergies between machine learning and reasoning, par Smail Baaj
Smail Baaj, MAÃŽTRE DE CONFÉRENCES EN INFORMATIQUE  
Salle B107, bâtiment B, Université de Villetaneuse
16/01/2025    12:00 - 14:00
Résumé :
Aujourd'hui, l'accent est mis sur le développement de points de rencontre entre les deux principaux domaines de recherche de l'Intelligence Artificielle (IA) : l'apprentissage et le raisonnement. Outre la recherche de synergies et de complémentarités, un approfondissement de la recherche en représentation des connaissances et raisonnement et en matière d'apprentissage automatique est souhaité, ainsi que des moyens par lesquels les paradigmes de ces domaines pourraient interagir. Des discussions récentes ont mis en avant le besoin de développer un cadre qualitatif unifié qui permet à la fois un apprentissage de type “neuronal” et un raisonnement de type logique. Dans cette optique, nous distinguons deux problèmes d'apprentissage : l’apprentissage des paramètres des règles possibilistes qui permet de développer des approches neuro-symboliques basées sur la théorie des possibilités et l’apprentissage de capacités pour les intégrales de Sugeno couramment utilisées dans la théorie de la prise de décision multicritère. Nous montrons que ces deux problèmes d'apprentissage peuvent être formulés en termes de systèmes d'équations relationnelles floues. Plus précisément, on s'intéresse au développement d'outils pour traiter l'incompatibilité des systèmes d'équations relationnelles floues qui sont sous-jacents aux deux problèmes d'apprentissage avec des données réelles (qui peuvent être sujettes aux bruits et à des valeurs aberrantes). L'objectif est d'obtenir des solutions approchées des systèmes incompatibles s'appuyant sur des fondements théoriques solides.
AOC 16/01/2025 Decision aid for tactical transportation problems, par Guillaume Joubert
Guillaume Joubert  
Salle A303
16/01/2025    10:30 - 11:00
Résumé :
Due to the complexity of real-world planning processes addressed by major transportation companies, decisions are often made considering subsequent problems at the strategic, tactical, and operational planning phases. However, these problems still prove to be individually very challenging. This talk will present two examples of tactical transportation problems motivated by industrial applications: the Train Timetabling Problem (TTP) and the Service Network Scheduling Problem (SNSP). The TTP aims at scheduling a set of trains, months to years before actual operations, at every station of their path through a given railway network while respecting safety headways. The SNSP determines the number of vehicles and their departure times on each arc of a middle-mile network while minimizing the sum of vehicle and late commodity delivery costs. For these two problems, the consideration of capacity and uncertainty in travel times are discussed. We present models and solution approaches including MILP formulations, Tabu search, Constraint Programming techniques, and a Progressive Hedging metaheuristic.
LOVE 16/01/2025 Proofs as Terms and Terms as Programs, Positively, par Jui-Hsuan Wu
Jui-Hsuan Wu, LIX  
Salle B107, bâtiment B, Université de Villetaneuse
16/01/2025    10:30 - 12:00
Résumé :
Structural proof theory has been widely used in the study of term structures. In the first part of the talk, I will illustrate this tight connection between proofs and terms by presenting the focused proof system LJF as a framework for designing term structures. A key feature of LJF is that it does not fix a canonical polarization for atomic formulas, which leads to two different approaches to term representation: one in which atomic formulas are polarized negatively, and another in which they are polarized positively. In particular, these two approaches will be illustrated through the encoding of untyped lambda terms. When atomic formulas are given the negative polarity, LJF proofs yield the usual tree-like syntax of untyped lambda terms. In contrast, when atomic formulas are given the positive polarity, LJF proofs yield a syntax that allows for sharing via explicit substitution. In the second part of the talk, I will show how the syntax derived from the positive polarization can be used to define the positive lambda calculus, a call-by-value lambda calculus with explicit substitution. If time permits, I will also discuss how this calculus is closely related to the notion of usefulness thanks to its compactness.
RCLN 13/01/2025 Titre bientôt disponible, par Paul Lerner
Paul Lerner, LISN  
Salle B107, bâtiment B, Université de Villetaneuse
13/01/2025    12:15 - 13:30
Résumé :
Résumé à paraitre
AOC 09/01/2025 A Bi-level Approach for Last-Mile Delivery, par Maria Elena Bruni
Maria Elena Bruni, UniversitaÂ’ della Calabria - professeur invitée  
Salle B107, bâtiment B, Université de Villetaneuse
09/01/2025    10:30 - 11:30
Résumé :
Last-mile delivery is regarded as an essential, yet challenging problem in city logistics. One of the most common initiatives, implemented to streamline and support last-mile activities, are satellite depots. These intermediate logistics facilities are used by companies in urban areas to decouple last-mile activities from the rest of the distribution chain. Establishing a business model that considers different stakeholders' interests and balances the economic and operational dimensions, is still a challenge. In this seminar, we will introduce a novel problem that broadly covers such setting, where the delivery to customers is managed through satellite depots and the interplay and the hierarchical relation between the problem agents are modeled in a bi-level framework. Two mathematical models and an exact solution approach, properly customized for our problem, will be presented, and extensive computational experiments on benchmark instances and a real case study discussed. Finally, we will shed light on future research directions on how the proposed approach can be extended for other relevant problem classes.
LOVE 13/12/2024 Séminaire VE : Munyque Mittelman, par Munyque Mittelman
Munyque Mittelman  
Salle B107, bâtiment B, Université de Villetaneuse
13/12/2024    12:00 - 13:00
Résumé :
In recent years, a wealth of logic-based languages have been introduced to reason about the strategic abilities of autonomous agents in multi-agent systems (MAS), including Alternating-time Temporal Logic (ATL) and Strategy Logic (SL). These formalisms have been used to verify the correctness of a MAS, which is viewed as a yes/no matter: either the system satisfies the specification or it does not. Evaluating the quality of systems through Boolean satisfaction is often inadequate, as different levels of quality may exist. In this talk, we present recent extensions of ATL and SL with quantitative semantics, allowing us to capture different degrees of satisfaction. We then discuss how these formalisms can be applied to Mechanism Design and Incentive Engineering.
AOC 12/12/2024 Optimizing alphabet reduction pairs of arrays, par Sophie Toulouse
Sophie Toulouse, LIPN  
A303
12/12/2024    10:30 - 11:30
Résumé :
In a previous work, we introduced “alphabet reduction pairs of arrays” (ARPAs), a family of combinatorial designs, to transport differential approximation results for k-CSPs over an alphabet of size p ? k to k-CSPs over an alphabet ?q of size q > p. ARPAs on ?q consist of two arrays of q columns satisfying the following conditions: the first array must contain a certain word composed of all symbols of ?q; no row of the second array can involve more than p different symbols of ?q; the two arrays must coincide on any subset of k columns. In the context of approximation, the target word in the first array represents an optimal solution that the second array allows us to associate with assignments involving at most p different values. Thus, we want to maximize the frequency of this particular word, and refer to ARPAs that achieve this as “optimal”. To study optimal ARPAs, we consider a seemingly simpler family of combinatorial designs, called “Cover Pairs of Arrays” (CPAs), which can be viewed as a Boolean interpretation of ARPAs. The two arrays of a CPA still share the same number q of columns, and must match on any k of them; but they take Boolean entries, the second array is restricted to words with at most p ones, and we want to maximize the frequency of the word of q ones in the first array. Using combinatorics and linear programming, we establish the equivalence between ARPAs and CPAs in terms of maximizing the frequency of the target word. In addition, we provide optimal constructions for the case where k ? {1, 2, p}. These results establish the optimality of ARPAs given in previous work for the case where p = k, and highlight the relevance of CPAs for the approximability of k CSPs. They also raise new questions about ARPAs, which we will discuss along with other questions about related combinatorial designs that allow refining our knowledge of how well k-CSP-q reduces to k-CSP-p. Joint work with Jean-François Culus.
LOVE 10/12/2024 Coalition Strategy Logic: Model Checking et Completude, par Davide Catta
Davide Catta, LIPN  
Salle A303, LIPN
10/12/2024    14:00 - 15:00
Résumé :
Les logiques pour le raisonnement stratégique constituent une vaste famille d’outils formels conçus pour modéliser, vérifier et analyser les capacités et les stratégies (individuels ou collectifs) d’agents autonomes, dans un environnement compétitif. Nous introduisons Coalition Strategy Logic (CSL), qui combine les intuitions de Coalition Logic (CL) et de Strategy Logic (SL). Plus précisément, CSL permet une quantification arbitraire sur les actions de groupes d’agents. La motivation derrière CSL est double. Premièrement, nous montrons que CSL est strictement plus expressive que d’autres logiques de coalition connues, puis nous discutons de sa procédure de model checking. Deuxièmement, nous fournissons une axiomatisation cohérente et complète de cette logique, qui est, à notre connaissance, la première axiomatisation d’une logique stratégique dans la littérature.
A3 05/12/2024 Intelligent Facilitation of Deliberation in Online Debates, par Caren Al Anaissy
Caren Al Anaissy  
Salle B107, bâtiment B, Université de Villetaneuse
05/12/2024    12:15 - 13:30
Résumé :
Deliberative processes are crucial for forming opinions, decisions, and policies within society. Unlike persuasive debates, deliberation seeks to enhance the understanding of conflicting perspectives among stakeholders. Online debate platforms provide a space where users can create debates, argue for or against specific topics by posting pro/con arguments, and vote on othersÂ’ arguments. Online collective discussions play an important role in enhancing the participants critical thinking, understanding the public opinion, they can help participants rationalise their thoughts in controversial topics and reduce the spread of fake news. While these discussions generate valuable insights, they also present challenges. Reading through all arguments requires a considerable amount of time, some discussions might shift from a topic to another and some arguments might even be maliciously used to spread fake news. Understanding the outcome of a debate would be beneficial for different stakeholders. Artificial Intelligence (AI) offers promising solutions to moderate and curate such debates, provided it operates in an intelligible and accountable manner. In this talk, I will present my ongoing project on facilitating deliberation in online debates. The project focuses on developing an AI-based system that interacts directly with participants to help them navigate and engage effectively in the discussion. This system will also provide explanations for its predictions about the debateÂ’s outcome, based on the userÂ’s moves. By offering insights into the possible outcomes of their choices and interactions, the system not only enhances participants' understanding of the debate but also empowers them to contribute more efficiently.
AOC 05/12/2024 On the Computation of Strategyproof and Fair Picking Sequences, par Hugo Gilbert
Hugo Gilbert, Université Paris Dauphine - LAMSADE  
Salle G203
05/12/2024    11:00 - 12:00
Résumé :
When allocating indivisible items to agents, it is known that the only strategyproof mechanisms that satisfy a set of rather mild conditions are constrained serial dictatorships (also known as non-interleaving picking sequences): given a fixed order over agents, at each step the designated agent chooses a given number of items (depending on her position in the sequence). With these rules, agents who come earlier in the sequence have a larger choice of items. However, this advantage can be compensated by a higher number of items received by those who come later. How to balance priority in the sequence and number of items received is a nontrivial question. In this presentation, we use a model parameterized by a mapping from ranks to scores, a social welfare functional, and a distribution over preference profiles. For several meaningful choices of parameters, we show that an optimal sequence can be computed exactly in polynomial time or approximated by resorting to sampling. Joint work with Sylvain Bouveret, Jérôme Lang, and Guillaume Méroué.
LOVE 28/11/2024 Active Learning of Mealy Machines with Timers, par Gaëtan Staquet
Gaëtan Staquet  
Salle A303, bâtiment A, Université de Villetaneuse
28/11/2024    12:30 - 13:30
Résumé :
In order to understand and verify complex systems, we need accurate models that are either understandable for humans or can be analyzed fully automatically. Such models, however, are typically not available for legacy software. Active automata learning is a black-box technique for constructing state machine models of software and hardware components from information obtained through testing (i.e., providing inputs and observing the resulting outputs) and may thus fill this gap. In many applications, timing plays a crucial role, which in turn makes extending automata learning to a setting that incorporates quantitative timing information challenging. In this talk, we present an active learning algorithm for a general class of Mealy machines with timers (MMTs) in a black-box context. A Mealy machine is a finite state machine that outputs a sequence of symbols for every processed input word. We then augment it with timers that force certain transitions to occur after a certain amount of time has elapsed. Our algorithm is an extension of the L# algorithm of Vaandrager et al. [1] to a timed setting. Like the algorithm for learning timed automata proposed by Waga [2], our algorithm is inspired by ideas of Maler & Pnueli [3]. Based on the elementary languages of [3], both Waga's and our algorithm use symbolic queries, which are then implemented using finitely many concrete queries. However, whereas Waga needs exponentially many concrete queries to implement a single symbolic query, we only need a polynomial number. This is because in order to learn a timed automaton, a learner needs to determine the exact guard and reset for each transition (out of exponentially many possibilities), whereas for learning an MMT a learner only needs to figure out which of the preceding transitions caused a timeout. As shown in a previous work [4], this can be done efficiently for a subclass of MMTs that are “race-avoiding”: if a timeout is caused by a preceding input then a slight change in the timing of this input will induce a corresponding change in the timing of the timeout. [1]: Frits W. Vaandrager, Bharat Garhewal, Jurriaan Rot, and Thorsten Wißmann. A new approach for active automata learning based on apartness. TACAS 2022. [2]: Masaki Waga. Active learning of deterministic timed automata with myhill-nerode style characterization. CAV 2023. [3]: Oded Maler and Amir Pnueli. On recognizable timed languages. FOSSACS 2004. [4]: Véronique Bruyère, Guillermo A. Pérez, Gaëtan Staquet, and Frits W. Vaandrager. Automata with timers. FORMATS 2023.
AOC 28/11/2024 Benders Adaptive-Cuts Method for Two-Stage Stochastic Programs, par Eduardo Moreno
Eduardo Moreno, Universidad Adolfo Ibáñez, Santiago, Chile; Google Research, Paris, France  
Salle C314
28/11/2024    10:30 - 11:30
Résumé :
Two-stage stochastic programs (TSSP ) are a classic model where a decision must be made before the realization of a random event, allowing recourse actions to be performed after observing the random values. For example, many classic optimization problems, like network flows or facility location problems, became TSSP if we consider, for example, a random demand. Benders decomposition is one of the most applied methods to solve TSSP with a large number of scenarios. The main idea behind the Benders decomposition is to solve a large problem by replacing the values of the second-stage subproblems with individual variables, and progressively forcing those variables to reach the optimal value of the subproblems, dynamically inserting additional valid constraints, known as Benders cuts. Most traditional implementations add a cut for each scenario (multi-cut) or a single-cut that includes all scenarios. In this paper we present a novel Benders adaptive-cuts method, where the Benders cuts are aggregated according to a partition of the scenarios, which is dynamically refined using the LP-dual information of the subproblems. This scenario aggregation/disaggregation is based on the Generalized Adaptive Partitioning Method (GAPM). We formalize this hybridization of Benders decomposition and the GAPM, by providing sufficient conditions under which an optimal solution of the deterministic equivalent can be obtained in a finite number of iterations. Our new method can be interpreted as a compromise between the Benders single-cuts and multi-cuts methods, drawing on the advantages of both sides, by rendering the initial iterations faster (as for the single-cuts Benders) and ensuring the overall faster convergence (as for the multi-cuts Benders). Computational experiments on three TSSPs validate these statements, showing that the new method outperforms the other implementations of Benders method, as well as other standard methods for solving TSSPs, in particular when the number of scenarios is very large. Joint work with Ivana Ljubic (ESSEC Business School).
LOVE 28/11/2024 Parsing Correctness Criterion for Second Order Multiplicative Linear Logic, par Adrien Ragot
Adrien Ragot, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
28/11/2024    10:30 - 12:00
Résumé :
We introduce a method for defining a Parsing Correctness Criterion for Second-Order Multiplicative Linear Logic proof structures, where bounded variables are represented using pointers. A key insight in demonstrating the validity of this criterion is recognizing that a parsing sequence involving pointers can be viewed as a standard parsing sequence (without pointers), where a 'forall' link is contracted only if the 'exists' link it depends on has already been contracted. This illustrates how pointers store part of the sequentiality information, ensuring that 'exists' links are introduced before the corresponding 'forall' links. Moreover, the criterion is able to construct a sequent calculus proof from a parsing sequence, and because the parsing is confluent rewriting on proof nets and always decrease the size of a net the criterion runs in quadratic time.
A3 21/11/2024 L'AI Act quel impact sur l'enseignement et la recherche ?, par Marc Champesme
Marc Champesme  
Salle B107, bâtiment B, Université de Villetaneuse
21/11/2024    12:00 - 14:00
Résumé :
Depuis une dizaine d'années, face à la place de plus en plus grande prise dans la société par les services numériques, dont l'intelligence artificielle, la demande de régulation se fait de plus en plus forte dans le monde. Discriminations, atteintes à la vie privée, effets sur l'emploi et les conditions de travail, surveillance généralisée, dégradation de l'environnement, propagation de fake news et de discours de haine ... les alertes sont nombreuses. Le règlement européen sur l'IA (AI Act) est une des premières initiatives de régulation gouvernementale au niveau international. Le but de cette présentation est d'en décrire les principales caractéristiques en mettant un focus sur ces éventuelles incidences sur nos pratiques professionnelles d'enseignants et/ou chercheurs. Dans ce cadre, seront également abordées, brièvement, les préoccupations et revendications des organisations syndicales de l'enseignement et de la recherche au niveau mondial par le biais des positions prises par l'Internationale de l'Éducation (http://www.ei-ie.org).
AOC 21/11/2024 Robust approaches for the Kidney Exchange Problem, par Matteo Petris
Matteo Petris, ENPC  
Salle B107
21/11/2024    10:30 - 11:30
Résumé :
In the Kidney Exchange Problem (KEP), we consider a pool of altruistic donors and incompatible patient-donor pairs. Kidney exchanges can be modelled in a directed weighted graph as circuits starting and ending in an incompatible pair or as paths starting at an altruistic donor. The weights on the arcs represent the medical benefit which measures the quality of the associated transplantation. For medical reasons, circuits and paths are of limited length and are associated with a medical benefit to perform the transplants. The aim of the KEP is to determine a set of disjoint kidney exchanges of maximal medical benefit or maximal cardinality (all weights equal to one). In this work, we consider two types of uncertainty in the KEP which stem from the estimation of the medical benefit (weights of the arcs) and from the failure of a transplantation (existence of the arcs). Both uncertainty are modelled via uncertainty sets with constant budget. The robust approach entails finding the best KEP solution in the worst-case scenario within the uncertainty set. We modelled the robust counter-part by means of a max-min formulation which is defined on exponentially-many variables associated with the circuits and paths. We propose different exact approaches to solve it: either based on the result of Bertsimas and Sim or on a reformulation to a single-level problem. In both cases, the core algorithm is based on a Branch-Price-and-Cut approach where the exponentially-many variables are dynamically generated. The computational experiments prove the efficiency of our approach.
LOVE 20/11/2024 Security Analysis and Robust Supervisory Control of Discrete Event Systems, par Gaiyun Liu
Gaiyun Liu  
Salle A303, bâtiment A, LIPN
20/11/2024    12:00 - 13:00
Résumé :
This talk centers on both the theoretical and applied research aspects of discrete event systems (DESs). At the beginning, Dr. Liu will introduce her related research groups. The second part of the talk will cover the modeling, analysis, and supervisory control of DESs, using automated manufacturing systems as demonstrative examples. Dr. Liu's relevant achievements in Petri net structure theory and supervisory control based on time constraints will also be emphasized in this part. The third part introduces the robust/adaptive supervisory control of DESs. In case of failures, the existing control policies are always no longer in force. We have developed relevant theories of Petri nets and designed robust/adaptive supervisory controllers so that the system can run without deadlock regardless of failures. The fourth part concerns security analysis and resilient control of networked DESs. The existence of various types of network attacks makes the supervisory control design of networked DES a great challenge. Attacks may drive the originally well-controlled DES to an unsafe/illegal state covertly. We have done analysis of effectiveness and stealthiness of sensor attacks in labeled Petri nets. Also, we have designed resilient supervisors for labeled Petri nets under attacks. The talk summarizes Dr. LiuÂ’s recent research achievements and highlights future directions in this field.
AOC 14/11/2024 Filtering Pricing Subproblems in Dantzig-Wolfe decomposition, par Mathieu Lacroix
Mathieu Lacroix, LIPN  
Salle A303
14/11/2024    10:30 - 11:30
Résumé :
Column generation is used alongside Dantzig-Wolfe Decomposition, especially for linear programs having a decomposable pricing step requiring to solve numerous independent pricing subproblems. We propose a filtering method to detect which pricing subproblems may have improving columns, and only those subproblems are solved during pricing. This filtering is done by providing light, computable bounds using dual information from previous iterations of the column generation. The experiments show a significant impact on different combinatorial optimization problems.
LOVE 14/11/2024 A unified approach to Markov kernels and linear operators, par Pedro Azevedo de Amorim
Pedro Azevedo de Amorim, University of Oxford  
Salle B107, bâtiment B, Université de Villetaneuse
14/11/2024    10:30 - 11:30
Résumé :
In recent years, there has been much work done in probabilistic semantics. Most of them fall in one of two categories; those based on monads and those based on linear logic. At the semantic level, these two different semantics correspond to distinct basic programming abstractions. In this case, semantically, programming with monads corresponds to programming with Markov kernels, while linear logic corresponds to programming with linear operators. In this talk I will go over recent work of mine that tries to establish a formal connection between these two families of semantics. I will start by presenting a new core calculus for programming with Markov kernels and linear operators, will show that this formalism encompasses useful models from the probabilistic semantics literature and will conclude by sketching some applications of this formalism to the new research program of synthetic probability theory.
LOVE 07/11/2024 A recipe for the semantics of reversible programming , par Louis Lemonnier
Louis Lemonnier, University of Edinburgh  
Salle B107, bâtiment B, Université de Villetaneuse
07/11/2024    10:30 - 12:00
Résumé :
In this presentation, we explore the foundational elements required to interpret reversible programming within a categorical framework. We use the symmetric pattern-matching language introduced by Sabry, Valiron, and Vizzotto as a reference point, and we incorporate several improvements. We show that inductive data types and recursion can also be effectively modelled in this setting. However, these results do not straightforwardly extend to the pure quantum case. We provide insights into the challenges encountered and propose potential directions for addressing these limitations, for example with guarded recursion. (Self) references: Classical reversible semantics: https://doi.org/10.4230/LIPIcs.FSCD.2024.19 / https://arxiv.org/abs/2309.12151 First-order quantum semantics (chapter 3): https://theses.hal.science/tel-04625771 / https://arxiv.org/abs/2406.07216
AOC 07/11/2024 Binary Classifiers via Semi-definite Programming, par Benedetto Manca
Benedetto Manca, Università degli Studi di Cagliari  
Salle D214
07/11/2024    10:30 - 11:30
Résumé :
Abstract: Starting from the general proposal of Grzybowski et al. that defines the concept of separation of two finite point sets X and Y by means of a convex set S, we consider the case where S is the minimum volume ellipsoid that intersects the convex combinations of all pairs of points in X and Y. According to this separation rule it is possible to consider an ellipsoid S which contains one class and leave out the other one, or an ellipsoid that does not contain neither of the two classes but still separates them. These two cases can be used to define two binary classifiers whose fitting problems relies on the solution of different Semi-definite programs. In this seminar I will introduce both ellipsoidal binary classifiers together with the corresponding semi-definite programming and some algorithmic approaches to solve it more efficiently. Some numerical experiments will be also presented.
AOC 31/10/2024 New perspectives on invexity and its algorithmic applications, par Ksenia Bestuzheva
Ksenia Bestuzheva, ZIB  
Salle B107, bâtiment B, Université de Villetaneuse
31/10/2024    10:30 - 11:30
Résumé :
One of the key properties of convex problems is that every stationary point is a global optimum, and nonlinear programming algorithms that converge to local optima are thus guaranteed to find the global optimum. However, some nonconvex problems possess the same property. This observation has motivated research into generalizations of convexity. This talk proposes a new generalization which we refer to as optima-invexity: the property that only one connected set of optimal solutions exists. We state conditions for optima-invexity of unconstrained problems and discuss structures that are promising for practical use, and outline algorithmic applications of these structures.
A3 24/10/2024 Explaining AI Decisions: Approximate Formal Explanations for Classifiers Using Greedy Algorithms, par Louenas BOUNIA
Louenas BOUNIA, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
24/10/2024    12:15 - 13:15
Résumé :
Ce séminaire est consacré à l'Intelligence Artificielle Explicable (XAI), avec un focus particulier sur les explications formelles des classifieurs. Dans le contexte croissant de l'utilisation des systèmes d'IA dans des domaines critiques, il est devenu essentiel de rendre ces modèles explicables pour assurer la transparence, la confiance et l'interprétabilité des décisions qu'ils produisent. Dans ce séminaire, nous aborderons plus spécifiquement le problème de l'approximation des explications formelles pour les classifieurs. Calculer une explication abductive de taille minimale peut s'avérer une tâche très chronophage pour plusieurs raisons. D'une part, l'explosion combinatoire du nombre d'explications abductives rend la recherche de l'explication de taille minimale extrêmement coûteuse en temps. D'autre part, trouver une explication de taille minimale est souvent au moins problème NP-difficile, même pour des classifieurs restreints comme les arbres de décision (DP-complet pour les foréts aléatoires). Cela signifie que les approches exactes peuvent être très lentes, notamment pour des instances complexes ou des entrées de grande dimension. Face à ces défis, des approches approximatives ou heuristiques sont fréquemment employées pour réduire la charge computationnelle et obtenir des résultats plus rapidement, même si cela se fait au détriment de l'optimalité de la solution. Nous formulons le problème de la recherche d'une explication abductive de taille minimale pour une instance x, donnée un classifieur h, comme un problème de sélection d'un ensemble d'attributs leaders de taille minimale dans le cadre d'une fonction supermodulaire. Nous proposons un algorithme glouton avec des garanties d'approximation. Nos expérimentations montrent que, lorsque h est représenté par un arbre de décision ou une forêt aléatoire, notre algorithme constitue une alternative efficace aux méthodes exactes basées sur les encodages SAT, notamment dans le cas d'instances difficile.
LOVE 24/10/2024 Around Classical and Intuitionistic Linear Processes , par Jorge A. Pérez
Jorge A. Pérez, University of Groningen, The Netherlands.  
Salle B107, bâtiment B, Université de Villetaneuse
24/10/2024    10:30 - 12:00
Résumé :
Title: Around Classical and Intuitionistic Linear Processes (based on joint work with Juan C. Jaramillo and Dan Frumin, presented at CONCUR'24) Abstract: Curry-Howard correspondences between Linear Logic (LL) and session types provide a firm foundation for concurrent processes. As the correspondences hold for intuitionistic and classical versions of LL (ILL and CLL), we obtain two different families of type systems for concurrency. An open question remains: how do these two families exactly relate to each other? Based upon a translation from CLL to ILL due to Laurent, we provide two complementary answers, in the form of full abstraction results based on a typed observational equivalence due to Atkey. Our results elucidate hitherto missing formal links between seemingly related yet different type systems for concurrency.
LOVE 22/10/2024 Ordonnancement des tâches au sein des établissements de santé à l'aide des techniques d'intelligence artificielle, par Safia Bousalmi
Safia Bousalmi  
Salle A303, bâtiment A, Université de Villetaneuse
22/10/2024    16:00 - 17:00
Résumé :
Nous présenterons nos recherches récentes sur l'ordonnancement des tâches au sein des établissements de santé, un problème complexe d'affectation des patients aux chambres en respectant des contraintes strictes et souples. L’objectif principal de ce travail est de minimiser la somme des pénalités associées aux violations de contraintes souples, telles que les préférences des patients ou les propriétés spécifiques des chambres. Les contraintes strictes incluent l'attribution unique d'une chambre à chaque patient pour chaque nuitée, le respect de la capacité des chambres, ainsi que la correspondance du genre des patients avec celui des chambres. La complexité et l'interdépendance de ces contraintes rendent difficile la résolution du problème par des méthodes classiques. Dans ce cadre, nous explorons l’utilisation des techniques d’intelligence artificielle, en particulier les métaheuristiques. Ces méthodes bio-inspirées, telles que la métaheuristique de sélection clonale, permettent de générer des solutions optimisées tout en évitant les pièges des optima locaux, répondant ainsi aux besoins d'un environnement hospitalier complexe. Bien que nos simulations soient en cours, nous envisageons d’améliorer notre algorithme en intégrant les systèmes à événements discrets, soit pour modéliser les processus hospitaliers de manière plus précise, soit pour calculer des bornes inférieures, voire pour les deux. Cette intégration vise à affiner notre approche et à renforcer l'évaluation des solutions obtenues.
AOC 10/10/2024 Online policy selection for inventory problems, par Adeline Fermanian
Adeline Fermanian, Califrais  
Salle B107, bâtiment B, Université de Villetaneuse
10/10/2024    10:30 - 11:00
Résumé :
After a general presentation of the company Califrais and of research problems arising in food supply chain, we will focus on a recent work on online inventory problems. These are decision problems where at each time period the manager has to make a replenishment decision based on partial historical information in order to meet demands and minimize costs. To solve such problems, we build upon recent works in online learning and control, use insights from inventory theory and propose a new algorithm called GAPSI. This algorithm follows a new feature-enhanced base-stock policy and deals with the troublesome question of non-differentiability which occurs in inventory problems. Our method is illustrated in the context of a complex and novel inventory system involving multiple products, lost sales, perishability, warehouse-capacity constraints and lead times. Extensive numerical simulations are conducted to demonstrate the good performances of our algorithm on real-world data.
LOVE 10/10/2024 Les bronzés font des machines abstraites en HOcore, par Sergueï Lenglet
Sergueï Lenglet, LIPN  
Salle A303, bâtiment A, Université de Villetaneuse
10/10/2024    10:30 - 11:30
Résumé :
We present fully abstract encodings of the call-by-name lambda-calculus into HOcore, a minimal higher-order process calculus with no name restriction. We consider several equivalences on the lambda-calculus side---normal-form bisimilarity, applicative bisimilarity, and contextual equivalence---that we internalize into abstract machines in order to prove full abstraction.
RCLN 07/10/2024 Synthèse graphique multidimensionnelle : application aux documents hétérogènes, par Amal BELDI
Amal BELDI, USPN  
Salle B107, bâtiment B, Université de Villetaneuse
07/10/2024    12:15 - 14:00
Résumé :
L'intégration des données implique l'organisation et la consolidation harmonieuses de divers formats et structures de données, garantissant leur compatibilité pour une analyse approfondie L'analyse basée sur les graphes exploite des techniques avancées de modélisation de graphes pour découvrir des connexions et des motifs complexes au sein des ensembles de données, offrant ainsi des aperçus précieux pour la prise de décision. Les techniques de résumé de graphes visent à condenser des graphes de données complexes tout en préservant les informations essentielles, facilitant ainsi un traitement et une visualisation plus efficaces des données pour une compréhension et une interprétation améliorées. Nos objectifs sont les suivants : - Aborder l'hétérogénéité des données : se concentrer sur la synthèse de types de données variés, en particulier numériques et textuelles, pour gérer efficacement la diversité des formats, des structures et des représentations des données. - Personnaliser le résumé des données : c’est adapter le processus de synthèse pour répondre aux besoins spécifiques des utilisateurs, en veillant à ce que la consolidation des données soit à la fois pertinente et centrée sur l'utilisateur. - Mettre en œuvre un résumé sémantique : Développer une approche de synthèse qui se concentre principalement sur un cadre normalisé pour décrire les ressources, en intégrant des éléments sémantiques pour améliorer l'interconnexion et la signification des données.
CALIN 04/10/2024 Journées MathStic Probabilités-Combinatoire 2, par Michael Drmota, Alice Contat, Andrew Elvey Price, Enrica Duchi, Quentin Berger
Michael Drmota, Alice Contat, Andrew Elvey Price, Enrica Duchi, Quentin Berger  
Amphithéâtre Euler, Institut Galilée
04/10/2024    09:00 - 16:00
Résumé :
Ces journées s'inscrivent dans le cadre de l'axe 3 (Physique mathématique, Physique Statistique, Combinatoire) de la fédération de recherche Math-STIC de l'Université Sorbonne Paris Nord, qui associe les laboratoires de mathématiques (LAGA), d'informatique (LIPN) et de traitement et transmission de l'information (L2TI). Les exposés auront lieu dans l'amphi Euler de l'Institut Galilée. Des repas (buffets) seront proposés le midi. L'inscription est gratuite mais obligatoire (avant le 20 septembre) pour faciliter l'organisation. Vendredi 4/10 Michael Drmota : The method of moments revisited with applications to planar maps The classical method of moments is used to prove limiting distributions by showing that properly centralized and/or scaled moments of a random variable converge to the corresponding moments of the limit. However, it is not always easy to obtain precise asymptotics for centralized moments - for example for proving a central limit theorem - due to "heavy cancellations". The main goal of this talk is to show some applications to random planar maps of a method of moments by Gao and Wormald that proves a central limit theorem without centralized moments. This is joint work with Eva-Maria Hainzl and Nick Wormald. Alice Contat : Parking on Cayley trees & Frozen Erdös-Rényi Consider a uniform rooted Cayley tree T_n with n vertices and let m cars arrive sequentially, independently, and uniformly on its vertices. Each car tries to park on its arrival node, and if the spot is already occupied, it drives towards the root of the tree and parks as soon as possible. Using combinatorial enumeration, Lackner & Panholzer established a phase transition for this process when m is approximately n/2 . We couple this model with a variation of the classical Erdös-Rényi random graph process. This enables us to describe completely the phase transition for the size of the components of parked cars using a modification of the standard multiplicative coalescent which we named the frozen multiplicative coalescent. The talk is based on joint work with Nicolas Curien. Andrew Elvey Price : Classification of D-finite walks in the quarter plane via elliptic functions Given a set of small steps, we consider the three variable generating function counting walks in the quarter plane using these steps. Since the seminal paper by Bousquet-Mélou and Mishna, the problem of characterising the generating function into the hierarchy Algebraic < D-finite < D-algebraic has received a lot of attention. For unweighted walks this characterisation is complete, however the existing proof of D-finiteness does not generalise to unweighted walks. In this talk I will describe our new proof that the generating function is D-finite in each variable if and only if the group of the walk is finite. This result applies to any weighted model is based on the elliptic function method. This is joint work with Thomas Dreyfus and Kilian Raschel. Enrica Duchi : TBA Quentin Berger : FK-percolation and Recursions on Galton-Watson Trees Some statistical mechanics models on trees may sometimes reduce to the study of some "simple" tree recursion; this is for instance the case for the FK-percolation model. It turns out that when the recursion is concave, we can compare this tree recursion to the one verified by (possibly non-linear) resistive networks. I will present a recent work with Irene Ayuso Ventura (Créteil), in which we obtain precise estimates on the asymptotic behaviour of non-linear conductances of Galton-Watson tree, also deriving some information on the FK-percolation model on random trees.
CALIN 03/10/2024 Journées MathStic Probabilités-Combinatoire 1, par Mireille Bousquet-Mélou, Mingkun Liu, Armand Riera, Meltem Ünel, Baptiste Louf
Mireille Bousquet-Mélou, Mingkun Liu, Armand Riera, Meltem Ãœnel, Baptiste Louf, Divers  
Amphithéâtre Euler, Institut Galilée
03/10/2024    09:30 - 17:30
Résumé :
Ces journées s'inscrivent dans le cadre de l'axe 3 (Physique mathématique, Physique Statistique, Combinatoire) de la fédération de recherche Math-STIC de l'Université Sorbonne Paris Nord, qui associe les laboratoires de mathématiques (LAGA), d'informatique (LIPN) et de traitement et transmission de l'information (L2TI). Les exposés auront lieu dans l'amphi Euler de l'Institut Galilée. Des repas (buffets) seront proposés le midi. L'inscription est gratuite mais obligatoire (avant le 20 septembre) pour faciliter l'organisation. Jeudi 3/10 Mireille Bousquet-Mélou : Combinatorics of 3-coloured quadrangulations This talk deals with the enumeration of (planar) maps equipped with a proper 3-colouring of their vertices. The case of triangulations is well-understood, with an algebraic generating function and bijective solutions. The case of general planar maps is still algebraic, but the combinatorial explanations for that are missing. We will focus on quadrangulations, for which algebraicity is lost. We will see that this problem admits several interesting reformulations (in terms of orientations, of height functions...), which suggest to record in the enumeration other statistics, beyond the edge number. We will present solutions for some bivariate problems, obtained in collaboration with Andrew Elvey Price (Tours). Mingkun Liu : Length spectra of random metric maps: a Teichmüller theory approach In this talk, I will first discuss short closed geodesics on a random hyperbolic surface of large genus, and we will see that the lengths of these geodesics are distributed in exactly the same way as those of the short cycles in a big random map (following the work of Mirzakhani­­-Petri and Janson-Louf). Next, I will present a joint work with Simon Barazer and Alessandro Giacchetto, where we study random maps of large genus with a Teichmüller theory approach. Armand Riera : TBA Meltem Ünel : TBA Baptiste Louf : Counting with random walks We are interested in an enumerative problem, namely counting geometric objects called combinatorial maps, which can be parametrized by two numbers: their size, and a topological parameter called the genus. We are interested in an asymptotic estimation of the number of these objects when both the size and the genus go to infinity. While enumeration in one parameter is a very well studied topic with many powerful tools available, this problem is a case of bivariate enumeration, is a rather new topic with very few results known at the moment. Our method consists in studying a recurrence formula for these maps and modeling it by a random walk, forgetting completely about the combinatorics of the model. This is a work in progress with Andrew Elvey-Price, Wenjie Fang and Michael Wallner.
CALIN 01/10/2024 Heavy-tailed covariates in high dimensions, par Gabriele Sicuro
Gabriele Sicuro, Alma Mater — Università di Bologna  
Salle B107, bâtiment B, Université de Villetaneuse
01/10/2024    14:00 - 15:00
Résumé :
Machine learning theoretical models very often assume a dataset obtained from a Gaussian distribution, or from a Gaussian mixture. The possible limitations of such a Gaussian assumption have been recently object of investigation, and theoretically characterization, leading to a number of "Gaussian universality" results. In this talk I will present an analytical treatment of the performance in high dimensions of simple architectures on heavy-tailed distributed datasets, showing that even simple generalized linear models exhibit a striking dependence on non-Gaussian features in both classification and regression tasks.
LOVE 26/09/2024 Linear approximation of the ?-calculus: a new presentation of an old thing, par Remy Cerda
Remy Cerda, IRIF/I2M  
Salle B107, bâtiment B, Université de Villetaneuse
26/09/2024    10:30 - 16:00
Résumé :
The Taylor expansion of ?-terms, introduced by Ehrhard and Regnier in the early 2000s, is now a celebrated tool that allows for a theory of (multi)linear approximation for various ?-calculi, refining the traditional approach based on partial orders and (Scott-)continuity. However, both the continuous approximation theorem and its linear counterpart (known as the Commutation theorem) speak “only” about ?-normalisation. I will explain how moving the focus to ?-reduction is made possible by considering infinitary extensions of the ?-calculus, thanks to a simulation theorem unifying several standard results. If time permits, I will also show how this suggests a lazy Taylor expansion, as well as a limitation to further straightforward extensions. The work presented is joint with Lionel Vaux Auclair. It corresponds to the main story of my PhD thesis.
AOC 12/09/2024 A Knowledge Compilation Take on Binary Boolean Optimization, par Florent Capelli
Florent Capelli, CRIL  
Salle C308, Institut Galilée, Université de Villetaneuse
12/09/2024    11:00 - 12:00
Résumé :
The Binary Boolean Optimization (BPO) problem aims at finding the maximal value that a rational polynomial P(x) can take when x is supposed to be a vector with 0 and 1 values. This non-linear optimization problem has recently received renewed attention. Current techniques for solving it either involve to solve a linear relaxation of the problem or use dedicated algorithm exploiting some structure in the way monomials are interacting with one another, allowing one to skip large parts of the search space compared to the brute force approach. In this talk, we present and explore the consequences of an interesting connection between BPO instances and another well studied problem on Boolean functions: the Algebraic Model Counting (AMC) problem. Given a Boolean function f on variables X and a weight on each of its variable, the AMC problem aims at finding the sum of the weights of every satisfying assignments of f. This problem can encode a lot of different tasks by simply changing the underlying algebraic structure where the sum and products are made. This way, we show how one can reformulate BPO instances as an AMC problem on an algebraic structure known as the (max,+)-semiring. The consequences of this connection are manyfold. In particular, we are able to recover every known results on the tractablability of BPO problem from this connection and the existing literature on the complexity of AMC. More importantly, this connection allows us to discover new tractable classes for BPO and is flexible enough so that we can find tractable instances of the slight variations of BPO such as BPO with cardinality constraints or pseudo-Boolean BPO, two problems for which few tractability results where known. More importantly, this approach yields practical results: by running a modified version of d4, a tool originally made for knowledge compilation, so that it performs AMC on the (max,+)-semiring instead, we show that our approach is competitive with the existing ones on hard instances. This talk will cover a gentle presentation of the BPO problem and its connection with AMC. We will then give a quick overview on existing techniques for solving AMC that are based on Knowledge Compilation and how this approach is fruitful for solving extensions of the BPO problem. We will conclude by a presentation of the way d4 works and of our practical results.
LOVE 12/09/2024 Characterisations of polynomial-time and -space complexity classes over the reals, par Manon Blanc
Manon Blanc, LiX  
Salle B107, bâtiment B, Université de Villetaneuse
12/09/2024    10:30 - 12:00
Résumé :
Many recent works have studied how analogue models work, compared to classical digital ones. By “analogue” models of computation, we mean computing over continuous quantities, while “digital” models work on discrete structures, like bits. It led to a broader use of Ordinary Differential Equation (ODE) in computability theory. From this point of view, the field of implicit complexity has also been widely studied and developed. We show here, using arguments from computable analysis, that we can algebraically characterise PTIME and PSPACE for functions over the reals. We will use at first using discrete ODEs and more precisely the so-called Linear Length ODEs schemata, and then we will show we can use continuous ODEs.
CALIN 11/09/2024 The magic number pi: computation and proof of irrationality, par Michael Drmota
Michael Drmota, Institute of Discrete Mathematics and Geometry  
Salle B107, bâtiment B, Université de Villetaneuse
11/09/2024    15:00 - 15:00
Résumé :
talk for the students, EUR Math&CS
CALIN 10/09/2024 Quelques progrès récents sur les fonctions G et les fonctions E, par Javier Fresán
Javier Fresán, Institut de Mathématiques de Jussieu-Paris Rive Gauche, Sorbonne Université  
Salle B107, bâtiment B, Université de Villetaneuse
10/09/2024    14:00 - 15:30
Résumé :
Les fonctions G et les fonctions E sont des séries entières à coefficients algébriques qui sont solution d'une équation différentielle et satisfont à des conditions de croissance de nature arithmétique. Elles correspondent aux fonctions holonomes/D-finies qui apparaissent dans de nombreux problèmes en combinatoire, probabilité, physique. Elles ont été introduites dans le mémoire de Siegel sur les applications de l'approximation diophantienne en 1929, dans le but de généraliser les résultats de transcendence pour les valeurs de la fonction exponentielle en des arguments algébriques. Je survolerai de façon accessible quelques progrès récents, voire très récents, et moins récents sur les fonctions G et les fonctions E, en mettant l'accent sur deux questions : quelle est la structure de leurs équations différentielles ? quelle place occupent les fonctions hypergéométriques parmi elles ?
LOVE 05/09/2024 The Fundamental Theorem of Calculus for the Lebesgue Integral in Coq and its applications, par Reynald Affeldt
Reynald Affeldt , AIST (National Institute of Advanced Industrial Science and Technology).  
Salle B107, bâtiment B, Université de Villetaneuse
05/09/2024    10:30 - 11:30
Résumé :
The MathComp-Analysis team has been formalizing analysis on top of the Mathematical Components library, the Coq library behind the celebrated formalizations of the Four color theorem and of the Feit-Thompson theorem. In this talk, we explain an original formalization of the Fundamental Theorem of Calculus (FTC) for the Lebesgue Integral using MathComp-Analysis. We believe that it illustrates a desirable approach to formalized mathematics: an incremental and collaborative development of loosely-coupled theories that culminates with a central lemma (here, the Lebesgue Differentiation Theorem) from which results of interest are easily derived (among them: the FTC). This work relates at last differentiation and integration in MathComp-Analysis and incidentally lends itself to a direct application to probabilistic programming. We use it to formalize the Beta probability distribution and complete the formalization of Shan's proof by equational reasoning of Eddy's table game. -- Théorème fondamental de l'analyse pour l'intégrale de Lebesgue dans Coq et ses applications Les contributeurs de MathComp-Analysis formalisent des éléments d'analyse à partir de la librairie Mathematical Components, la librairie Coq qui supportent les formalisations du théorème des quatre couleurs et du théorème de Feit-Thompson. Nous proposons dans ce contexte une formalisation originale du théorème fondamental de l'analyse pour l'intégrale de Lebesgue. Nous pensons qu'elle illustre une approche souhaitable pour formaliser les mathématiques : un développement incrémental et collaboratif de théories faiblement couplées qui culmine avec un lemme central (ici, le théorème de différentiation de Lebesgue) à partir duquel des résultats importants peuvent être facilement dérivés (parmi eux : le théorème fondamental de l'analyse). Ce résultat relie enfin la dérivation et l'intégration dans MathComp-Analysis et trouve par exemple une application à la programmation probabiliste. Nous l'utilisons pour formaliser la distribution de probabilité Beta et compléter ainsi la formalisation de la preuve par raisonnement équationnel du jeu de table d'Eddy par Shan.
AOC 20/06/2024 Partial optimality in linear ordering, par David Stein
David Stein, TU Dresden  
Salle A303, Université de Villetaneuse
20/06/2024    10:30 - 11:30
Résumé :
The linear ordering problem consists in finding a linear order < on a finite set A so as to minimize the sum of costs associated with pairs of elements a,b for which a < b. The problem is NP-hard and APX-hard. We introduce algorithms for solving the problem *partially* by deciding efficiently for some pairs (a,b) whether a
LOVE 03/06/2024 CosyVerif: The Path to Formalisms Cohabitation, par Van-François LE
Van-François LE, Université Sorbonne Paris Nord  
Salle A303, bâtiment A, Université de Villetaneuse
03/06/2024    11:45 - 12:45
Résumé :
More and more model checking approaches rely nowadays on several inputs, potentially expressed in different formalisms. Tools implementing these usually include only the expected formalisms. Thus, such tools are ad-hoc and lack extensibility and interoperability features, especially when new formalisms are needed. The challenge is then to design a generic and easy way for several formalisms to cohabit in such verification software. Creation, exchange, and interoperability between formalisms would be facilitated, thus saving numerous development efforts. The originality of the CosyVerif platform lies in its capability to easily and rapidly gather diverse formalisms within a same framework, and to provide extension facilities to integrate new ones.
CALIN 28/05/2024 Lattice paths and branched continued fractions: Coefficientwise Hankel total positivity of the Laguerre polynomials, par Bishal Deb
Bishal Deb, Laboratoire de Probabilités, Statistique et Modélisation (LPSM), Sorbonne Université and Université Paris Cité, CNRS, Paris  
Salle B107, bâtiment B, Université de Villetaneuse
28/05/2024    14:00 - 15:00
Résumé :
The Laguerre polynomials are a family of orthogonal polynomials which have been well-studied in combinatorics. The coefficients of these polynomials enumerate a certain family of graphs which have been called Laguerre digraphs or Laguerre configurations. The polynomial sequence has a well-known Stieltjes moment representation, i.e., these polynomials can be expressed as the sequence of moments of a certain measure supported on the positive real-axis. It is known that a sequence is a Stieltjes moment sequence if and only if its Hankel matrix is totally positive. A natural question is to ask if the Hankel matrix is also coefficientwise totally positive. We will address this question in this talk. We will begin by stating the main theorem which will not require any prerequisites. We then motivate this result; we first state the equivalence between Stieltjes moment sequences and the total positivity of Hankel matrices, then we mention how this theory has been extended coefficientwise. We introduce the production-matrix method which is a powerful tool to prove total positivity. Finally, we sketch a proof of our main theorem.
LOVE 22/05/2024 Languages of Higher Dimensional Timed Automata, par Emily Clement
Emily Clement, IRIF, Université Paris Cité  
Salle B107, bâtiment B, Université de Villetaneuse
22/05/2024    14:00 - 15:00
Résumé :
Higher Dimensional Automata (HDA) are a very powerful tool to represent non-interleaving concurrency (i.e. a || b =/= a.b + b.a). They generalise numerous models, such as Timed Automata. Languages of HDA are sets of ipomsets, which represent the possible order on the events. In recent years, interest in HDAs has increased and has led to numerous new results (e.g. 2021 Fahrenberg et al., 2023: Fahrenberg et al.). Recently, an extension of both Timed Automata and HDA were defined, called Higher Dimensional Timed Automata, to obtain a more refined information on posets: rather than only the precedence order, we are interested in the time intervals in which events are active In our work, we define languages of HDTAs as sets of interval-timed pomsets with interfaces. As an application, we show that language inclusion of HDTAs is undecidable. On the other hand, using a region construction, we can show that untimings of HDTA languages have enough regularity so that untimed language inclusion is decidable.
CALIN 21/05/2024 Mini course on popular matchings, lecture 3, par Prof. Kavitha Telikepalli
Prof. Kavitha Telikepalli, Dean of School of Technology and Computer Science, TIFR, India  
Salle B107, bâtiment B, Université de Villetaneuse
21/05/2024    14:00 - 15:45
Document attaché
Résumé :
Lecture 3: Popular assignments and extensions. This talk will be on popular matchings in the one-sided preferences model. Popular matchings need not always exist in this model and there is a simple combinatorial algorithm to decide if one exists. We will see an LP-duality inspired algorithm for the more general problem of deciding if a popular assignment (i.e., a popular maximum-matching) exists or not. This algorithm can be generalized to solve the popular common base problem in the intersection of two matroids where one matroid is the partition matroid, this implies the popular arborescence problem (relevant in liquid democracy) can be solved efficiently. This mini-course is supported by the École Universitaire de Recherche de Paris Nord en Mathématiques et Informatique; https://eur.univ-paris13.fr/events/popular-matchings-mini-course-by-kavitha-telikepalli-tata-institute/.
CALIN 14/05/2024 Mini course on popular matchings, lecture 2, par Prof. Kavitha Telikepalli
Prof. Kavitha Telikepalli, Dean of School of Technology and Computer Science, TIFR, India  
Salle B107, bâtiment B, Université de Villetaneuse
14/05/2024    14:00 - 15:45
Document attaché
Résumé :
Lecture 2: Popular matchings and optimality. In this talk we will consider algorithms for finding optimal popular matchings. While it is easy to find max-size popular matchings, it is NP-hard to find a min-cost popular matching. This motivates us to relax popularity to a weaker notion called "quasi-popularity". Describing the popular and quasi-popular matching polytopes is hard, but there is an easy-to-describe integral polytope sandwiched between these two hard ones. So we can efficiently find a quasi-popular matching of cost at most that of a min-cost popular matching. This mini-course is supported by the École Universitaire de Recherche de Paris Nord en Mathématiques et Informatique; https://eur.univ-paris13.fr/events/popular-matchings-mini-course-by-kavitha-telikepalli-tata-institute/.
CALIN 07/05/2024 Mini course on popular matchings, lecture 1, par Prof. Kavitha Telikepalli
Prof. Kavitha Telikepalli, Dean of School of Technology and Computer Science, TIFR, India  
Salle B107, bâtiment B, Université de Villetaneuse
07/05/2024    16:00 - 17:45
Document attaché
Résumé :
Lecture 1, Introduction to popular matchings. The problem of computing a stable matching in a bipartite graph is an old and well-studied problem. Gale and Shapley showed in 1962 that such a matching always exists and can be efficiently computed. This is a classical result in algorithms with many applications in economics and computer science. Stability is a strong and rather restrictive notion. This series of talks will be on a relaxation of stability called "popularity". In the first talk we will see simple and efficient algorithms for some popular matching problems. No background in algorithms or matching theory will be assumed. This mini-course is supported by the École Universitaire de Recherche de Paris Nord en Mathématiques et Informatique; https://eur.univ-paris13.fr/events/popular-matchings-mini-course-by-kavitha-telikepalli-tata-institute/.
CALIN 07/05/2024 Topology of the arc complex, par Pallavi Panda
Pallavi Panda , LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
07/05/2024    14:00 - 15:30
Résumé :
The arc complex is a pure flag simplicial complex associated to a finite-type topological surface with marked points. It was discovered by Harvey and used by geometers like Harer, Penner, Bowditch, Epstein to study geometric properties of hyperbolic surfaces, their Teichmüller spaces and their mapping class groups. The arc complex is also a subcomplex of the cluster complex of a cluster algebra, defined by Fomin-Zelevinksy. For most of the surfaces, the arc complex is locally non-compact. In this talk, I will discuss about the simplicial topology of the arc complex in the finite cases. In particular, I will focus on the shellability (analogous to simply-connectedness) and collapsibility (analogous to contractibility) of these finite complexes and prove that they are closed combinatorial balls. Related articles: https://arxiv.org/abs/2402.10530, https://arxiv.org/abs/2306.06695
CALIN 30/04/2024 Les bijoux de la tessellation idéale de Poisson-Voronoï de l'espace hyperbolique, par Matteo D'Achille
Matteo D'Achille, Laboratoire de Mathématiques d'Orsay  
Salle B107, bâtiment B, Université de Villetaneuse
30/04/2024    14:00 - 15:00
Résumé :
Nous discuterons de la limite de faible intensité des tessellations de Poisson--Voronoï sur les espaces hyperboliques, alias tessellations idéales de Poisson--Voronoï (IPVT de l'anglais). En particulier, nous verrons comment une simple description poissonnienne de la cellule qui contient l'origine de l'espace hyperbolique (cellule zéro) permet d'étudier des propriétés fines des tuiles de l'IPVT. L'exposé présentera des impressions en 3D de réalisations de la cellule zéro de l'IPVT de l'espace hyperbolique tridimensionnel dans le modèle de la boule de Poincaré. Travail en collaboration avec Nicolas Curien, Nathanaël Enriquez, Russell Lyons et Meltem Ünel. Pour en savoir plus sur les bijoux : https://matteodachille.github.io/ipvt
LOVE 25/04/2024 Typing Nets as a cost-effective Presentation of the Curry-Howard Isomorphism, par Paulin Jacobé de Naurois
Paulin Jacobé de Naurois, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
25/04/2024    10:30 - 11:30
Résumé :
We provide a cost-effective presentation of the Curry-Howard Isomorphism for Linear Logic: Using an extension of lambda-calculus with explicit substitutions, a presentation of type derivations as an extension of Linear Logic Proof Nets, and succinct representations for describing our objects, we establish a tight complexity correspondence between cut-elimination in Linear Logic and beta-reduction in lambda-calculus. This tight correspondence scales to time and space complexity, as well as sequential and parallel computations.
LOVE 11/04/2024 Introduction à la sémantique fonctorielle des théories algébriques généralisées, par Jonas Frey
Jonas Frey, CMU  
Salle B107, bâtiment B, Université de Villetaneuse
11/04/2024    10:30 - 12:00
Résumé :
Cet exposé présentera des travaux récents [1] sur une théorie de dualité pour les *clans*, qui sont représentations catégorielles des *théories algébriques généralisées* de Cartmell (generalized algebraic theories, GATs). Les GATs appartiennent à la méta-théorie de la théorie des types puisque les représentations algébriques des théories des types telles que les « catégories avec familles » peuvent elles-mêmes être décrites par les GATs. En fonction du temps et de l'intérêt, je conclurai en discutant des idées sur les raffinements linéaires des GATs [2]. [1] https://arxiv.org/abs/2308.11967 [2] https://github.com/jonas-frey/pdfs/blob/master/cost-wg6-2024-slides.pdf
AOC 28/03/2024 Heuristic and Exact Algorithms for Solving the Electric Autonomous Dial-A-Ride Problem, par Yue Su
Yue Su, Enpc  
Salle B107, bâtiment B, Université de Villetaneuse
28/03/2024    10:30 - 11:30
Résumé :
We propose highly efficient heuristic and exact algorithms to solve the Electric Autonomous Dial-A-Ride Problem (E-ADARP), which consists in designing a set of minimum-cost routes that accommodates all customer requests for a fleet of Electric Autonomous Vehicles (EAVs). The E-ADARP has two important features: (i) the employment of EAVs and a partial recharging policy; (ii) the weighted-sum objective function that minimizes the total travel time and the total excess user ride time. We first propose a Deterministic Annealing (DA) algorithm to solve the E-ADARP. Partial recharging (i) is handled by an exact route evaluation scheme of linear time complexity. To tackle (ii), we propose a new method that allows effective computations of minimum excess user ride time by introducing a fragment-based representation of paths. To validate the performance of the DA algorithm, we compare our algorithm results to the best-reported Branch-and-Cut (B&C) algorithm results on existing instances. Our DA algorithm provides 25 new best solutions and 45 equal solutions for 84 existing instances. To test the algorithm's performance on larger-sized instances, we establish new instances with up to 8 vehicles and 96 requests, and we provide 19 new solutions for these instances. Then, we present a highly efficient CG algorithm, which is integrated into the Branch-and-price (B&P) scheme to solve the E-ADARP exactly. Our CG algorithm relies on an effective labeling algorithm to generate columns with negative reduced costs. In the extension of labels, the key challenge is determining all excess-user-ride-time optimal schedules to ensure finding the minimum-negative-reduced-cost route. To handle this issue, we apply the fragment-based representation and propose a novel approach to abstract fragments to arcs while ensuring excess-user-ride-time optimality. We then construct a new graph that preserves all feasible routes of the original graph by enumerating all feasible fragments, abstracting them to arcs, and connecting them with each other, depots, and recharging stations in a feasible way. On the new graph, we apply strong dominance rules and constant-time feasibility checks to compute the shortest paths efficiently. In the computational experiments, we solve 71 out of 84 instances optimally, improve 30 previously reported lower bounds, and generate 41 new best solutions on previously solved and unsolved instances.
AOC 27/03/2024 Optimisation de la réserve de charge dans un réseau électrique, par Dimitri Watel
Dimitri Watel  
Salle B107, bâtiment B, Université de Villetaneuse
27/03/2024    10:00 - 11:00
Résumé :
Dans un réseau électrique, le flot électrique n'est pas choisi librement pas l'opérateur. Il découle des appels de puissance effectués par les consommateurs et du graphe du réseau. Connaissant ces deux paramètres, on peut déduire la valeur du flot dans chaque câble du réseau. L'opérateur peut jouer sur le réseau avec deux paramètres : en désactivant un ou plusieurs nœuds ou en forçant l'orientation du courant électrique. Une fois ces actions choisies, l'opérateur peut estimer la valeur du flot dans tout le réseau. L'objectif de ce dernier est d'éviter une surcharge des sources électriques, ce qui pourrait provoquer son arrêt et donc une surcharge d'autres sources. Avec cet effet boule-de-neige, l'opérateur cours le risque d'un black-out total. Une possibilité pour éviter ce phénomène est d'optimiser la réserve de charge. La charge d'une source est le pourcentage d'utilisation de sa capacité de production, qui doit rester loin de 100% pour éviter une surcharge. La réserve de charge est la différence entre la charge maximum et la charge minimum de l'ensemble des sources. Ainsi, un réseau équilibré est un réseau où toutes les sources sont utilisées avec le même pourcentage. Ce type d'optimisation garanti aussi un revenu équitable quand les acteurs produisant de l'énergie n'ont pas tous la même capacité de production. Notre problème se décrit donc ainsi : connaissant un réseau électrique et les appels de charge des consommateurs, quelles sont les actions de désactivation et d'orientation que l'opérateur doit effectuer pour minimiser la réserve de charge. Nous nous intéressons dans ce problème à la complexité et l'approximabilité de ce problème. Nous montrons que ce problème est NP-Difficile et inapproximable dans le cas général. Il reste NP-Difficile même dans le cas où le réseau électrique est un arbre ; mais, dans ce cas, il existe un schémas d'approximation avec un rapport d'approximation absolu. La fin de la présentation abordera la difficulté de la production d'instances réalistes et l'évaluation de ces algorithmes.
LOVE 21/03/2024 n algebraic approach for union bound reasoning about probabilistic programs, par Leandro Gomes
Leandro Gomes, Univ. Lille  
Salle B107, bâtiment B, Université de Villetaneuse
21/03/2024    10:30 - 12:00
Résumé :
Kleene Algebra with Tests (KAT) provides a framework for algebraic equational reasoning on imperative programs. The recent variant Guarded KAT (GKAT) allows to reason on non-probabilistic properties of probabilistic programs. Here we introduce an extension of this framework called aGKAT (approximate GKAT), a form of graded GKAT over a partially ordered monoid (real numbers) which enables to express satisfaction of (deterministic) properties except with a probability up to a certain bound. This allows to represent in equational reasoning ’à la KAT’ proofs of probabilistic programs based on the union bound, a technique from basic probability theory. We show how a propositional variant of approximate Hoare Logic (aHL), a program logic for union bound, can be soundly encoded in our system aGKAT. We then illustrate the use of aGKAT on an example of accuracy analysis from the field of differential privacy.
AOC 21/03/2024 Optimal Planning and Pricing of Electric Vehicle Charging Services, par Miguel Anjos
Miguel Anjos, University of Edinburgh  
Salle B107, bâtiment B, Université de Villetaneuse
21/03/2024    10:30 - 11:30
Résumé :
The increase of electric vehicle (EV) adoption in recent years has correspondingly increased the importance of providing adequate public charging services for EV users. For a charging service provider, a key question is to determine the optimal location and sizing of charging stations, as well as the price for charging, with respect to a given objective and subject to budget and other practical constraints. Practical objectives include maximizing EV adoption as part of a public policy on electric transportation, and maximizing the profit gained from providing this service. I will present an overview of work to which I have contributed in this area, and discuss directions for ongoing and future research
LOVE 20/03/2024 Catégories différentielles et tangentes pour les algèbres sur une opérade, par Sacha Ikonicoff
Sacha Ikonicoff , University of Ottawa  
BBB Séminaires : https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 code : 757416
20/03/2024    17:00 - 18:00
Résumé :
La notion de catégorie différentielle cartésienne permet de formaliser dans un contexte catégorique la notion de dérivée directionnelle. Similairement, la notion de catégorie tangente fournit un analogue à la notion de fibré tangent de la géométrie différentielle dans le contexte de la théorie des catégories. Dans cet exposé, nous décrirons une nouvelle notion de monade différentielle cartésienne. Cette structure consiste en une monade équipée d'une transformation naturelle appelée "combinateur différentiel". Pour une telle monade, nous montrerons que la catégorie (opposée) de Kleisli associée est munie d'une structure différentielle cartésienne, et que la catégorie d'algèbres associée est munie d'une structure tangente. Finalement, nous considérerons l'exemple des algèbres sur une opérade. Nous montrerons que la monade associée à toute opérade (algébrique, symétrique) admet un combinateur différentiel. Nous étudierons la catégorie différentielle cartésienne et la catégorie tangente associée. Nous montrerons que cette catégorie tangente admet une structure tangente adjointe qui permet de retrouver certaines notions provenant de la géométrie algébrique et non-commutative.
LOVE 20/03/2024 Coherence semantics for pomset logic and a Self-Dual Modality for Non-Commutative Contraction and Duplication , par Christian Retoré
Christian Retoré, LIRMM Univ Montpellier  
Salle B107, bâtiment B, Université de Villetaneuse
20/03/2024    10:30 - 11:30
Résumé :
We shall first present pomset logic, a non commutative extension of classical linear logic with a self dual non commutative connective < as a proof net calculus issued from coherence semantics: proofnets correctness is equivalent to semantical correctness. Next we semantically define a modality "flag" in the category of coherence spaces with two inverse linear (iso)morphisms: 1) "duplication" from (flag C) to ((flag C) < (flag C)) 2) "contraction" from ((flag C) < (flag C)) to (flag C) and a pair of morphisms between C and (flag C) making C a retract of (flag C) A token in the web of (flag C) is a continuous functions from 2^omega to the web of C (discrete topology on 2, product topology on 2^omega, discrete topology on the web of C). We shall conclude by wondering about a possible syntax for the modality flag.
RCLN 18/03/2024 MAFALDA : Une étude comparative et complète de la détection et de la classification des sophismes, par Pierre Henri Paris
Pierre Henri Paris, Télécom Paris - IPP  
Salle B107, bâtiment B, Université de Villetaneuse
18/03/2024    12:15 - 13:15
Résumé :
Nous présentons MAFALDA, un benchmark pour la classification des sophismes qui fusionne et unifie les ensembles de données antérieurs sur les sophismes. Il s'accompagne d'une taxonomie qui aligne, affine et unifie les classifications existantes des sophismes. Nous fournissons également une annotation manuelle d'une partie des données ainsi que des explications manuelles pour chaque annotation. Nous proposons un nouveau schéma d'annotation adapté aux tâches subjectives en NLP, ainsi qu'une nouvelle méthode d'évaluation conçue pour gérer la subjectivité. Nous évaluons ensuite plusieurs modèles de langage dans un contexte d'apprentissage zero-shot et les performances humaines sur MAFALDA afin d'évaluer leur capacité à détecter et à classer les sophismes.
AOC 14/03/2024 Covering some vertices with paths and a Hamiltonian degree condition for tough graphs, par Cléophée Robin
Cléophée Robin , Université de Caen  
Salle B107, bâtiment B, Université de Villetaneuse
14/03/2024    10:30 - 11:30
Résumé :
A graph G is Hamiltonian if it exists a cycle in G containing all vertices of G exactly once. A graph G is t-tough if, for all subsets of vertices S, the number of connected components in G ? S is at most |S| / t. In 1973, Chvàtal conjecture the following : There exists a constant t such that every t-tough graphs is Hamiltonian. Let t be a positive integer. A graph G with degree sequence d_1,d_2,...,d_n is P(t) (t being a positive integer) If for all i, t ? i
LOVE 13/03/2024 Model-based High-level Integration of Heterogeneous Components for co-simulation , par Jawher Jerray
Jawher Jerray , Telecom Paris  
Salle B107, bâtiment B, Université de Villetaneuse
13/03/2024    12:30 - 13:30
Résumé :
Because of their complexity, embedded systems are designed with sub-systems or components taken in charge by different development teams or entities and with different modeling frameworks and simulation tools, depending on the characteristics of each component. Unfortunately, this diversity of tools and semantics makes the integration of these heterogeneous components difficult. Thus, to evaluate their integration before their hardware or software is available, one solution would be to merge them into a common modeling framework. Yet, such a holistic environment supporting many computation and computation semantics seems hard to settle. Another solution we investigate is to generically link their respective simulation environments in order to keep the strength and semantics of each component environment. We present a method to simulate heterogeneous components of embedded systems in real-time. These components can be described at any abstraction level. Our main contribution is a generic glue that can analyze in real-time the state of different simulation environments and accordingly enforce the correct communication semantics between components.
LOVE 07/03/2024 Composable Partial Multiparty Session Types , par Claude Stolze
Claude Stolze  
Salle B107, bâtiment B, Université de Villetaneuse
07/03/2024    10:30 - 12:00
Résumé :
We introduce partial sessions and partial (multiparty) session types, in order to deal with open systems, i.e., systems with missing components. Partial sessions can be composed, and the type of the resulting system is derived from those of its components without knowing any suitable global type nor the types of missing parts. We apply these types to a process calculus, for which we prove subject reduction and progress, so that well-typed systems never violate the prescribed constraints. Therefore, partial session types support the development of systems by incremental assembling of components.
LOVE 06/03/2024 Controller for opacity problems on timed automata , par Laetitia Laversa
Laetitia Laversa, LIPN, Équipe LoVe  
Salle B107, bâtiment B, Université de Villetaneuse
06/03/2024    10:00 - 11:00
Résumé :
Timed automata are a common way of modelling real-time systems so that errors can be checked for or avoided. In particular, we may want to constrain the behaviour of the system so that it validates a safety property. We then seek to synthesise a controller that acts on the possible actions of the system at each moment of execution. On the other hand, we can represent a secret that we don't want to reveal by a private state in the timed automaton. The system is then opaque if, for every execution that passes through the private state, there is another execution with the same execution time that does not pass through the private time, and vice versa. In this talk, we will look at controller synthesis for the opacity problem.
LOVE 01/03/2024 Raisonnement sur les modèles de jeux dynamiques à l'aide de logiques d'obstruction., par Davide Catta
Davide Catta, Università degli studi di Napoli, DIETI, Italie  
Salle B107, bâtiment B, Université de Villetaneuse
01/03/2024    14:00 - 16:00
Résumé :
Les logiques d'obstruction sont des logiques temporelles que nous avons récemment introduites. Elles permettent de raisonner sur les propriétés temporelles des jeux dans lesquels un joueur peut modifier la structure topologique d'un graphe orienté en désactivant ses arcs. Dans ce séminaire, nous introduirons les propriétés formelles de ces logiques, en nous concentrant sur le problème du model checking. Nous montrerons également comment ces logiques permettent d'exprimer des propriétés de cybersécurité sur des graphes d'attaque.
LOVE 29/02/2024 Quasi-synchronous communications and verification of distributed systems, par Loïc Germerie Guizouarn
Loïc Germerie Guizouarn, Université Paris-Est Créteil (UPEC)  
Salle B107, bâtiment B, Université de Villetaneuse
29/02/2024    12:15 - 13:30
Résumé :
Distributed systems are typically based on asynchronous exchanges of messages. Communicating automata are a tool to reason formally on the communications of such systems, allowing to detect automatically errors, like deadlocks or loss of messages. Detecting these errors is undecidable in general for systems with two or more participants, and several restrictions of the model have been considered to restore decidability. The subject of this presentation is one of these approaches, based on systems whose executions are realisable with synchronous communications (RSC). The behaviour of these systems approximate synchronous behaviours, where messages are sent and received in an atomic action.
AOC 29/02/2024 Efficacité et équité dans le problème d'ordonnacement multi-organisation, par Martin Durand
Martin Durand, TU wien  
https://bbb.lipn.univ-paris13.fr/b/wol-ma9-vjn
29/02/2024    10:30 - 11:30
Résumé :
On considère le problème d'ordonnancement multi-organisation (POMO). Un ensemble de N organisations possèdent chacune un ensemble de machines et de tâches. Chacune de ses organisations dispose d'un ordonnancement, dit local, dans lequel elle ordonnance ses tâches sur ses machines. Notre but est de trouver un ordonnancement de toutes les tâches sur toutes les machines et tel que chaque organisation soit au moins aussi satisfaite dans cette solution globale qu'avec son ordonnancement local, cette contrainte est appelée contrainte de rationalité. On montre que la coopération peut permettre à toutes les organisations d'obtenir simultanément une meilleure solution. On étudie egalement à quel point la contrainte de rationalité impacte la qualité de la solution globale. Dans un second temps, on introduit un nouveau problème centré sur l'équité: on formule le bénéfice qu'une organisation obtient en coopérant et on étudie le problème de maximisation du plus petit bénéfice. On montre que ce problème est fortement NP-difficile et inapproximable dans le cas général et on propose une heuristique polynomiale qui retourne de bonnes solutions dans nos expérimentations.
LOVE 28/02/2024 Efficient Elimination and Reduction of Useless Mutants in Real-Time Model-based Systems, par James Ortiz
James Ortiz, Université de Namur  
Salle B107, bâtiment B, Université de Villetaneuse
28/02/2024    12:15 - 13:00
Résumé :
Mutation Testing (MT) is a test quality assessment technique that creates mutants by injecting artificial faults into the system and evaluating the ability of tests to distinguish these mutants. We focus on MT for safety-critical Timed Automata (TA). MT is prone to equivalent and duplicate mutants, the former having the same behavior as the original system and the latter other mutants. Such mutants bring no value to the testing process and induce useless test case executions, which can be long for timed systems. We present how the MUPPAAL mutation framework holistically addresses this problem. First, MUPPAAL integrates a non-refining mutant generation strategy eliminating all equivalent mutants. Second, MUPPAAL provides a novel operator that significantly reduces the number of duplicate mutants. Third, MUPPAAL supports the following strategies to effectively identify mutant duplicates: i) an exact bisimulation algorithm and ii) a simulation heuristic that exploits infected locations and transitions to generate discriminating traces. As a baseline, we additionally implemented a random simulation algorithm. We evaluated MUPPAAL on six real-time systems modeled in UPPAAL. Our results demonstrate that mutant duplicates can represent up to 32% of all the mutants and that our bisimulation algorithm can identify them more than 99% of the time. Our heuristic is ten times faster than bisimulation and limits the exploration to two times the number of exact duplicates compared to up to ten times for the baseline.
LOVE 13/02/2024 Reachability in Two-Parametric Timed Automata with One Parameter Is EXPSPACE-Complete, par Mathieu HILAIRE
Mathieu HILAIRE, LIRIS/Université Lyon 1  
Salle B107, bâtiment B, Université de Villetaneuse [BBB: https://bbb.lipn.univ-paris13.fr/b/ari-uht-t3u]
13/02/2024    10:00 - 11:00
Résumé :
Je présenterai les détails d'obtention des bornes inférieures et supérieures du problème, la borne supérieure étant basé sur une réduction aux automates à compteur paramétrique, tandis que la borne inférieure repose sur le principe de sérialisabilité.
RCLN 12/02/2024 Ethically-driven Multimodal Emotion Detection for Children with Autism, par Annanda Sousa
Annanda Sousa  
Salle B107, bâtiment B, Université de Villetaneuse
12/02/2024    12:15 - 13:15
Résumé :
Emotion detection (ED) aims to identify peopleÂ’s emotions automatically. However, most ED applications do not consider individuals who express emotions differently, such as people with autism. Although studies have already focused on creating ED models tailored for children with ASD, this application of ED suffers from a scarcity of resources and remains underperforming compared to the state-of-the-art ED models for the general population. This thesis addresses the gap in automatic ED between the general population and autistic children while ensuring an ethically driven approach, i.e., having the well-being of participants as the main priority during the whole research process. To meet our research objectives, we created a data collection framework that minimises emo- tional disruption to the participants, respects their privacy and rights according to GDPR, and provides a dataset that can be shared with the research community. We created CALMED, a multimodal annotated dataset for ED featuring children with autism that includes privacy- preserving features, novel target emotion classes, annotations provided by the participantsÂ’ par- ents and a researcher specialist who works with children with ASD. Using the CALMED dataset, we created hundreds of models with unique configurations and analysed them to explore the effectiveness of various methods for multimodal ED in autism. Then, utilising the knowledge acquired in this analysis, we proposed a multimodal ED model that outperformed the previous state-of-the-art, reaching 81.56% and 75.47% for accuracy and balanced accuracy, respectively. Finally, we created and shared many systems to support the data acquisition process and data experiments creation and analysis. We placed great importance on ensuring reproducibility, reusability, and ethical conduct. This research has made significant contributions to the field of ED applied to ASD. It has provided a valuable dataset, analytical insights, a state-of-the-art model, and many computer systems that can serve as a groundwork for future work.
RCLN 08/02/2024 The role of Knowledge Graphs in externalizing information from conceptual models, par Ana-Maria Ghiran
Ana-Maria Ghiran, UBB Cluj (Roumanie)  
Salle B107, bâtiment B, Université de Villetaneuse
08/02/2024    12:15 - 13:15
Résumé :
Due to the machine readable format used by Knowledge Graphs (KGs) in representing facts, and ontological models, they enabled AI systems to make decisions or to provide humans with insights by revealing hidden relationships between entities. Nevertheless, decision making in enterprises is far from being assigned to AI. Describing and evaluating business processes take the form of visual models that gained increased popularity among managers. But a business process diagram, usually described in the standardized notation BPMN (Business Process Model and Notation), enables more than just a visual representation of the knowledge – it creates a structured encoding of knowledge, which can be captured in a graph-based format. In this way, information that captures diverse facets of an enterprise (e.g. about business processes, resources, strategies, goals etc.) and that was mainly used by business executives and restricted to human interpretation, is externalized as KGs and provided for machine interpretation, thus enabling reasoning and semantic linking with external knowledge. In this presentation I will highlight that conceptual models should be considered as knowledge acquisition structures for any domain and that they can be processed as KGs with the help of Semantic Technology.
LOVE 08/02/2024 Intuitionistic continuous logic , par Jérémie Marquès
Jérémie Marquès, IRIF  
Salle B107, bâtiment B, Université de Villetaneuse
08/02/2024    10:30 - 11:30
Résumé :
Continuous logic is obtained by replacing the binary truth values by the reals between 0 and 1. I will explain how this logic arises topologically from usual logic by removing a zero-dimensionality assumption, thus making it very natural. Many results from the "binary" setting generalize. We will focus on intuitionistic logic, where Pitts' uniform interpolation theorem remains valid in the continuous setting.
AOC 08/02/2024 Exponentially large arc-flow models, par François Clautiaux
François Clautiaux, Université de Bordeaux, Laboratoire CNRS IMB  
Salle B107, bâtiment B, Université de Villetaneuse
08/02/2024    10:30 - 11:30
Résumé :
Network flow formulations are among the most successful tools to solve optimization problems. Such formulations correspond to determining an optimal flow in a network. One particular class of network flow formulations is the arc flow, where variables represent flows on individual arcs of the network. In this talk, we will review classical and recent results on integer linear programming models based on arc-flow formulations in exponentially or pseudo-polynomial size networks. We will study the limitations of these approaches, and how various almost disconnected groups have addressed these limitations. We will describe a recent approach based on the generalization of these models to flow in hypergraphs, and propose some research directions.
LOVE 07/02/2024 Efficient Convex Zone Merging in Parametric Timed Automata , par Dylan Marinho
Dylan Marinho, Télécom SudParis  
Salle B107, bâtiment B, Université de Villetaneuse
07/02/2024    12:30 - 13:30
Résumé :
Parametric timed automata are a powerful formalism for reasoning on concurrent real-time systems with unknown or uncertain timing constants. Reducing their state space is a significant way to reduce the inherently large analysis times. In this talk, I will present different merging reduction techniques based on convex union of constraints (parametric zones), allowing to decrease the number of states while preserving the correctness of verification and synthesis results. In the main paper, we perform extensive experiments, and identify the best heuristics in practice, bringing a significant decrease in the computation time on a benchmarks library. This talk is mainly based on a publication at FORMATS'22 and on join works with Étienne André, Laure Petrucci and Jaco van de Pol.
LOVE 01/02/2024 Higher-Order Bayesian Networks, Exactly, par Gabriele Vanoni
Gabriele Vanoni, IRIF  
Salle B107, bâtiment B, Université de Villetaneuse
01/02/2024    10:30 - 11:30
Résumé :
Bayesian networks are graphical first-order probabilistic models that allow for a compact representation of large probability distributions, and for efficient inference, both exact and approximate. We introduce a higher-order programming language, in the idealized form of a lambda-calculus, which we prove sound and complete w.r.t. Bayesian networks: each Bayesian network can be encoded as a term, and conversely each (possibly higher-order and recursive) program of ground type compiles into a Bayesian network. The language allows for the specification of recursive probability models and hierarchical structures. Moreover, we provide a compositional and cost-aware semantics which is based on factors, the standard mathematical tool used in Bayesian inference. Our results rely on advanced techniques rooted into linear logic, intersection types, rewriting theory, and Girard's geometry of interaction, which are here combined in a novel way. This is joint work with Claudia Faggian and Daniele Pautasso.
AOC 25/01/2024 A branch-and-bound method for multiobjective mixed integer quadratic programs based on dual relaxations, par Marianna De Santis
Marianna De Santis, Università di Roma  
Salle B107, bâtiment B, Université de Villetaneuse
25/01/2024    10:30 - 11:30
Résumé :
Most real-world optimization problems in the areas of applied sciences, engineering and economics involve multiple, often conflicting and nonlinear, goals. In the mathematical model of these problems, under the necessity of reflecting discrete quantities, logical relationships or decisions, integer and 0-1-variables need to be introduced, leading to MultiObjective Mixed Integer Nonlinear Programming problems (MO-MINLPs). The practical relevance of MO-MINLPs is pointed out in many publications, where tailored approaches for specific applications have been proposed. MO-MINLPs are intrinsically nonconvex, implying that the design of exact and efficient solution methods is particularly challenging and requires global optimization techniques. In this talk, we present a branch-and-bound method for multiobjective mixed-integer convex quadratic programs that computes a superset of efficient integer assignments and a coverage of the nondominated set. The method relies on outer approximations of the upper image set of continuous relaxations. These outer approximations are obtained addressing the dual formulations of specific subproblems where the values of certain integer variables are fixed. The devised pruning conditions and a tailored preprocessing phase allow a fast enumeration of the nodes. Despite the fact that we do not require any boundedness of the feasible set, we are able to prove that the method stops after having explored a finite number of nodes. Numerical experiments on instances with two, three, and four objectives are presente
LOVE 18/01/2024 De la cohérence aux quantales, et ensuite à la topologie dirigée, par Cameron Calk
Cameron Calk, LIS  
Salle B107, bâtiment B, Université de Villetaneuse
18/01/2024    10:30 - 11:30
Résumé :
Dans cet exposé, je présente deux travaux en cours reliant la théorie de la réécriture, l’algèbre non-commutative et la topologie (dirigée). Le premier tel lien provient d’un travail précédent dans lequel nous avons établi une formalisation de théorèmes de cohérence catégoriques dans le cadre des algèbres de Kleene de dimension supérieure. Dans un premier temps, je rappellerais rapidement ces structures et résultats. Ce lien étroit entre structures catégoriques et algèbres nous a conduit à une correspondance à la Jónsson-Tarski entre les catoïdes (supérieures), généralisant les catégories supérieures, et les quantales (supérieures). Ces derniers ont été introduit en tant que extension non-commutative des locales et sont aussi étudiés dans le cadre de la logique catégorique. La première partie de l’exposé concernera cette correspondance ainsi que ses liens avec les algèbres de convolution associées. Tous ces résultats ont été formalisés dans l’assistant de preuve Isabelle. Dans la deuxième partie de l'exposé je parlerais d’un travail en cours reliant la réécriture, les quantales et des méthodes topologiques (dirigées). Le but de ce travail est de caractériser les congruences des treillis multinomiaux et de leurs analogues continus, en particulier le quantale des endomorphismes sup-continus de l’intervalle ordonné. Ces premiers, généralisant les permutohèdres, décrivent le système de réécriture associé à la commutativité sur des mots finis, tandis que ces derniers sont étudies dans le context de la logique linéaire. Toutes ces structures ont une interpretation en tant que espaces dirigées, qui donnent une sémantique géométrique aux systèmes concurrents. Je montrerais que les types de homotopie dirigée de ces espaces ont un lien fort avec les congruences des treillis associés. Je terminerai par une description brève de l’usage de dualités topologiques dans ce travail en cours.
AOC 18/01/2024 Rule-based machine learning via mathematical optimization, par Cristina Molero del Río
Cristina Molero del Río, LIX - École Polytechnique  
Salle B107, bâtiment B, Université de Villetaneuse
18/01/2024    10:30 - 11:30
Résumé :
Rule-based machine learning models are appealing because of their simple decision structure. In this talk, we will present two examples, decision trees and rule sets, with special focus on the former. Contrary to classic classification and regression trees, built in a greedy heuristic manner, designing the tree model through an optimization problem allows us to easily include desirable properties in Machine Learning in addition to prediction accuracy. We present a Non-Linear Optimization approach that is scalable with respect to the size of the training sample, and illustrate this flexibility to model several important issues in Explainable and Fair Machine Learning. These include sparsity, as a proxy for interpretability, by reducing the amount of information necessary to predict well; fairness, by aiming to avoid predictions that discriminate against sensitive features such as gender or race; the cost-sensitivity for groups of individuals in which prediction errors are more critical, such as patients of a disease, by ensuring an acceptable accuracy performance for them; local explainability, where the goal is to identify the predictor variables that have the largest impact on the individual predictions; as well as data complexity in the form of observations of functional nature. The performance of our approach is illustrated on real and synthetic data sets
LOVE 11/01/2024 Focused orthogonality as denotations of circular and non-wellfounded proofs, par Farzad Jafarrahmani
Farzad Jafarrahmani, LIP6  
Salle B107, bâtiment B, Université de Villetaneuse
11/01/2024    10:30 - 11:30
Résumé :
This talk investigates the question of denotational invariants of non-wellfounded and circular proofs of the linear logic with least and greatest fixpoints. While non-wellfounded and circular proof theory has made significant progress in the last twenty years, the corresponding denotational semantics is still underdeveloped. First, we explore a theory of fixpoint constructions in focused orthogonality categories and present a lifting theorem for initial algebras and final coalgebras. These constructions crucially hinge on the insight that focused orthogonality categories are relational fibrations. We then demonstrate that assuming a CPO structure on our category allows the focused orthogonality construction to provide a model for non-wellfounded proofs. Several properties of the semantics will be discussed, including its soundness, the relationship between totality (orthogonality) and validity, and the semantic content involved in translating finitary proofs to circular proofs. Finally, the talk focuses on circular proofs, aiming to leverage their regularity to define the interpretation function inductively. We argue why the usual validity condition is too general for this purpose, while a fragment of circular proofs—strongly valid proofs—constitutes a well-behaved class for such an inductive interpretation.
LOVE 07/12/2023 Countable choice in Observational Type Theory, par Loïc Pujet
Loïc Pujet, University of Stockholm  
Salle B107, bâtiment B, Université de Villetaneuse
07/12/2023    10:30 - 11:30
Résumé :
Observational Type Theory is an internal language for types equipped with a proof-irrelevant propositional equality ("setoids"). As such, OTT natively supports extensionality principles, UIP, and quotients of types by proof-irrelevant relations (à la Lean). Unfortunately, it is difficult to use these quotients without any choice principles to extract information from proof-irrelevant propositions. In this talk, I will use ideas from Higher Observational Type Theory to sketch a version of OTT that supports countable choice for Delta00 predicates.
LOVE 30/11/2023 Exploring the Bang-Calculus and Its Embeddings , par Victor Arrial
Victor Arrial, IRIF  
Salle B107, bâtiment B, Université de Villetaneuse
30/11/2023    10:30 - 11:30
Résumé :
The Bang Calculus (BANG) has emerged as a powerful unifying framework for understanding and analyzing different evaluation strategies, particularly Call-by-Name (CBN) and Call-by-Value (CBV). This unification is achieved through the ingenious use of two fundamental primitives: "!" and "der" effectively pausing and resuming computations. This presentation delves into the heart of the dBANG Calculus –a variant of BANG where reduction acts at a distance– exploring its capacity to unify these paradigms. First, we will recall the dBANG calculus and present its two embeddings that adeptly capture the distant variants of CBN (dCBN) and CBV (dCBV), along with intersection type systems tailored to each of these calculi. Next, we shift our focus to the inhabitation problem, a minimal form of type-based program synthesis. We provide a comprehensive overview of the method we employ to address this problem, offering a correct and complete basis of all solutions through approximants. We will in particular explain the behaviours of such basis through the dCBN and dCBV embeddings, demonstrating how the inhabitation algorithm for dBANG elegantly tackles all three problems in a unified manner. While these embeddings seamlessly unify the static properties crucial for solving the inhabitation problem, it turns out that the dCBV embedding does not faithfully capture dynamical property. In response, we introduce novel dCBV embeddings that rectify this discrepancy. We achieve this by pinpointing a specific subset of reductions called diligent reductions, showcasing their ability to faithfully capture the dynamical properties of dCBV. We illustrate our methodology through a concrete application: factorizations for both dCBN and dCBV are derived from factorization in dBANG.
LOVE 09/11/2023 Finitary semantics and profinite lambda-terms, par Vincent Moreau
Vincent Moreau, IRIF  
Salle B107, bâtiment B, Université de Villetaneuse
09/11/2023    10:30 - 12:00
Résumé :
There is a growing connection between the simply typed lambda-calculus and automata theory. On the syntactic side, the Church encoding shows that finite words and trees can be seen as simply typed lambda-terms. On the semantic side, the interpretation of lambda-calculus into the CCC of finite sets and functions generalizes to the higher order the notion of run into a deterministic finite automaton. These observations have been fruitfully studied by Salvati to define a notion of regular language of lambda-terms. The limiting behavior of words with respect to finite automata gives rise to the notion of profinite word, whose space is the Stone dual of the algebra of regular language. Combining the ideas of Salvati and the topological approach to automata theory, we present in this talk a notion of profinite lambda-term which generalizes at every simple type the traditional notion of profinite word coming from automata theory. We elucidate their connection with Stone duality and parametricity à la Reynolds and demonstrate their relative independence from their initial construction.
AOC 09/11/2023 Submodular maximization of concave utility functions composed with a set-union operator with applications to maximal covering location problems, par Fabio Furini
Fabio Furini, Université Sapienza de Rome  
Salle D214, bâtiment D, Université de Villetaneuse
09/11/2023    10:30 - 11:30
Résumé :
We study a family of discrete optimization problems asking for the maximization of the expected value of a concave, strictly increasing, and differentiable function composed with a set-union operator. The expected value is computed with respect to a set of coefficients taking values from a discrete set of scenarios. The function models the utility function of the decision maker, while the set-union operator models a covering relationship between two ground sets, a set of items and a set of metaitems. This problem generalizes the problem introduced by Ahmed S, Atamtürk A (Mathematical programming 128(1-2):149–169, 2011), and it can be modeled as a mixed integer nonlinear program involving binary decision variables associated with the items and metaitems. Its goal is to find a subset of metaitems that maximizes the total utility corresponding to the items it covers. It has applications to, among others, maximal covering location, and influence maximization problems. In the paper, we propose a double-hypograph decomposition that allows for projecting out the variables associated with the items by separately exploiting the structural properties of the utility function and of the set-union operator. Thanks to it, the utility function is linearized via an exact outer-approximation technique, whereas the set-union operator is linearized in two ways: either (i) via a reformulation based on submodular cuts, or (ii) via a Benders decomposition. We analyze from a theoretical perspective the strength of the inequalities of the resulting reformulations and embed them into two branch-and-cut algorithms. We also show how to extend our reformulations to the case where the utility function is not necessarily increasing. We then experimentally compare our algorithms inter se, to a standard reformulation based on submodular cuts, to a state-of-the-art global-optimization solver, and to the greedy algorithm for the maximization of a submodular function. The results reveal that, on our testbed, the method based on combining an outer approximation with Benders cuts significantly outperforms the other ones.
RCLN 30/10/2023 On Semantic Annotation of Legislation, par Adam Wyner
Adam Wyner, Swansea University  
Salle B107, bâtiment B, Université de Villetaneuse
30/10/2023    12:30 - 13:30
Résumé :
The talk presents an overview of recent work on semantic annotation of legislation. The law is presented in a range of complex, dense texts. Querying and correlating laws would help individuals and organisations access, understand, and comply with their legal obligations. We first present the Core Legal Annotation Language (CLAL), a machine readable XML for key semantic elements such as obligations, prohibitions, exceptions, and others. CLAL is applied to the GDPR; we show some examples. We then turn to issues related to information retrieval from the annotated GDPR, particularly where implicitly related information is needed, e.g., obligations and rights. Finally, we step back and discuss general methodological issues. Currently, there is diversity amongst the metadata of legal texts. This is particularly problematic for the law, as it is desirable to have common resources in order to extract information or support inferences. To achieve this, we propose a methodology based on the notions of formalisation continuum, modularisation, and stepwise refinement.
AOC 26/10/2023 Binary non-negative polynomials and convex certificates, par Liding Xu
Liding Xu, LIX - École Polytechnique  
Salle A303, bâtiment A, Université de Villetaneuse
26/10/2023    10:30 - 11:30
Résumé :
We consider the problem of certifying the non-negativity of polynomials over the Boolean hypercube. We propose a new type of binary non-negativity certificate, which involves the signed support vector of the monomials occurring in the given polynomial. We employ known tools such as max flow and extensions of supermodular functions in order to construct our certificates. Especially, we examine the projected and extended LP formulations for the cone of our binary non-negativity certificates. Based on these tools, we show that a certain family of binary polynomials can be optimized in a fixed-parameter tractable way.
RCLN 23/10/2023 Towards a Formalisation of Value-based Actions and Consequentialist Ethics, par Adam Wyner
Adam Wyner, Swansea University  
Salle B107, bâtiment B, Université de Villetaneuse
23/10/2023    13:00 - 13:45
Résumé :
Agents act in ways that relate to their personal or institutional values, amongst other reasons to act; that is, Agents aim to bring about a state of the world that is more compatible with their values. To formalise and ground this intuition, the paper proposes an action framework based on the familiar STRIPS formalisation. The technical contribution is to express actions in terms of Value-based Formal Reasoning (VFR), which provides a set of propositions derived from an AgentÂ’s value profile and the AgentÂ’s assessment of propositions in light of the profile. The conceptual contribution is to provide a computational framework for a form of consequentialist ethics which is satisficing, pluralistic, act-based, and preferential.
RCLN 23/10/2023 L’ontologie pour la représentation des connaissances et la prise de décision pour les systèmes multi-capteurs de plateformes aéroportées, par Vincent Beugnet
Vincent Beugnet, LIPN + Thales  
Salle B107, bâtiment B, Université de Villetaneuse
23/10/2023    12:30 - 12:00
Résumé :
L’identification d’objets est un enjeu critique pour les plateformes aéroportées dans un contexte militaire. Les systèmes actuellement existants et utilisés ne permettent pas une identification automatique des objets rencontrés malgré l’augmentation des capacités des capteurs. Nous proposons un système basé sur des ontologies pour optimiser l’acquisition d’informations sur les objets rencontrés en prenant la main sur la suite de capteurs à disposition.
AOC 12/10/2023 Identification des préférences structurées en choix social : quelques résultats algorithmiques et expérimentaux, par Olivier Spanjaard
Olivier Spanjaard, LIP6-Sorbonne Université  
Salle B107, bâtiment B, Université de Villetaneuse
12/10/2023    10:30 - 11:30
Résumé :
Dans cet exposé, nous présenterons quelques résultats sur la reconnaissance de structures dans les préférences en décision collective. Plus précisément, étant donnée une collection de préférences de votants exprimées sous la forme de relations d'ordre complètes sur un même ensemble de candidats, on cherchera à déterminer si ses préférences respectent une structure commune sur les candidats, et si oui à identifier cette structure. Nous nous intéresserons au cas des préférences unimodales (single-peaked) sur un axe ou sur un graphe quelconque. Nous aborderons à la fois des aspects portant sur la justification de la pertinence des structures identifiées, des aspects algorithmiques et des aspects plus expérimentaux.
LOVE 05/10/2023 Normal Form Bisimulations by Value , par Adrienne Lancelot
Adrienne Lancelot, IRIF  
Salle B107, bâtiment B, Université de Villetaneuse
05/10/2023    10:30 - 11:30
Résumé :
Normal form bisimilarities are a natural form of program equivalence resting on open terms, first introduced by Sangiorgi in call-by-name. The literature contains a normal form bisimilarity for Plotkin’s call-by-value lambda-calculus, Lassen’s enf bisimilarity, which validates all of Moggi’s monadic laws and can be extended to validate eta. It does not validate, however, other relevant principles, such as the identification of meaningless terms—validated instead by Sangiorgi’s bisimilarity—or the commutation of lets. These shortcomings are due to issues with open terms of Plotkin’s calculus. We introduce a new call-by-value normal form bisimilarity, deemed net bisimilarity, closer in spirit to Sangiorgi’s and satisfying the additional principles. We develop it on top of an existing formalism designed for dealing with open terms in call-by-value. It turns out that enf and net bisimilarities are incomparable, as net bisimilarity does not validate Moggi’s laws nor eta. Moreover, there is no easy way to merge them. To better understand the situation, we provide an analysis of the rich range of possible call-by-value normal form bisimilarities, relating them to Ehrhard’s relational model.
LOVE 22/09/2023 Theoretical and algorithmic contributions to the analysis of safety and security properties in timed systems under uncertainty, par Dylan Marinho
Dylan Marinho, Université de Lorraine  
Salle B107, bâtiment B, Université de Villetaneuse [BBB: https://bbb.lipn.univ-paris13.fr/b/ari-uht-t3u]
22/09/2023    12:15 - 13:15
Résumé :
Real-time systems can be used in a wide range of applications, such as transport, telecommunications and industry. However, accidents can happen, and it is necessary to have confidence in these systems in order to avoid them. It is therefore necessary to formally prove that their behavior will comply with a specification. This specification can be of two kinds: with safety properties, showing that the system will always behave as expected, and security properties, showing that it will be resistant to certain attacks. For this, the formalism of timed automata (TAs) is fairly common.
LOVE 21/09/2023 Relative monads and distributors, par Nathanael Arkor
Nathanael Arkor, https://arkor.co/  
Salle B107, bâtiment B, Université de Villetaneuse
21/09/2023    10:30 - 12:00
Résumé :
One of the oldest and most fundamental concepts in category theory is that of a monad, which may be viewed as an axiomatisation of free constructions. More recently, it has become increasingly evident that a natural generalisation, the concept of a relative monad, is even more fundamental. Relative monads generalise monads by permitting the axiomatisation of situations in which not every object admits a free construction. While there is already much evidence that relative monads will be an invaluable tool in category theory and its applications in the years to come, the theory of relative monads remains relatively undeveloped compared to the classical theory of monads. As a step towards furthering our understanding of relative monads, in this talk, I will explore the connection between relative monads and the theory of distributors. Distributors may be viewed as a categorified notion of relation, in the same way that functors may be viewed as a categorified notion of function. While categories, functors, and natural transformations are generally viewed as the basic structure of category theory, I will argue that distributors ought also to be viewed on the same footing. To justify this, I will show how many important aspects of the theory of relative monads (and consequently also non-relative monads) follow from the theory of distributors, and give several examples arising from pure category theory and categorical logic. A particular advantage of the distributor-based approach is its amenability to formalisation in the sense of formal category theory, and I will spend a little time explaining how, by working in the context of a virtual double category, we may capture analogous results for enriched relative monads, internal relative monads, and so on, with little extra work. For this talk, I will assume some basic knowledge of category theory, but will not assume familiarity with relative monads or with distributors. The talk is based on forthcoming joint work with Dylan McDermott.
AOC 21/09/2023 Theoretical and Computational comparison of Perspective Formulations for Piecewise Convex Problems, par Claudia DÂ’ambrosio
Claudia DÂ’ambrosio, LIX - école polytechnique  
Salle C216, bâtiment C, Université de Villetaneuse
21/09/2023    10:30 - 11:30
Résumé :
Our study aims to generalize mathematical formulations for Piecewise Linear functions to Piecewise Convex functions, when they appears as part of mathematical optimization problems. In this seminar, we compare different formulations and show that their continuous relaxations are not equivalent when perspective reformulation is applied to strengthen the formulation of each single segment where the function is convex. Computational results on some classes of piecewise convex problems are presented
LOVE 14/09/2023 Universal Quantitative Algebra, par Ralph Sarkis
Ralph Sarkis, ENS Lyon  
Salle B107, bâtiment B, Université de Villetaneuse
14/09/2023    10:30 - 11:30
Résumé :
Universal algebra and equational logic stand as well-established tools for reasoning about programs and program equivalences. Universal quantitative algebra and quantitative equational logic were introduced as a natural extension of these to reason about program distances. A central result in the classical realm is the correspondence between algebraic theories and (finitary) monads on the category Set. While a complete axiomatization of quantitative algebraic theories remains out of reach, we show every lifting of a monad on Set with an algebraic presentation can be presented by a quantitative algebraic theory. This result encompasses all currently known applications.
LOVE 07/09/2023 Strategies as Resource Terms, and their Categorical Semantics , par Lison Blondeau-Patissier
Lison Blondeau-Patissier, LIS, Marseille  
Salle B107, bâtiment B, Université de Villetaneuse
07/09/2023    10:30 - 11:30
Résumé :
As shown by Tsukada and Ong, normal (extensional) simply-typed resource terms correspond to plays in Hyland-Ong games, quotiented by Melliès' homotopy equivalence. Though inspiring, their proof is indirect, relying on the injectivity of the relational model w.r.t. both sides of the correspondence - in particular, the dynamics of the resource calculus is taken into account only via the compatibility of the relational model with the composition of normal terms defined by normalization. In the present talk, we revisit and extend these results. Our first contribution is to restate the correspondence by considering causal structures we call augmentations, which are canonical representatives of Hyland-Ong plays up to homotopy. This allows us to give a direct and explicit account of the connection with normal resource terms. As a second contribution, we extend this account to the reduction of resource terms: building on a notion of strategies as weighted sums of augmentations, we provide a denotational model of the resource calculus, invariant under reduction. A key step - and our third contribution - is a categorical model we call a resource category, which is to the resource calculus what differential categories are to the differential {\lambda}-calculus. This is a joint work with Pierre Clairambault and Lionel Vaux Auclair.
RCLN 03/07/2023 A family of contrast-pattern based classifiers for class-imbalance problems, par Raul Monroy
Raul Monroy, Tecnologico de Monterrey  
Salle B107, bâtiment B, Université de Villetaneuse
03/07/2023    12:30 - 13:30
Résumé :
In this talk, I will give an overview of a family of contrast-pattern based classification mechanisms, especially designed to deal with class-imbalance problems. In particular, I will go into the internal workings of three classifiers, namely: PBC4cip, MHLDT and FT4cip. I will highlight pros and cons, as well as giving an outline of some greatest hits.
RCLN 26/06/2023 ChêneTAL. Plateforme d’expérimentation sur des outils de traitement automatique des langues et d’intelligence artificielle, par Othman Boudarga
Othman Boudarga, USPN  
Salle B107, bâtiment B, Université de Villetaneuse
26/06/2023    12:00 - 13:00
Résumé :
La plateforme CheneTAL a été conçue pour permettre la mise en place de chaînes hétérogènes de Traitement Automatique des Langues (TAL) en intégrant des logiciels existants en gestion et manipulation de corpus avec des modèles plus récents d’Intelligence Artificielle (IA), tout en gardant une interface simplifiée qui permette son utilisation et par les chercheur·euse·s de la communauté de Traitement Automatique des Langues (TAL) et par des chercheur·euse·s en Linguistique/Sciences Humaines et Sociales non experts en informatique. Pendant le séminaire, une première version fonctionnelle de la plateforme sera présentée.
AOC 22/06/2023 A Polyhedral Approach to the Total Matching Problem, par Luca Ferrarini
Luca Ferrarini, ENPC  
Salle B107, bâtiment B, Université de Villetaneuse
22/06/2023    10:30 - 11:30
Résumé :
A total matching of a graph G = (V, E) is a subset of G such that its elements, i.e. vertices and edges, are pairwise, not adjacent. In this context, the Total Matching Problem calls for a total matching of maximum size. This problem generalizes both the Stable Set Problem, where we look for a stable set of the maximum size, and the Matching Problem, where instead we look for a matching of maximum size. In this talk, we present a polyhedral approach to the Total Matching Problem, and hence, we introduce the corresponding polytope, namely the Total Matching Polytope. To this end, we will present several families of nontrivial valid inequalities which are facet-defining for the Total Matching Polytope. In addition, we provide a first linear complete description for trees and complete bipartite graphs. For the latter family, the complete characterization is obtained by projecting a higher-dimension polytope onto the original space. This leads to also give an extended formulation of compact size for the Total Matching Polytope of complete bipartite graphs.
AOC 15/06/2023 Decision support models for the extended producer, par Pablo Andrés Maya
Pablo Andrés Maya, Universidad de Antioquia  
Salle B107, bâtiment B, Université de Villetaneuse
15/06/2023    10:30 - 11:30
Résumé :
Extended Producer Responsibility (EPR) is an environmental policy instrument that mandates producers to assume responsibility for the entire life cycle of their products, encompassing production, commercialization, recovery, and final disposal. Operations Management (OM) and supply chain (SC) play pivotal roles in enabling circular strategies that facilitate the achievement of EPR objectives. This presentation aims to emphasize the primary challenges that must be addressed, along with the potential contribution of decision support models in overcoming them.
LOVE 12/05/2023 MUPPAAL: Reducing and Removing Equivalent and Duplicate Mutants in UPPAAL, par James Ortiz
James Ortiz, Université de Namur  
Salle B107, bâtiment B, Université de Villetaneuse
12/05/2023    12:15 - 13:15
Résumé :
Mutation Testing (MT) is a test quality assessment technique that creates mutants by injecting artificial faults into the system and evaluating the ability of tests to distinguish these mutants. We focus on MT for safety-critical Timed Automata (TA). MT is prone to equivalent and duplicate mutants, the former having the same behaviour as the original system and the latter other mutants. Such mutants bring no value and induce useless test case executions. We propose MUPPAAL, a tool that: (1) offers a new operator reducing the occurrence of mutant duplicates; (2) an efficient bisimulation algorithm removing remaining duplicates; (3) leverages existing equivalence-avoiding mutation operators. Our experiments on four UPPAAL case studies indicate that duplicates represent up to 32% of all mutants and that the MUPPAAL bisimulation algorithm can identify them more than 99% of the time.
LOVE 13/04/2023 The cartesian closed bicategory of thin spans , par Simon Forest
Simon Forest, Aix-Marseille Université  
Salle B107, bâtiment B, Université de Villetaneuse
13/04/2023    10:30 - 11:30
Résumé :
In the Rel model of linear logic, types are interpreted by sets, and proofs/programs by relations. A natural idea to have a quantitative, or proof-relevant model (i.e. a model that keeps distinct the different executions giving rise to the same observable result), is to use spans instead of relations. Indeed the (bi)category Span, whose morphisms are spans of sets composed by pullbacks, can be seen as a proof-relevant analogue: where a relation between A and B keeps only binary information (if a and b are related), a span associates to all a and b a set of witnesses, or "proofs" that they are related. Unfortunately, a naive adaptation of exponential on Rel does not work on Span. Other works, such as those on generalized species of structure, provide proof-relevant models, but where the composition requires a complex quotient of the witnesses, thus lacking the "concrete" aspect of the pullback. Although a quotient seems unavoidable, another model, the one of "thin concurrent games", involves a concrete composition, without quotient. By adapting the techniques used in the latter model, this work gives good results in the direction of a span model of LL, where the composition is done by classical pullbacks. In particular, it is shown that, for an adequate pseudocomonad on spans, we obtain a cartesian closed co-Kleisli bicategory.
AOC 04/04/2023 Reformulations pour l'optimisation convexe par morceaux, par Renan Spencer Trindade
Renan Spencer Trindade, LIX - Ecole Polythecnique  
Salle B107, bâtiment B, Université de Villetaneuse
04/04/2023    10:30 - 11:30
Résumé :
La programmation non linéaire en nombres entiers (PNLNE) a fait l'objet d'une attention croissante de la part des chercheurs ces dernières années en raison de sa capacité à modéliser une grande variété d'applications dans le monde réel. Cependant, obtenir un optimum global d'un problème PNLNEs non convexes reste très difficile. Il est donc primordial d'exploiter, quand possible, toutes les propriétés mathématiques des PNLNE qu'on souhaite résoudre. Notre étude est motivée par la résolution de PNLNE lorsque le non-convexité se manifeste par la somme de fonctions univariées non convexes. Nous proposons une méthode basée sur des relations PNLNE convexes, obtenues en traitant séparément les intervalles où chaque fonction univariée est convexe ou concave. Dans la relaxation PNLNE convexe, chaque intervalle concave est remplacé par une linéarisation par morceaux. Pour résoudre le PNLNE résultant, nous utilisons une méthode de plans coupants qui utilise des coupes perspectives. Pour atteindre l'optimum globale, la précision de la relaxation de l'intervalle concave est incrémentée de manière itérative. Ce processus nécessite l'introduction de nouvelles variables binaires pour l'activation des intervalles dans lesquels les fonctions sont définies. Toutefois, cette étape de reformulation peut en fait être réalisée de différentes manières. Dans notre travail, nous comparons les trois différentes formulations classiques tant sur le plan théorique que sur le plan pratique. Nous prouvons que, contrairement au cas linéaire, les formulations ne sont pas équivalentes lorsque la reformulation en perspective est appliquée. Nous montrons l'impact des différentes formulations par des résultats de calcul.
AOC 23/03/2023 Exact algorithms for linear matrix inequalities and application to the moment problem, par Simone Naldi
Simone Naldi, Université de Limoges  
Salle B107, bâtiment B, Université de Villetaneuse
23/03/2023    10:30 - 11:30
Résumé :
In this talk I will discuss computer algebra algorithms for solving exactly linear matrix inequalities, that is, the feasibility of a semidefinite program. These algorithms rely on the determinantal structure behind SDP. The main motivation is for certifying lower bounds in polynomial optimization, for instance, for computing the sum of squares certificates of multivariate polynomials. Recently a new application to the so-called truncated moment problem gives new perspectives that will be discussed in the second part of the talk. This consists of the decision problem whether a sequence of real numbers, indexed by monomials of degree d in n variables, is the moment sequence of a nonnegative Borel measure with support in some basic semialgebraic set. This is based on joint work with D. Henrion and M. Safey El Din.
AOC 22/03/2023 Two non-linear stochastic problems with catastrophic consequences, par Alberto Santini
Alberto Santini, ESSEC  
Salle B107, bâtiment B, Université de Villetaneuse
22/03/2023    10:30 - 11:30
Résumé :
We study two stochastic problems in which some events occur with low probability but can have catastrophic consequences. The first is the 0-1 Time-bomb Knapsack Problem, an extension of the classical Knapsack Problem in which each item has an associated probability of exploding and destroying the entire content of the knapsack. The objective is to maximise the expected profit of the selected items. The second is the Hazardous Orienteering Problem (HOP), which extends the classical Orienteering Problem. In the HOP, the vehicle picks up parcels at the customers it visits. Some of these parcels have a probability of exploding and destroying the entire content of the vehicle. This probability depends on the amount of time the parcel spends on board the vehicle, following an exponential distribution. The objective is again to maximise the expected collected profit. We propose mathematical formulations and valid inequalities, exact algorithms based on branch-and-bound and dynamic programming, and primal and dual bounding techniques for both problems.
RCLN 20/03/2023 From Language Models to (very) Large Language Models, par Davide Buscaldi
Davide Buscaldi, LIPN (équipe RCLN)  
Salle B107, bâtiment B, Université de Villetaneuse
20/03/2023    12:30 - 14:30
Résumé :
Originairement destiné à l'équipe RCLN, je propose ce séminaire pour tous les curieux sur les derniers modèles de langage, BERT, GPT, GPT-2, GPT-3, GPT-4 et bien sûr chatGPT. J'ai ciblé la presentation pour couvrir aussi les bases des modèles de langage pour comprendre le fonctionnement de ces modèles à plus bas niveau.
LOVE 17/03/2023 Weak omega-categories and their internal language in dependent type theory, par Thibaut Benjamin
Thibaut Benjamin, CEA List  
Salle B107, bâtiment B, Université de Villetaneuse
17/03/2023    14:00 - 15:00
Résumé :
Weak omega-categories are one of the most difficult algebraic structures to define and study, because of the large number axioms that they require. I will present the language CaTT, introduced by Finster and Mimram in order to describe weak omega-categories. I will first use an implementation of the theory to write a few definition in this language, in order to provide intuition on the kind of structure that we consider and get used to the language. Then I will describe this language formally as a dependent type theory and hint at a formal presentation of weak omega-category. Finally I will discuss a few improvements that can be made to the language and relate the syntactic manipulations to the semantic interpretation in weak omega-category theory
LOVE 16/03/2023 Knowledge and Topology: Simplicial Models for Epistemic Logic, par Jérémy Ledent
Jérémy Ledent, University of Strathclyde  
Salle B107, bâtiment B, Université de Villetaneuse
16/03/2023    10:30 - 11:30
Résumé :
Multi-agent Epistemic Logic is a modal logic of knowledge. It allows to reason about a finite set of agents who may know facts about the world, and about each other. In this talk, I will present a new semantics for epistemic logic, based on simplicial complexes. In this approach, the knowledge of the agents is modeled by a higher-dimensional space called a simplicial model; and the satisfaction of an epistemic logic formula can be evaluated by inspecting the various possible paths in this space. I will illustrate these ideas using examples from the theory of distributed computing, where the agents correspond to processes that can exchange information in order to solve a task. Both topological invariants and logical invariants can be leveraged to prove that some distributed computing tasks are impossible to solve.
AOC 16/03/2023 Robust min-max regret covering problems, par Amadeu Almeida Coco
Amadeu Almeida Coco  
Salle B107, bâtiment B, Université de Villetaneuse
16/03/2023    10:30 - 10:30
Résumé :
This presentation discusses two min-max regret covering problems: the min-max regret Weighted Set Covering Problem (min-max regret WSCP) and the min-max regret Maximum Benefit Set Covering Problem (min-max regret MSCP). These problems are the robust optimization counterparts, respectively, of the Weighted Set Covering Problem and of the Maximum Benefit Set Covering Problem. In both problems, uncertainty in data is modeled by using an interval of continuous values, representing all the infinite values every uncertain parameter can assume. This study has the following major contributions: (i) a proof that MSCP is ?p2-Hard, (ii) a mathematical formulation for the min-max regret WSCP, (iii) exact and (iv) heuristic algorithms for the min-max regret WSCP and the min-max regret MSCP. We reproduce the main exact algorithms for the min-max regret WSCP found in the literature: a Logic-based Benders decomposition, an extended Benders decomposition, and a branch-and-cut. In addition, such algorithms have been adapted for the min-max regret MSCP. Moreover, five heuristics are applied for both problems: two scenario-based heuristics, a path relinking, a pilot method, and a linear programming-based heuristic. The goal is to analyze the impact of such methods on handling robust covering problems in terms of solution quality and performance.
AOC 10/03/2023 Partial Optimality in Cubic Correlation Clustering, par Silvia Di Gregorio
Silvia Di Gregorio, Faculty of Computer Science TU Dresden  
Visio - https://bbb.lipn.univ-paris13.fr/b/wol-ma9-vjn - 514019
10/03/2023    12:00 - 13:00
Résumé :
The higher-order correlation clustering problem is an expressive model, and recently, local search heuristics have been proposed for several applications. Certifying optimality, however, is NP-hard and practically hampered already by the complexity of the problem statement. Here, we focus on establishing partial optimality conditions for the special case of complete graphs and cubic objective functions. In addition, we define and implement algorithms for testing these conditions and examine their effect numerically, on two datasets.
AOC 09/03/2023 Catégories de sommets pour le problème de domination , par Vincent Bouquet
Vincent Bouquet, CNAM  
Salle B107, bâtiment B, Université de Villetaneuse
09/03/2023    10:30 - 11:30
Résumé :
Cette présentation porte sur les sommets qui appartiennent à tous les ensembles dominants minimums d'un graphe. Nous caractérisons ces sommets en fonction de leur criticité relativement au nombre de domination. Cette criticité mesure comment le retrait d'un sommet du graphe affecte le nombre de domination. Nous nous intéressons ensuite à cette caractérisation dans quelques classes de graphes: les graphes triangulés, les cographes, ainsi que des sous-classes des graphes sans griffe. Pour ces graphes, nous montrons que les sommets persistants sont toujours critiques: c'est-à-dire que le retrait d'un sommet persistant fait augmenter le nombre de domination.
COMP 06/03/2023 Operator Scaling II, par Thomas Seiller
Thomas Seiller, CNRS, LIPN  
Hybride (Salle B107 et https://bbb.lipn.univ-paris13.fr/b/sei-nlh-8vr-xvy)
06/03/2023    14:30 - 16:00
Résumé :
COMP 27/02/2023 Random SAT, par Alexandros Singh
Alexandros Singh, LIPN  
Hybride (Salle B107 et https://bbb.lipn.univ-paris13.fr/b/sei-nlh-8vr-xvy)
27/02/2023    14:30 - 16:00
Résumé :
COMP 20/02/2023 Descriptive Complexity, par Paulin de Naurois
Paulin de Naurois, CNRS, LIPN  
Hybride (Salle B107 et https://bbb.lipn.univ-paris13.fr/b/sei-nlh-8vr-xvy)
20/02/2023    14:30 - 16:00
Résumé :
AOC 16/02/2023 Multiplicité dans le partitionnement de graphes signés, par Nejat Arinik
Nejat Arinik, INRAE  
Salle B107, bâtiment B, Université de Villetaneuse
16/02/2023    10:30 - 11:30
Résumé :
Selon la théorie de l'équilibre structural, un graphe signé est structurellement équilibré s'il peut être partitionné en sous-groupes mutuellement hostiles (i.e. reliés seulement par des liens négatifs) tout en exhibant une solidarité interne (i.e. contenant uniquement des liens positifs). Mais un réseau réel (i.e. un graphe représentant un système du monde réel) est rarement parfaitement équilibré : on trouvera quelques liens positifs entre les groupes et/ou quelques liens négatifs à l'intérieur de certains groupes. L'un des défis du domaine est de quantifier le niveau de déséquilibre d'un tel réseau et d'identifier les liens qui causent ce déséquilibre. Le problème Correlation Clustering (CC) se définit précisément par l'obtention d'une partition possédant un déséquilibre minimal. Le partitionnement de graphes signés constitue une tâche importante du point de vue applicatif, étant donné que trouver une partition équilibrée aide à comprendre le système modélisé par le graphe signé. Cependant, l'approche standard dans la littérature se contente de chercher une seule partition, comme si elle caractérisait suffisamment le système étudié. Or, on peut avoir besoin de plusieurs partitions pour construire une image plus juste du système étudié. Même si cette notion de la multiplicité est extrêmement important du point de vue des utilisateurs finaux, elle a été très peu abordée dans la littérature. Une particulière situation dans laquelle on veut relaxer l'hypothèse de partition unique et en chercher plusieurs est lié au problème CC. Quand on résout une instance de ce problème, plusieurs partitions optimales peuvent coexister. La question qui se pose est de savoir ce qu'on perd, si on considère une seule partition optimale, alors qu'il en existe plusieurs. Idéalement, il faut les énumérer toutes avant de faire une analyse concluante. Pour ce faire, on propose une nouvelle méthode d'énumération et un framework basé sur l'analyse de clustering afin de d'abord complètement énumérer l'espace des partitions optimales, puis étudier empiriquement un tel espace. Nos résultats ont révélé une typologie de l'espace de partitions optimales : 1) une seule partition optimale ; 2) quelques partitions constituant une seule classe ; 3) beaucoup de partitions optimales constituant une seule classe de forme allongée ; 4) plusieurs partitions optimales constituant plusieurs classes de partitions.
RCLN 13/02/2023 Towards Detecting Pre-training Data Set Manipulations: the Need to Build Efficient Language Models, par Wissam Antoun
Wissam Antoun, INRIA  
Salle B107, bâtiment B, Université de Villetaneuse
13/02/2023    12:30 - 13:30
Résumé :
The high compute cost required to train Large Language Models (LLMs) makes them only available to a hand full of high-budget private institutions, and countries. These institutions rarely documented their training data nor the data collection and filtering source code, thus raising questions about potential vulnerabilities of models that have been trained on them. For example, one of the many ways to inject adversarial biases and temper with training data is to produce machine-generated text carrying out these biases and have them included in the training data. So the matter of robust detection of machine-generated text is becoming crucial. Answering these questions first requires efficient ways to iterate and train language models quickly. In this talk, I will present my work on pretraining language models for Arabic and French and showcase the lessons learned in designing and training efficient LLMs. In particular, I'll talk about training AraBERT, AraELECTRA, AraGPT2, the current largest Transformer-based models for Arabic, and the AraGPT2 detector. I’ll also introduce CamemBERTa, a new sample-efficient language model for French, the first publicly available DeBERTa V3-based model outside of the original paper and which establishes a new SOTA for this language in many tasks. (Joint work with Benoit Sagot and Djamé Seddah, at the Inria’s Almanach team project)
LOVE 09/02/2023 Non-deterministic abstract machines, par Sergueï Lenglet
Sergueï Lenglet, Loria, Université de Lorraine  
Salle B107, bâtiment B, Université de Villetaneuse
09/02/2023    10:30 - 11:30
Résumé :
We present a generic design of abstract machines for non-deterministic programming languages such as process calculi or concurrent lambda calculi. Such a machine traverses a term in the search for a redex, making non-deterministic choices when several paths are possible and backtracking when it reaches a dead end, i.e., an irreducible subterm. The search is guaranteed to terminate thanks to term annotations the machine introduces along the way. We show how to automatically derive a non-deterministic abstract machine from a zipper semantics - a form of structural operational semantics in which the decomposition process of a term into a context and a redex is made explicit. The derivation method ensures the soundness and completeness of the machines w.r.t. the zipper semantics.
AOC 09/02/2023 QP/NLP-based Branch-and-Bound algorithm for MINLP: It could work! , par Luca Mencarelli
Luca Mencarelli, ENSTA  
Salle B107, bâtiment B, Université de Villetaneuse
09/02/2023    10:30 - 11:30
Résumé :
We describe a novel QP/NLP-based Branch-and-Bound algorithm for convex MINLP. Then, we introduce a tailored version of the previous algorithm for (non-convex) Binary Nonlinear Optimization Problems (BNPs), relying on a simple convexification procedure and a tailor convex quadratic under-approximation. We survey computational experiences on convex instances of MINLPLib and on several literature and random generated instances for BNPs.
AOC 08/02/2023 Hamiltonian degree condition for tough graphs, par Cleophee Robin
Cleophee Robin, Université de Montreal Canada  
https://bbb.lipn.univ-paris13.fr/b/wol-ma9-vjn - code: 514019
08/02/2023    16:00 - 17:00
Document attaché
Résumé :
A graph G is hamiltonian if there exists a G cycle containing all G vertices exactly once. A graph G is t-tough if, for all subsets of vertices S, the number of connected components in G-S is at most |S|/t. We extended the Theorem of Hoàng by proving the following: Let G be a graph with degree sequence d_1,d_2, ..., d_n, and let t be a positive integer at most 4. If G is a t-tough and if for each i, t <= i < n/2, d_i <= i --> d_{n-i+t} >= (n - i) then G is hamiltonian. To do this we extend the closure lemma due to Bondy and Chvàtal.
LOVE 02/02/2023 Call-by-value in bicategories of games , par Hugo Paquet
Hugo Paquet, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
02/02/2023    10:30 - 11:30
Résumé :
Game semantics is naturally described using a bicategory, rather than a category, because the composition of strategies is only associative and unital up to isomorphism. This makes it difficult to relate game semantics to the categorical theories of effects and resources, developed by Moggi, Melliès, and many others. In this talk I will describe new notions in bicategory theory: strong pseudomonads and premonoidal bicategories, that can be used for the semantics of call-by-value languages. As the main motivating example, I will discuss the bicategorical structure of game semantics and the universal properties that we can use to prove the coherence axioms. This is based on joint work with Philip Saville.
COMP 30/01/2023 Matrix scaling I, par Thomas Seiller
Thomas Seiller, CNRS, LIPN  
Hybride (Salle B107 & https://bbb.lipn.univ-paris13.fr/b/sei-nlh-8vr-xvy)
30/01/2023    14:30 - 16:00
Résumé :
I will talk about matrix/ operator scaling and how it relates to perfect matchings and polynomial identity testing.
COMP 16/01/2023 Optimisation problems, par Bruno Escoffier
Bruno Escoffier, LIP6  
Hybride (Salle B107 et https://bbb.lipn.univ-paris13.fr/b/sei-nlh-8vr-xvy)
16/01/2023    14:30 - 15:30
Résumé :
LOVE 12/01/2023 Introduction to Coherent Differentiation, par Aymeric Walch
Aymeric Walch, IRIF  
Salle B107, bâtiment B, Université de Villetaneuse
12/01/2023    10:00 - 12:00
Résumé :
The differential lambda calculus was introduced by Ehrhard and Reigner, following from the discovery of finitness spaces by Ehrhard. In those models of linear logic, a morphism !X -> Y can be seen as an analytic function. Analytic functions can always be written as an infinite sum involving the interrated derivatives (in the sense of the usual differential calculus) thanks to the so called Taylor Expansion. Ehrhard and Reigner transposed those ideas on the syntactic side. They introduced a syntactical notion of differentiation, corresponding to a notion of substitution in which only one occurence of a variable is replaced. They also introduced a syntactical counterpart for Taylor expansion. The major issue of differential calculus though is its non determinism, embodied by the Leibniz rule of differential calculus. There a multiple ways to substitute exactly one occurrence of a variable inside a given term. This non deterministic choice is represented by the use of formal sums and, on the side of models, the category is required to be additive (that is, enriched over commutative monoids). It leaves behind many models of LL, such as coherence spaces and probabilistic coherent spaces. Coherent Differentiation was introduced by Ehrhard in 2021 in order to solve those issues. In coherent differentiation, two morphisms are not always assumed to be summable. Interestingly, the notion of summability can be seen as some kind of strong Monad on the category, and the axioms of differentiation turn out to be necessary and sufficient conditions that allows to extends this Monad to the co-Kleisli category of the exponential. The goal of this talk is to introduce those ideas, with an emphasis on how coherent differentiation is a conservative extension of differential logic.
LOVE 15/12/2022 Synchronous and spatialized computations with Global Transformations, par Alexandre Fernandez
Alexandre Fernandez, ENS Lyon  
Salle B107, bâtiment B, Université de Villetaneuse
15/12/2022    10:30 - 12:00
Résumé :
This presentation outlines some ideas of my PhD about Global Transformations. These form a general method to describe local and synchronous spatialized dynamical systems such as Cellular Automata and Lindenmayer systems. This work originated from the goal of extending such systems to dynamical graphs. This talk first introduces the categorical formalism, and providing examples of such systems over different structures such as words or graphs. It also give simple instances of many categorical constructions, such as comma categories, colimits and Kan extensions. These tools are then used to relate the local specification of a system and its global behavior. The extension of this formalism to non-deterministic computations is then considered.
COMP 12/12/2022 On the weakness of logarithmic depth algebraic circuits, par Ulysse Léchine
Ulysse Léchine, LIPN, Université Paris 13  
Salle B107 et https://bbb.lipn.univ-paris13.fr/b/sei-nlh-8vr-xvy
12/12/2022    16:00 - 16:30
Résumé :
Talk planned as part of the ANR DySCo launch meeting.
COMP 12/12/2022 Lower bounds in Algebraic complexity, par Sébastien Tavenas
Sébastien Tavenas, CNRS, LAMA (Université Savoie Mont-Blanc)  
Salle B107 et https://bbb.lipn.univ-paris13.fr/b/sei-nlh-8vr-xvy
12/12/2022    14:30 - 15:30
Résumé :
Talk planned as part of the ANR DySCo launch meeting.
LOVE 09/12/2022 Vers des Processus Métier Corrects basés sur la Blockchain, par Ikram Garfatta
Ikram Garfatta, Équipe LoVe, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
09/12/2022    12:30 - 13:30
Résumé :
Plusieurs caractéristiques de la technologie Blockchain sont bien alignées sur des questions critiques dans le domaine de la gestion des processus métier (BPM), et pourtant l'adoption de Blockchain pour le BPM ne doit pas être prise à la légère. En effet, la sécurité des contrats intelligents, qui sont l'un des principaux éléments de la blockchain rendant possible son intégration avec le domaine BPM, s'est révélée vulnérable. Il est donc crucial pour la protection des processus métier conçus de prouver l'exactitude des contrats intelligents à déployer sur une blockchain. Dans cet exposé, je présenterai les travaux qui ont été menés au cours de ma thèse de doctorat, et dont l'objectif est d'apporter des contributions dans le contexte susmentionné. En effet, nous proposons une approche formelle basée sur la transformation des contrats intelligents Solidity, en tenant compte du contexte BPM dans lequel ils sont utilisés, en un réseau de Petri coloré hiérarchique. Nous exprimons un ensemble de vulnérabilités des contrats intelligents sous forme de formules de la logique temporelle linéaire et utilisons le vérificateur de modèle Helena non seulement pour détecter ces vulnérabilités tout en discernant leur exploitabilité, mais aussi pour vérifier d'autres propriétés spécifiques aux contrats. L'approche que nous proposons est basée sur la vérification des modèles CPN et comprend principalement trois phases : 1) la transformation du code Solidity des contrats intelligents en sous-modèles CPN correspondant à leurs fonctions. 2) transformer le contexte BPM en un modèle CPN 3) la construction d'un modèle CPN en fonction d'une propriété LTL qui peut exprimer : i) une vulnérabilité dans le code, ou ii) une propriété spécifique au contrat, en le reliant à un modèle CPN représentant le comportement à considérer, et l'utilisation du vérificateur de modèles pour vérifier la propriété ciblée sur le modèle construit.
LOVE 08/12/2022 Bidirectional Typing : From a Nice Implementation Technique to a Powerful Theoretical Tool, par Meven Lennon-Bertrand
Meven Lennon-Bertrand, University of Cambridge  
Salle B107, bâtiment B, Université de Villetaneuse
08/12/2022    14:00 - 15:00
Résumé :
In 2000, Pierce and Turner introduced a new technique called local type inference, to perform type inference for ML-like languages. The key idea was to carefully understand the flow of information in a typing derivation. This idea was not isolated: similar techniques had appeared independently in quite a few other contexts. The general idea, which came to be referred to as bidirectional typing, was in particular a cornerstore idea in the folklore of implementers of dependently typed languages. But it turns out that bidirectional typing is not just a nice implementation technique. It is also an interesting theoretical tool when working on the properties of type systems. In this talk, I will try and give some of my understanding of bidirectional typing, and how it can be used to make the infamously difficult meta-theory of dependent type systems a bit less difficult.
LOVE 02/12/2022 Exploring a Parallel SCC Algorithm: Using TLA+ and the TLC Model Checker, par Jaco van de Pol
Jaco van de Pol, Aarhus University + University of Twente  
Salle B107, bâtiment B, Université de Villetaneuse
02/12/2022    13:15 - 14:00
Résumé :
We explore a parallel SCC-decomposition algorithm based on a concurrent Union-Find data structure. In order to increase confidence in the algorithm, it is modelled in TLA+. The TLC model checker is used to demonstrate that it works correctly for all possible interleavings of two workers on a number of small input graphs. To increase the understanding of the algorithm, we investigate some potential invariants. Some of these are refuted, revealing that the algorithm allows suboptimal (but still correct) executions. Finally, we investigate some modifications of the algorithm. It turns out that most modifications lead to an incorrect algorithm, as revealed by the TLC model checker. We view this exploration as a first step to a full understanding and a rigorous correctness proof based on invariants or step-wise refinement. As ongoing work, we try to verify the correctness of the algorithm for any number of workers on any input graph, using the TLPAM proof manager.
LOVE 02/12/2022 A Rewriting Logic Semantics and Statistical Analysis for Probabilistic Event-B, par Daniel Osorio
Daniel Osorio, Équipe LoVe, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
02/12/2022    12:15 - 13:00
Résumé :
Formal methods provide a general structure for specifying real world systems as abstract models with mathematical rigor, that can be proven to be correct and implemented as specific pieces of software or hardware. Some systems must operate amid uncertain information, hence the need for probabilistic models where specific behaviors can be proved to be present or absent up to a certain confidence threshold. Event-B is a proof-based formal method for discrete systems modeling, and it has been extended to cope with probabilistic behaviors. To be able to do simulations and probabilistic temporal verification of probabilistic Event-B models, we present a rewriting logic semantics for probabilistic Event-B. The approach takes as input a probabilistic Event-B specification, and outputs a probabilistic rewrite theory that is fully executable in PMaude and can be statistically tested against quantitative metrics, using statistical model checking tools like MultiVeStA.
AOC 01/12/2022 Smoothed analysis of the simplex method, par Sophie Huiberts
Sophie Huiberts  
https://bbb.lipn.univ-paris13.fr/b/wol-ma9-vjn - code: 514019
01/12/2022    14:00 - 15:00
Résumé :
Explaining why the simplex method is fast in practice, despite it taking exponential time in the theoretical worst case, continues to be a challenge. Smoothed analysis is a paradigm for addressing this question. During my talk I will present an improved upper bound on the smoothed complexity of the simplex method, as well as prove the first non-trivial lower bound on the smoothed complexity. This is joint work with Yin Tat Lee and Xinzhi Zhang.
LOVE 01/12/2022 Directed homotopy type theory, par Paige Randall North
Paige Randall North, Utrecht University  
Salle B107, bâtiment B, Université de Villetaneuse
01/12/2022    10:30 - 12:00
Résumé :
In this talk, I will describe the development of a directed homotopy type theory. The aim is to capture (higher) categories and directed topological spaces as models of the theory, and thus use it to study phenomena such as concurrency and rewriting. I will explain homotopy type theory in a way that motivates this generalization, so prior knowledge of homotopy type theory is not required. I will also point out similarities between this work and modal approaches to linear type theory.
COMP 28/11/2022 Machine-Free Complexity 1, par Paulin de Naurois
Paulin de Naurois, CNRS, LIPN  
Hybride (Salle B107 et https://bbb.lipn.univ-paris13.fr/b/sei-nlh-8vr-xvy)
28/11/2022    14:30 - 15:30
Résumé :
LOVE 25/11/2022 Rewriting Logic Semantics and Symbolic Analysis for Parametric Timed Automata, par Laure Petrucci
Laure Petrucci, Équipe LoVe, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
25/11/2022    12:30 - 13:30
Résumé :
We present a rewriting logic semantics for parametric timed automata (PTAs) and shows that symbolic reachability analysis using Maude-with-SMT is sound and complete for the PTA reachability problem. We then refine standard Maude-with-SMT reachability analysis so that the analysis terminates when the symbolic state space of the PTA is finite. We show how we can synthesize parameters with our methods, and compare their performance with Imitator, a state-of-the-art tool for PTAs. The practical contributions are two-fold: providing new analysis methods for PTAs —e.g., allowing more general state properties in queries and supporting reachability analysis combined with user-defined execution strategies—not supported by Imitator, and developing symbolic analysis methods for real-time rewrite theories.
LOVE 25/11/2022 2-dimensional fixpoint operators, par Zeinab Galal
Zeinab Galal, University of Manchester  
Salle B107, bâtiment B, Université de Villetaneuse
25/11/2022    10:30 - 12:00
Résumé :
Fixpoint operators are tools to reason on recursive programs and infinite data types obtained by induction (e.g. lists, trees) or coinduction (e.g. streams). They were given a categorical treatment with the notion of categories with fixpoints. An important result by Plotkin and Simpson in this area states that provided some conditions on bifree algebras are satisfied, we obtain the existence of a unique uniform fixpoint operator. This theorem allows to recover the well-known examples of the category Cppo (complete pointed partial orders and continuous functions) in domain theory and the relational model in linear logic. In this talk, I will present a categorification of this result where the 2-dimensional framework allows to study the coherences associated to the reductions of ?-calculi with fixpoints i.e. the equations satisfied by the program computations steps.
AOC 24/11/2022 Combinatorial solvers and neural networks, par Pasquale Minervini
Pasquale Minervini  
https://bbb.lipn.univ-paris13.fr/b/wol-ma9-vjn - code: 514019
24/11/2022    10:30 - 11:30
Résumé :
Combining discrete probability distributions and combinatorial optimization problems with neural network components has numerous applications but poses several challenges. We propose Implicit Maximum Likelihood Estimation (IMLE), a framework for end-to-end learning of models combining discrete exponential family distributions and differentiable neural components. IMLE is widely applicable as it only requires the ability to compute the most probable states and does not rely on smooth relaxations. The framework encompasses several approaches such as perturbation-based implicit differentiation and recent methods to differentiate through black-box combinatorial solvers. Moreover, we show that IMLE simplifies to maximum likelihood estimation when used in some recently studied learning settings that involve combinatorial solvers. One limitation of IMLE is that, due to the finite difference approximation of the gradients, it can be especially sensitive to the choice of the finite difference step size which needs to be specified by the user. In this presentation, we also introduce Adaptive IMLE (AIMLE), the first adaptive gradient estimator for complex discrete distributions: it adaptively identifies the target distribution for IMLE by trading off the density of gradient information with the degree of bias in the gradient estimates. We empirically evaluate our estimator on synthetic examples, as well as on Learning to Explain, Discrete Variational Auto-Encoders, and Neural Relational Inference tasks. In our experiments, we show that our adaptive gradient estimator can produce faithful estimates while requiring orders of magnitude fewer samples than other gradient estimators.
COMP 21/11/2022 Kolmogorov complexity, par Ulysse Léchine
Ulysse Léchine, LIPN  
Hybride (Salle B107 et https://bbb.lipn.univ-paris13.fr/b/sei-nlh-8vr-xvy)
21/11/2022    14:30 - 15:30
Résumé :
LOVE 18/11/2022 strategFTO: Untimed control for timed opacity, par Dylan Marinho
Dylan Marinho, Université de Lorraine  
Salle B107, bâtiment B, Université de Villetaneuse
18/11/2022    12:30 - 13:30
Résumé :
We introduce a prototype tool strategFTO addressing the verification of a security property in critical software. We consider a recent definition of timed opacity where an attacker aims to deduce some secret while having access only to the total execution time. The system, here modeled by timed automata, is deemed opaque if for any execution time, there are either no corresponding runs, or both public and private corresponding runs. We focus on the untimed control problem: exhibiting a controller, i. e., a set of allowed actions, such that the system restricted to those actions is fully timed-opaque. We first show that this problem is not more complex than the full timed opacity problem, and then we propose an algorithm, implemented and evaluated in practice.
AOC 18/11/2022 On the solution of convex Semi-Infinite Problems, par Martina Cerulli
Martina Cerulli, Essec  
Amphi Copernic
18/11/2022    10:30 - 11:30
Résumé :
In this talk, we will present the results of the paper "Convergent algorithms for a class of convex semi-infinite programs" by M. Cerulli, A. Oustry, C. D'Ambrosio, L. Liberti, accepted for publication on SIAM Journal on Optimization. In this paper, we focus on convex Semi-Infinite Problems (SIPs) with an infinite number of quadratically parametrized constraints, not necessarily convex w.r.t. the parameter. A new convergent approach to solve these SIPs is proposed, leveraging the dualization of the inner problem. Indeed, based on the Lagrangian dual of the inner problem, a convex and tractable restriction of the considered SIP is derived. We state sufficient conditions for the optimality of this restriction. If these conditions are not met, the restriction is enlarged through an Inner-Outer Approximation Algorithm, and its value converges to the value of the original semi-infinite problem. This new algorithmic approach is compared with the classical Cutting Plane algorithm. We propose a new rate of convergence of the Cutting Plane algorithm, directly related to the iteration index, derived when the objective function is strongly convex, and under a strict feasibility assumption. We successfully test the two methods on two applications: the constrained quadratic regression and a zero-sum game with cubic payoff.
LOVE 15/11/2022 An Alternative (Multi-timed) Semantics for Modelling the Behaviour of Distributed Timed Systems, par James Ortiz
James Ortiz, Université de Namur  
Salle B107, bâtiment B, Université de Villetaneuse
15/11/2022    12:15 - 13:30
Résumé :
Distributed Timed Systems ( DTS) can be characterized by several communicating components whose behaviour depends on many timing constraints, and such component can be located at several computers spread over a communication network. Distributed Timed Automata ( DTA) and Timed Automata with Independent Clocks ( icTA) were introduced to model DTS. They are a variant of Timed Automata ( TA) with local clocks that may not run at the same rate. Model checking is a popular technique for automatic formal verification of untimed as well as timed systems. Unfortunately, this technique suffers from the well-known explosion problem: it becomes increasingly difficult to explore exhaustively the whole state space as the system grows, and this problem is exacerbated with the presence of clocks. To handle this problem, many techniques have emerged in recent years, among which bisimulation is popular. Timed bisimulation has already been proven to be decidable for TA. In this talk, I will show our alternative semantics (Multi-timed Automata ( MTA)), which is an extension of TA and icTA, whose execution traces can be modelled as sequences of pairs, where each pair contains an action and a tuple of timestamps. Thus, each action has its own tuple of the local time of occurrence for each component that belongs to the modelling DTS. Then, we have extended the theory of Timed Labelled Transition Systems ( TLTS) to Multi-Timed Labelled Transition Systems ( MLTS) and relate it through our alternative semantics for MTA. Also, we have revisited the notion of timed bisimulation on those automata, resulting in multi-timed bisimulation. We have proved its decidability and presented an EXPTIME algorithm for deciding whether two MTA are multi-timed bisimilar.
COMP 14/11/2022 Barriers in Complexity {II}, par Thomas Seiller
Thomas Seiller, CNRS, LIPN  
Hybrid (room B107 and https://bbb.lipn.univ-paris13.fr/b/sei-nlh-8vr-xvy)
14/11/2022    14:30 - 15:30
Résumé :
COMP 07/11/2022 A generic proof of the Cook-Levin theorem, par Paulin de Naurois
Paulin de Naurois, LIPN  
Hybride (salle B107 et https://bbb.lipn.univ-paris13.fr/b/sei-nlh-8vr-xvy)
07/11/2022    14:30 - 16:00
Résumé :
RCLN 07/11/2022 Trustworthy AI: Ethical considerations when using AI techniques, par Fernando Perez-Tellez
Fernando Perez-Tellez, TU Dublin  
Salle B107, bâtiment B, Université de Villetaneuse
07/11/2022    12:30 - 13:30
Résumé :
Recently, Artificial Intelligence (AI) is being used everywhere this is due to the accessibility of this technology in different aspects of everyday life. The idea of incorporating AI systems into several aspects of human life is to benefit humans by reducing labour and increasing everyday conveniences. Independently of the adopted definition of AI, we know that AI can either represent a benefit or an threat (unintentional in most of the cases). Then we should be thinking of creating intelligent systems considering important ethical and legal aspects. Dr. Fernando Perez Tellez, a lecturer and researcher from the Technological University Dublin (TU Dublin), Ireland is visiting LIPN. Dr. Perez Tellez will give a presentation on why is important to consider Ethics when AI techniques are used and how to make responsible use of AI. He will also present his TU Dublin colleagues research interests to promote the creation of potential research collaborations between LIPN and TU Dublin research groups.
COMP 24/10/2022 Algebraic complexity, par Christophe Tollu
Christophe Tollu, LIPN  
Hybride (salle B107 et https://bbb.lipn.univ-paris13.fr/b/sei-nlh-8vr-xvy)
24/10/2022    14:30 - 15:30
Résumé :
LOVE 24/10/2022 Modular Analysis of Tree-Topology Models, par Jaime Arias
Jaime Arias, Équipe LoVe, LIPN  
BBB : https://bbb.lipn.univ-paris13.fr/b/ari-uht-t3u
24/10/2022    12:15 - 13:30
Résumé :
Networks of automata that synchronise over shared actions are organised according to a graph synchronisation topology. In this topology, two automata are connected if they can jointly execute some action. We present a very effective reduction for networks with tree-like synchronisation topologies such that all automata after synchronising with their parents can execute only local (non-synchronising) actions: forever or until resetting, i.e. entering the initial state. We show that the reduction preserves reachability, but not liveness. This construction is extended to tree-like topologies of arbitrary automata and investigated experimentally.
COMP 17/10/2022 Boolean circuits, par Damiano Mazza
Damiano Mazza, CNRS, LIPN  
Hybride (salle E303 et https://bbb.lipn.univ-paris13.fr/b/sei-nlh-8vr-xvy)
17/10/2022    14:00 - 15:00
Résumé :
As part of the background lectures on complexity theory, this will cover the topic of Boolean circuits.
AOC 13/10/2022 Turn it around. The opportunities of Circular Economy in operation management, par Pablo Andres Maya
Pablo Andres Maya, Universidad de Antioquia Facultad de Medicina: Medellin, Antioquia, CO  
Salle B107, Université de Villetaneuse
13/10/2022    10:30 - 11:30
Résumé :
The traditional economic model based on produce, use, and disposal is reaching its limits. The Circular Economy is an alternative paradigm that envisions a better use of the limited resources we already have. However, putting into practice the circular economy imposes challenges and opportunities to operations management that are still to be addressed. We will discuss the role of analytics and operations research in tackling those challenges.
COMP 10/10/2022 Interactive proofs, par Ulysse Léchine
Ulysse Léchine, LIPN  
Hybride (salle B107 et https://bbb.lipn.univ-paris13.fr/b/sei-nlh-8vr-xvy)
10/10/2022    14:30 - 15:30
Résumé :
As part of the background lectures on complexity theory, this will cover the topic of interactive proofs.
COMP 03/10/2022 Barriers in Complexity {I}, par Thomas Seiller
Thomas Seiller, CNRS, LIPN  
Séminaire Hybride: Salle B107 (LIPN) et https://bbb.lipn.univ-paris13.fr/b/sei-nlh-8vr-xvy
03/10/2022    14:30 - 15:30
Résumé :
This is the first of a series of two-to-three lectures on barriers in computational complexity, i.e. negative results showing that (some) proof techniques are inefficient against (some) open problems in the field.
LOVE 15/09/2022 The (infinity,1)-category of Types, par Eric Finster
Eric Finster, University of Birmingham  
Salle B107, bâtiment B, Université de Villetaneuse and online
15/09/2022    10:30 - 11:30
Résumé :
A major outstanding difficulty in Homotopy Type Theory is the description of coherent higher algebraic structures. As an example, we know that the algebraic structure possessed by the collection of types and functions between them is *not* a traditional 1-category, but rather an (infinity,1)-category. In this talk, I will describe how the addition of a finite collection additional definitional equalities designed to render the notion of "opetopic type" definable in fact allows one to construct the (?,1)-category structure on the universe of types.
LOVE 16/06/2022 Parallelism in Soft Linear Logic, par Paulin Jacobé de Naurois
Paulin Jacobé de Naurois, CNRS, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
16/06/2022    10:30 - 11:30
Résumé :
We extend the Soft Linear Logic of Lafont with a new kind of modality, called parallel. Contractions on parallel modalities are only allowed in the cut and the left -o rules, in a controlled, uniformly distributive way. We show that SLL, extended with this parallel modality, is sound and complete for PSPACE. We propose a corresponding typing discipline for the lambda-calculus, extending the STA typing system of Gaboardi and Ronchi, and establish its PSPACE soundness and completeness. The use of the parallel modality in the cut-rule drives a polynomial-time, parallel call-by-value evaluation strategy of the terms.
LOVE 09/06/2022 Bunched Fuzz: Sensitivity for Vector Metrics, par Patrick Baillot
Patrick Baillot, CNRS, Cristal, Lille  
Salle B107, bâtiment B, Université de Villetaneuse
09/06/2022    10:30 - 11:30
Résumé :
"Program sensitivity" measures the distance between the outputs of a program when it is run on two related inputs. This notion, which plays an important role in areas such as differential privacy and optimization, has been the focus of several program analysis techniques introduced in recent years. One approach that has proved particularly fruitful for this domain is the use of type systems inspired by linear logic, as pioneered by Reed and Pierce in the Fuzz programming language. In Fuzz, each type is equipped with its own notion of distance, and the typing rules explain how those distances can be treated soundly when analyzing the sensitivity of a program. In particular, Fuzz features two products types, corresponding to two different sensitivity analyses: the "tensor product" combines the distances of each component by adding them, while the "with product" takes their maximum. In this talk we will show how products in Fuzz can be generalized to arbitrary Lp distances, metrics that are often used in privacy and optimization. The original Fuzz products, tensor and with, correspond to the special cases L1 and L?. To handle the generalized products, we extend the Fuzz type system with bunches -- as in the logic of bunched implications -- where the distances of different groups of variables can be combined using different Lp distances. We show that our extension, Bunched Fuzz, can be used to reason about important examples of metrics between probability distributions in a natural way. This is joint work with june wunder, Arthur Azevedo de Amorim, and Marco Gaboardi.
AOC 02/06/2022 On two two-level problems for operational warehouse planning in person-to-parts order picking systems, par Stefan Irnich
Stefan Irnich, Gutenberg School of Management and Economics, Chair of Logistics Management - Université de Mainz  
Visio - https://bbb.lipn.univ-paris13.fr/b/wol-ma9-vjn -code 514019
02/06/2022    11:45 - 12:45
Résumé :
We present a new modeling and solution approach for two-level problems in warehousing where one level concerns picking operations in a manual picker-to-parts warehouse. In particular, we consider the single picker routing problem with scattered storage (SPRP-SS) and the joint order batching and picker routing problem (JOBPRP). The SPRP-SS assumes that an article is, in general, stored at more than one pick position. The task is then the simultaneous selection of pick positions for requested articles and the determination of a minimum-length picker tour collecting the articles. In the JOBPRP, a set of orders is given, each with one or several order lines requesting a number of articles. The problem is here to group the given orders into capacity-feasible batches so that the total length of the picker tours collecting the respective articles is minimized. It is a classical result of Ratliff and Rosenthal that, for given pick positions, an optimal picker tour is a shortest path in the state space of a dynamic program with a linear number of states and transitions. We extend the state space of Ratliff and Rosenthal so that every feasible picker tour is still a path. Furthermore, the additional requirement to make consistent selections and grouping decisions can be modeled as additional constraints in shortest-path problems. We propose to solve these problems with a MIP solver. We will explain why this approach is not only convenient and elegant but also generic: it covers optimal solutions to integrated problems that use heuristic routing policies for the picker tours, consider different warehouse layouts, and incorporate further extensions. Computational experiments with a direct MIP solver-based approach for the SPRP-SS and a branch-price-and-cut algorithm for the JOBPRP show that the new modeling and solution approach outperforms the available exact algorithms. The latter computes hundreds of new best and provably optimal solutions to open instances of three JOBPRP benchmark sets. (joint work with Katrin Heßler)
LOVE 19/05/2022 Fully abstract translation for parametric polymorphism to dynamic sealing via game semantics, par Guilhem Jaber
Guilhem Jaber, Université de Nantes  
Salle B107, bâtiment B, Université de Villetaneuse
19/05/2022    10:30 - 11:30
Résumé :
In this talk, we will present trace models for typed higher-order effectful programming languages, including System F, and the cryptographic lambda-calculus, a language with an idealised model of encryption. Our models are defined by representing programs as labeled transition systems generating all possible interactions with the environment, following operational presentation of game semantics. In a setting with mutable store, we provide a proof of full-abstraction, that is equality in the model corresponds to contextual equivalence of the programming language. From these models, we derive a general methodology to build fully-abstract compilation schemes. We apply it to derive the first fully abstract compilation scheme from System F, to the cryptographic lambda-calculus, in presence of mutable store. This compilation scheme can be seen as a refinement of the one proposed by Sumii and Pierce, that was shown to not be fully-abstract by Devriese, Patrignani and Piessens.
LOVE 12/05/2022 Groupoidal Realizability, par Sam Speight
Sam Speight, University of Oxford  
Salle B107, bâtiment B, Université de Villetaneuse
12/05/2022    10:30 - 11:30
Résumé :
I will describe ongoing work attempting to rethink categorical realizability models of type theory in the context of intensional and homotopy type theory. The idea is to equip the Hofmann-Streicher groupoid model of type theory with a notion of realizability analogous to how traditional categories of assemblies do so for the set model. Realizers derive from a "realizer category" that is assumed to have increasingly more structure as we seek to model a more expressive type theory. The key ingredient is an interval qua co-groupoid internal to the realizer category, facilitating a definition of homotopy and an abstract fundamental groupoid construction. Objects in a groupoid are realized by points in some fundamental groupoid; isomorphisms are realized by paths. Insofar as realizability interpretations are said to formalize the (informal) BHK interpretation, we claim that groupoidal realizability formalizes the informal homotopy interpretation of intensional type theory, or the "topological BHK interpretation". I will show how impredicative and univalent universes can be modelled via the relationship between "modest groupoids" and "generalized congruences", and, time permitting, will discuss how this work makes contact with some classical topics in theoretical computer science, such as domain theory and game semantics.
AOC 21/04/2022 Fast algorithms for some parametric optimization problems, par Hassan Aissi
Hassan Aissi, LAMSADE - Paris Dauphine  
Salle B107, bâtiment B, Université de Villetaneuse
21/04/2022    10:30 - 11:30
Résumé :
Parametric optimization is a rich field with applications ranging from sensitivity analysis, Lagrangian relaxation, multiobjective optimization, and minimum-ratio optimization. We consider in this talk some parametric problems related to the minimum cut, in which we are given a graph G=(V,E) with edge costs that are affine functions of a parameter ???d. We develop strongly polynomial algorithms for these problems that are faster than known techniques.
AOC 07/04/2022 Quantum Computing for Process Systems Engineering, par David Bernal Neira
David Bernal Neira, Associate scientist in quantum computing at the Research Institute of Advanced Computer Science (RIACS) of the Universities Space Research Association (USRA) and QuAIL at NASA  
Salle B107, bâtiment B, Université de Villetaneuse
07/04/2022    11:30 - 12:30
Résumé :
Optimization problems arise in different areas of Process Systems Engineering (PSE), and solving these problems efficiently is essential for addressing important industrial applications. Quantum computers have the potential to efficiently solve challenging nonlinear and combinatorial problems. However, available quantum computers cannot solve practical problems; they are limited to small sizes and do not handle constraints well. In this talk, we propose hybrid classical-quantum algorithms to solve mixed-integer nonlinear problems (MINLP) and apply decomposition strategies to break down MINLPs into Quadratic Unconstrained Binary Optimization (QUBO) subproblems that can be solved by quantum computers. We will also cover different approaches to solving Quadratic Unconstrained Binary Optimization (QUBO) problems through unconventional computation methods, including but not limited to Quantum algorithms, and discuss how these approaches lead to algorithms able to outperform classical solution approaches
RCLN 28/03/2022 Abstractive Summarization Evaluation: Overview and Reflections, par Yanzhu Guo
Yanzhu Guo, LIX - Ecole Polytechnique  
Salle B107, bâtiment B, Université de Villetaneuse
28/03/2022    13:00 - 14:30
Résumé :
The topic of summarization evaluation has recently received a surge of attention due to the rapid development of abstractive summarization systems. We conduct a survey of the state-of-the-art evaluation metrics along with relevant datasets and visualization systems. We also touch upon the statistical deficiencies in current meta-evaluation approaches such as the problematic choice of scoring range, the lack of paired evaluation as well as the prevalence of underpowered tests. Finally, we show experimental results proving the unreliability of human-annotated ground-truth reference summaries and thus argue for reference-free metrics as a more promising future direction.
AOC 17/03/2022 A Tailored Benders Decomposition Approach for Last-mile Delivery with Autonomous Robots, par Ivana Ljubic
Ivana Ljubic, ESSEC  
Salle B107, bâtiment B, Université de Villetaneuse
17/03/2022    12:30 - 13:30
Résumé :
This work addresses an operational problem of a logistics service provider that consists of finding an optimal route for a vehicle carrying customer parcels from a central depot to selected facilities, from where autonomous devices like robots are launched to perform last-mile deliveries. The objective is to minimize a tardiness indicator based on the customer delivery deadlines. We provide a better understanding of how three major tardiness indicators can be used to improve the quality of service by minimizing the maximum tardiness, the total tardiness, or the number of late deliveries. We study the problem complexity, devise a unifying Mixed Integer Programming formulation and propose an efficient branch-and-Benders-cut scheme to deal with instances of realistic size. Numerical results show that this novel Benders approach with a tailored combinatorial algorithm for generating Benders cuts largely outperforms all other alternatives. In our managerial study, we vary the number of available facilities, the coverage radius of autonomous robots and their speed, to assess their impact on the quality of service and environmental costs. Joint work with: L. Alfandari and M.M. de Silva
LOVE 11/03/2022 Lightweight (yet efficient) verification of cyber-physical systems, par Étienne André
Étienne André, LORIA  
Salle B107, bâtiment B, Université de Villetaneuse
11/03/2022    11:15 - 12:15
Résumé :
Monitoring of cyber-physical systems attracts both scientific and practical attention. However, monitoring algorithms suffer from the methodological difficulty of only observing sampled discrete-time signals, while real behaviors are continuous-time signals. To mitigate this problem of sampling uncertainties, we introduce a model-bounded monitoring scheme, where we use prior knowledge about the target system to prune interpolation candidates. Technically, we express such prior knowledge by linear hybrid automata (LHAs)---the LHAs are called bounding models. We present two partial algorithms---one is via reduction to reachability in LHAs and the other is a direct one using polyhedra---and show that these methods, and thus the proposed model-bounded monitoring scheme, are efficient and practically relevant. This presentation is based on joint works with Ichiro Hasuo and Masaki Waga.
LOVE 20/01/2022 Functional interpretations and applications, par [Chocola] Bruno Dinis
[Chocola] Bruno Dinis, Universidade de Lisboa, Portugal  
https://chocola.ens-lyon.fr/events/meeting-2022-01-20/
20/01/2022    10:00 - 12:00
Résumé :
Functional interpretations are maps of formulas from the language of one theory into the language of another theory, in such a way that provability is preserved. These interpretations typically replace logical relations by functional relations. Functional interpretations have many uses, such as relative consistency results, conservation results, and extraction of computational content from proofs as is the case in the so-called proof mining program. I will present several recent functional interpretations and some results that come from these interpretations. I will also give examples of application of functional interpretations, in the spirit of the proof mining program.
LOVE 13/01/2022 Extended Addressing Machines for PCF, with Explicit Substitutions, par Nicolas Munnich
Nicolas Munnich, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse (retransmis sur BBB: https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (code d'accès 749983))
13/01/2022    10:30 - 11:30
Résumé :
Addressing machines have been introduced as a formalism to construct models of the pure, untyped lambda-calculus. We extend the syntax of their programs by adding instructions for executing arithmetic operations on natural numbers, and introduce a reflection principle allowing certain machines to access their own address and perform recursive calls. We prove that the resulting extended addressing machines naturally model a weak call-by-name PCF with explicit substitutions. Finally, we show that they are also well suited for representing regular PCF programs (closed terms) computing natural numbers.
LOVE 06/01/2022 Bayesian Networks and Proof-Nets, par Claudia Faggian
Claudia Faggian, IRIF, CNRS & Université de Paris  
En ligne: https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (code d'accès 749983)
06/01/2022    10:30 - 11:30
Résumé :
(Joint work with Thomas Ehrhard and Michele Pagani) Bayesian networks are a powerful tool for probabilistic reasoning. They allow for a compact representation of large probability distributions, and for efficient inference algorithms. A Bayesian Network consists of two parts: a qualitative component in the form of a directed acyclic graph (DAG), and a quantitative component, in the form conditional probabilities. Strikingly, linear logic proof-nets have a similar nature: a graph structure represents the proof, a quantitative interpretation yields the semantics. In this talk, we present recent (and on-going) work to explore the connection between Bayesian Networks and (Multiplicative) Proof-Nets, uncovering a strong correspondence between the two structures, and their quantitative interpretation.
LOVE 09/12/2021 Refining vector spaces using norms, par Nicolas Blanco
Nicolas Blanco, University of Birmingham  
Salle B107, bâtiment B, Université de Villetaneuse (retransmis sur BBB)
09/12/2021    10:30 - 11:30
Résumé :
In this talk, I will introduce the theory of bifibrations of polycategories and its relation to refinement types and classical multiplicative linear logic. I will illustrate this on an example, where norms are seen as refining vector spaces. I will explain how to recover the norms for interpreting the connectives of MLL using this perspective. I will also show how it shed light on some other properties of these norms. I will conclude by mentioning some possible extensions of this work.
LOVE 02/12/2021 Journée-Séminaire Chocola
 
ENS Lyon
02/12/2021    09:30 - 17:00
Résumé :
LOVE 29/11/2021 Guaranteed properties of dynamical systems under perturbations, par Jawher Jerray
Jawher Jerray, LIPN, Équipe LoVe  
Salle B107, bâtiment B, Université de Villetaneuse
29/11/2021    12:00 - 13:00
Résumé :
ince dynamical systems has a major impact on human development, especially critical systems that can put human lives at risk if something goes wrong. Hence, the need of studying the behavior of these systems in order to guarantee their correct functioning. Nevertheless, computing such type of system has never been an easy task, as the complexity of these systems is constantly increasing, in addition to the perturbations that may arise during their performance, as well as undefined parameters that may exist. To ensure that a system always produces the expected results and does not fail in any way, a formal verification of its behavior and properties is necessary. In this work, we study dynamical systems from different aspects and using various techniques. More specifically, we focus on the formal verification of some of its critical properties such as schedulability, synchronization, robustness and stability. In the first part, we study the schedulability of the flight control of a space launcher with unknown parameters and under constraints. Then, we propose a synthesis of the admissible timing values of the unknown parameters by a parametric timed model checker. We increase the complexity of the problem by taking into consideration the switch time between two threads. We extend this work by developing a tool that translates a given real-time system design into parametric timed automata in order to infer some timing constraints ensuring schedulability. In the second part, we study the stability of dynamical systems and the robustness of controls. We give a simple technique based on Euler's integration method which allows to build an invariant set around a given system. This technique guarantees that the approximate Euler solutions are attracted by a limit cycle. We apply the method on different systems, including chaotic systems with strange attractors. Furthermore, we show that a basic combination of a random sampling with a symbolic computation method assists to deal with robust control problems for nonlinear systems. Also, we illustrate a basic condition guaranteeing that a system with perturbation is robust under a repeated control sequence obtained by solving a horizon optimal control problem. Finally, we unified the main contributions of the second part in a tool called ORBITADOR which checks the stability of a given system and notably returns plots containing the evolution of the system in different views and the shape of the invariant if it exists.
LOVE 29/11/2021 A General Framework for Supervision of Opacity, par Nour SOUID
Nour SOUID, LIPN, Équipe LoVe  
Salle B107, bâtiment B, Université de Villetaneuse
29/11/2021    11:00 - 12:00
Résumé :
Opacity is a property of information flow that characterizes the ability of a system to keep an information secret from a third party called an attacker. In this paper, we investigate the problem of reinforcing the opacity using the Supervisory Control Theory. We present a novel approach to synthesize a supervisor to the system that prevents, at run time, a malicious observer from deducing secret information. Our approach is general since it does not take into consideration the relationship between the attacker's observation and the supervisor's one. Moreover, being based on formal methods, it allows us to represent various systems in different contexts. Particularly, we focus on web services and we apply our approach to a B2B (business-to-business) e-commerce use case.
AOC 25/11/2021 SMS++: a Structured Modelling System with ... hopefully, one day ... some useful application?, par Antonio Frangioni
Antonio Frangioni, Università di Pisa  
Salle B107, bâtiment B, Université de Villetaneuse
25/11/2021    10:30 - 11:30
Résumé :
On February this year, after about 8 years of gestation, an early beta release of the Structured Modelling System++ has been released to general public availability. SMS++ is a C++ library intended to facilitate the development of very large optimization problems with multiple nested heterogeneous structure, and especially of the corresponding solution methods, chiefly (but not exclusively) ones based on (parallel) decomposition. In the attempt of achieving this goal SMS++ has accrued a number of features that look quite unique in the landscape of modelling systems, so much so as to raise the legitimate suspicion that the reason why these features have never been developed before is because no sane person would have ever thought them a good idea. Yet the system is there and it does seem to offer some new viewpoints on mathematical modelling systems that may at least be worth a look. SMS++ is itself developed in an highly modular fashion and already counts a(n hopefully growing) number of separate sub-projects besides the "core" library and the support tools. One of these allows to solve Lagrangian Duals of complex integer programs with remarkable ease, and it will hopefully soon be joined by a similar component doing Benders' decomposition. Hence, there may actually be a few use cases in which SMS++ could be worth considering already, despite the very many missing components that would be needed to make it a really compelling prposition. In fact, perhaps the most interesting feature of SMS++ is it being community-oriented and (at least in principle) almost infinitely extendable to try to cater for the very diverse needs of the disparate clades of the optimization world. This alone may make it worth a second look, notwithstanding the arguably insane delusions of an all-conquering modelling system that some of the developers harbour and that would require capturing an unfeasibly large amount of mindshare to achieve.
LOVE 25/11/2021 Superpolynomial Lower Bounds Against Low-Depth Algebraic Circuits, par Nutan Limaye, Srikanth Srinivasan, Sebastien Tavenas
Nutan Limaye, Srikanth Srinivasan, Sebastien Tavenas, ITU Copenhagen, Aarhus University, CNRS & Université Savoie-Mont-Blanc  
Salle B107, bâtiment B, Université de Villetaneuse -- retransmis sur https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (code d'accès 749983)
25/11/2021    10:00 - 11:00
Résumé :
An Algebraic Circuit for a polynomial PF[x1xN] is a computational model for constructing the polynomial P using only additions and multiplications. It is a syntactic model of computation, as opposed to the Boolean Circuit model, and hence lower bounds for this model are widely expected to be easier to prove than lower bounds for Boolean circuits. Despite this, we do not have superpolynomial lower bounds against general algebraic circuits of depth 3 (except over constant-sized finite fields) and depth 4 (over fields other than F2), while constant-depth Boolean circuit lower bounds have been known since the early 1980s. In this paper, we prove the first superpolynomial lower bounds against general algebraic circuits of all constant depths over all fields of characteristic 0 (or large). We also prove the first lower bounds against homogeneous algebraic circuits of constant depth over any field. Our approach is surprisingly simple. We first prove superpolynomial lower bounds for constant-depth Set-Multilinear circuits. While strong lower bounds were already known against such circuits, most previous lower bounds were of the form f(d)poly(N), where d denotes the degree of the polynomial. In analogy with Parameterized complexity, we call this an FPT lower bound. We extend a well-known technique of Nisan and Wigderson (FOCS 1995) to prove non-FPT lower bounds against constant-depth set-multilinear circuits computing the Iterated Matrix Multiplication polynomial IMMnd (which computes a fixed entry of the product of d nn matrices). More precisely, we prove that any set-multilinear circuit of depth computing IMMnd must have size at least ndexp(?O()) This result holds over any field, as long as d=o(logn). We then show how to convert any constant-depth algebraic circuit of size s to a constant-depth set-multilinear circuit with a blow-up in size that is exponential in d but only polynomial in s over fields of characteristic 0. (For depths greater than 3, previous results of this form increased the depth of the resulting circuit to (logs).) This implies our constant-depth circuit lower bounds. We can also use these lower bounds to prove a Depth Hierarchy theorem for constant depth circuits. We show that for every depth , there is an explicit polynomial which can be computed by a depth circuit of size s, but requires circuits of size s(1) if the depth is ?1. Finally, we observe that our superpolynomial lower bound for constant-depth circuits implies the first deterministic sub-exponential time algorithm for solving the Polynomial Identity Testing (PIT) problem for all small depth circuits using the known connection between algebraic hardness and randomness.
LOVE 22/11/2021 Can a single transition stop an entire Petri net?, par Prof. Dr. Jörg Desel
Prof. Dr. Jörg Desel, FernUniversität in Hagen  
Salle B107, bâtiment B, Université de Villetaneuse
22/11/2021    13:00 - 14:00
Résumé :
A transition stops a Petri net if, from any reachable marking, each occurrence sequence without this transition is finite. For bounded Petri nets it is easy to decide if a transition stops a net. We show that the coverability graph can be used to decide the property for unbounded Petri nets. A corresponding tool considers moreover generalisations of the above property.
LOVE 18/11/2021 Implementing the mwp-flow analysis, par Neea Rusch
Neea Rusch, University of Augusta  
Salle B107, bâtiment B, Université de Villetaneuse (retransmis sur https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24; code d'accès 749983)
18/11/2021    10:30 - 11:30
Résumé :
Jones and KristiansenÂ’s mwp-flow analysis certifies polynomial bounds on the size of the values returned by an imperative program. This method is compositional, extensible and elegant, as it bounds transitions between states instead of focusing on states in isolation. While simple to use, this theoretical result is difficult to prove correct and implement. Here we detail the challenges a naive implementation has to face, and how we remedied them to offer a fast, efficient and extended implementation of the technique. The result, pymwp, is a lightweight tool to automatically perform data-size analysis of C programs. This effort prepares and enables the development of certified complexity analysis, by transforming a costly analysis into a tractable program, that leverages compositionality and decorrelates the problem of finding the existence of a bound with its value.
AOC 18/11/2021 Optimization + Simulation: how to reduce bus bunching, par Yasmin A Rios Solis
Yasmin A Rios Solis, Escuela de Ingeniería y Ciencias - Campus Monterrey - Tecnológico de Monterrey, México  
ATTENTION Salle D215, bâtiment D, Université de Villetaneuse
18/11/2021    10:30 - 11:30
Résumé :
Real-time control strategies palliate with the day's dynamics in bus rapid transit systems. In this talk, we focus on a bus bunching problem that minimizes the number of buses of the same line cruising head-to-tail or arriving at a stop simultaneously by using bus holding times at the stops. For this, we propose a new mathematical model with quadratic constraints, whose objective function minimizes the penalties caused by buses that are bunching. Experimental results on a simulation of a bus rapid transit system in Monterrey, Mexico, show the efficiency of our approach. The results show a bus bunching reduction of 45% compared to the case without optimization. Moreover, in some scenarios the passenger waiting times are reduced by 30%.
LOVE 15/11/2021 Model Checking of Solidity Smart Contracts Adopted For Business Processes, par Ikram Garfatta
Ikram Garfatta, LIPN, Équipe LoVe  
Salle B107, bâtiment B, Université de Villetaneuse
15/11/2021    14:00 - 15:00
Résumé :
Several features of the Blockchain technology are well aligned with critical issues in the Business Process Management (BPM) field, and yet adopting Blockchain for BPM should not be taken lightly. In fact, the security of smart contracts, which are one of the main elements of the Blockchain that make the integration with BPM possible, has proved to be vulnerable. It is therefore crucial for the protection of the designed business processes to prove the correctness of the smart contracts to be deployed on a blockchain. In this talk, I will present our formal approach based on the transformation of Solidity smart contracts, with consideration of the BPM context in which they are used, into a Hierarchical Coloured Petri net. We express a set of smart contract vulnerabilities as temporal logic formulae and use the Helena model checker to, not only detect such vulnerabilities while discerning their exploitability, but also check other temporal-based contract-specific properties.
LOVE 15/11/2021 A Smart Software System for Fire Risk Notification, par Prof. Lars Michael Kristensen
Prof. Lars Michael Kristensen, Software Engineering Research Group - Western Norway University of Applied Sciences  
Salle B107, bâtiment B, Université de Villetaneuse
15/11/2021    13:00 - 14:00
Résumé :
Cold winter seasons result in very dry indoor conditions and have historically led to severe fires in the high and dense representation of wooden homes in Norway. To reduce fire conflagration probability and consequences, it is necessary to have an accurate estimate of the current and near future fire risk to take proper planning precautions. The DYNAMIC research project supported by the Norwegian Research Council has two main objectives: 1) to develop (mathematical) fire risk models that are able to quantify fire risk; 2) to investigate how cloud computing services providing access to weather data can be combined with recent developments in fire risk modelling to enable smart and fine-grained fire risk prediction services. The first part of the talk presents results from a first prototype implementation of a microservice-based fire risk notification system that has been experimentally validated at selected geographical locations in Norway. The system relies on weather data provided by cloud services of the Norwegian Meteorological Institute. Our experimental evaluation demonstrates the ability to provide trustworthy and accurate fire risk indications using a combination of recorded weather data and forecasts. Furthermore, our cloud- and micro-service software system implementation is efficient with respect to data storage and computation time. The second part of the talk presents work-in-progress on formal modelling and behavioural validation of the software architecture for the fire risk notification system.
RCLN 12/11/2021 Relation Extraction with Distant Supervision: noise Reductio, par Juan Luis Garcia-Mendoza
Juan Luis Garcia-Mendoza, Laboratorio de Tecnologias del Lenguaje, INAOE Puebla  
Salle B107, bâtiment B, Université de Villetaneuse
12/11/2021    12:30 - 13:45
Résumé :
Distant Supervision is an approach that allows automatic labeling of instances. This approach has been used in Relation Extraction. Still, the main challenge of this task is handling instances with noisy labels (e.g., when two entities in a sentence are automatically labeled with an invalid relation). The approaches reported in the literature addressed this problem by employing noise-tolerant classifiers. However, if a noise reduction stage is introduced before the classification step, this increases the macro precision values or keep the same values with fewer instances. An approach based on Adversarial Autoencoders is proposed to obtain a new representation that allows noise reduction in Distant Supervision.
LOVE 28/10/2021 Variable binding and substitution for (nameless) dummies, par Ambroise Lafont
Ambroise Lafont, University of Sydney  
Salle B107, bâtiment B, Université de Villetaneuse -- retransmis sur https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (code d'accès 749983)
28/10/2021    10:30 - 11:30
Résumé :
By abstracting over well-known properties of De Bruijn's representation with nameless dummies, we design a new theory of syntax with variable binding and capture-avoiding substitution. We propose it as a simpler alternative to Fiore, Plotkin, and Turi's approach, with which we establish a strong formal link. We also show that our theory easily incorporates simple types and equations between terms. Joint work with Tom & Andre Hirschowitz, Marco Maggesi
LOVE 21/10/2021 [Séminaire Chocola] Program verification on a capability machine in the presence of untrusted code, par Armaël Guéneau
Armaël Guéneau, University of Aarhus  
https://chocola.ens-lyon.fr/events/online-2021-10-22/
21/10/2021    10:00 - 12:00
Résumé :
A capability machine is a kind of CPU with hardware support for fine-grained privilege separation. Practical designs and prototypes for such machines are seeing recent development as part of the CHERI project (University of Cambridge, SRI, ARM) (cheri-cpu.org, morello-project.org), making capability machines a promising target for designing and building new software with security in mind. In this talk, I will present some of the work done at Aarhus University and KU Leuven on developing formal principles for reasoning about security properties of code running on capability machines. I will show how one can prove functional correctness of programs that interact with untrusted (and possibly malicious) code while leveraging capabilities to protect their private state. The key aspects of this methodology are a program logic for reasoning about known code, and a logical relation providing a /universal contract/ of unknown code. The whole work has been mechanized in Coq using the Iris framework.
AOC 14/10/2021 Incorporating Holding Costs in Continuous-Time Service Network Design: New Model, Relaxation and Exact Algorithm, par Roberto Baldacci
Roberto Baldacci, Department of Electrical, Electronic, and Information Engineering “Guglielmo Marconi”, University of Bologna, Italy  
ATTENTION : Salle C311, bâtiment C, Université de Villetaneuse
14/10/2021    10:30 - 11:30
Résumé :
The continuous-time service network design problem (CTSNDP) occurs widely in practice. It aims to minimize the total operational cost by optimizing schedules of transportation services and routes of shipments for dispatching, which can occur at any time point along a continuous planning horizon. In order to be cost effective, shipments often wait to be consolidated, which incurs holding cost. Despite its importance, the holding cost has not been taken into account in the existing studies on the CTSNDP, since introducing it will significantly complicate the problem and make the solution development very challenging. To tackle this challenge, we develop a new dynamic discretization discovery algorithm, which can solve the CTSNDP with holding cost to exact optimum. The algorithm is based on a novel relaxation model and several new optimization techniques. Results from extensive computational experiments validate the efficiency and effectiveness of the new algorithm, as well as demonstrating the benefits that can be gained by taking into account holding costs in solving the CTSNDP. In particular, we show that the significance of the benefits depends on the connectivity of the underline physical network and the flexibility of the shipmentsÂ’ time requirements.
LOVE 14/10/2021 Logique(s) linéaire(s) indexée(s) : syntaxe, structure et sémantique du fragment multiplicatif-additif, par Flavien Breuvart
Flavien Breuvart, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse -- retransmis sur https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (code d'accès 749983)
14/10/2021    10:30 - 11:30
Résumé :
Nous allons décrire la logique linéaire indexée introduite par T.Ehrhard et A.Bucciarelli il y a 20 ans, expliquer en quoi cette logique est à la fois similaire à d'autres mais avec des particularités uniques. En particuliers nous verrons ses liens avec les logiques BLL-like avec aussi des exponentielles indexées. Dans un troisième temps nous expliquerons comment généraliser l'un et l'autre pour y greffer une notion abstraite de structure de ressources. Enfin, et selon les désir de l’audience, nous allons traiter l'aspect sémantique (catégorique et/or dénotationnel) du fragment additif de ces généralisation.
LOVE 30/09/2021 Call-by-Value, Again!, par Axel Kerinec
Axel Kerinec, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse -- retransmis sur https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (code d'accès 749983)
30/09/2021    10:30 - 11:30
Résumé :
The quest for a fully abstract model of the call-by-value ?-calculus remains crucial in programming language theory, and constitutes an ongoing line of research. While a model enjoying this property has not been found yet, this interesting problem acts as a powerful motivation for investigating classes of models, studying the associated theories and capturing operational properties semantically. In this presentation we study a relational model presented as a relevant intersection type system, where intersection is in general non-idempotent, except for an idempotent element that is injected in the system. This model is adequate, equates many ?-terms that are indeed equivalent in the maximal observational theory, and satisfies an Approximation Theorem w.r.t. a system of approximants representing finite pieces of call-by-value Böhm trees. We show that these tools can be used for characterizing the most significant properties of the calculus – especially solvability. We also prove the decidability of the inhabitation problem for our type system. This is joint work with Simona Ronchi Della Rocca and Giulio Manzonetto, published at FSCD 2021.
AOC 23/09/2021 Design of diversified package tours for the digital travel industry : A branch-cut-and-price approach , par Laurent Alfandari
Laurent Alfandari, ESSEC  
Salle B107, bâtiment B, Université de Villetaneuse
23/09/2021    10:30 - 11:30
Résumé :
Motivated by the revolution brought by the internet and communication technology in daily life, this paper examines how the online travel agencies (OTA) can use these technologies to improve customer value. We consider the design of a fixed number of package tours offered to customers in the digital travel industry. This can be formulated as a Team Orienteering Problem (TOP) with restrictions on budget and time. Different from the classical TOP, our work is the first one to introduce controlled diversity between tours. This enables the OTA to offer tourists a diversified portfolio of tour packages for a given period of time, each potential customer choosing a single tour in the selected set, rather than multiple independent tours over several periods as in the classical TOP. Tuning the similarity parameter between tours enables to manage the trade-off between individual preferences in consumersÂ’ choices and economies of scale in agenciesÂ’ bargaining power. We propose compact and extended formulations and solve the master problem by a branch-and-price method, and an alternative branch-cut-and-price method. The latter uses a delayed dominance rule in the shortest path pricing problem solved by dynamic programming. A particularity of the model is that in the column generation phase, the diversity constraints hold between each pair of columns, which is unusual and requires to generate these constraints on the fly. Our methods are tested over benchmark TOP instances of the literature, and a real dataset collected from a Chinese OTA. We explore the impact of tours diversity on all stakeholders, and assess the computational performance of the various approaches.
LOVE 16/09/2021 Physic-agnostic computational models, par Titouan Carette
Titouan Carette, LORIA & LRI  
Salle B107, bâtiment B, Université de Villetaneuse -- retransmis sur https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (code d'accès 749983)
16/09/2021    10:30 - 11:30
Résumé :
Here is a (not so...) secret recipe to write a lot of papers: take any computational concept you like and add quantum, probabilistic, reversible, etc... before the name. In practice this is however not so easy, it often requires to start from scratch to find a formulation fitting our specific framework. Another way is to formulate the computational concept in an abstract language that can then be instantiated to the physical theory we have in mind. This can be done using category theory. An abstract computational process is represented by a string diagram and then interpretation functors provide semantics in various physical models. In this talk I will provide an example of such physic-agnostic model in the form of a diagrammatic approach to quantum streams. We will see that once we have designed the abstract graphical model, varying the physical theory can lead to interesting computational but also physical considerations.
LOVE 01/07/2021 [Séminaire Chocola] Milner and Alur walk into a bar, par Daniele Varacca
Daniele Varacca, LACL - Univ Paris Est Creteil  
https://chocola.ens-lyon.fr/events/online-2021-07-01/
01/07/2021    10:00 - 12:00
Résumé :
The chef kicks them out: "I'm sorry, in my kitchen we only use induction". This talk will start from Morris' PhD thesis in 1968 and present 50 years of theoretical computer science, through PCF, CCS, Alternating transition systems, contexts and strategies, ending up at the footsteps of the monumental Palace of Justice in Créteil.
LOVE 29/06/2021 Fault-tolerant LU factorization is low cost, par Daniel Torres Gonzalez
Daniel Torres Gonzalez, LIPN  
https://bbb.lipn.univ-paris13.fr/b/ari-uht-t3u
29/06/2021    15:00 - 16:00
Résumé :
At large scale, failures are statistically frequent and need to be taken into account. Tolerating failures has arisen as a major challenge in parallel computing as the size of the systems grow, failures become more common and some computation units are expected to fail during the execution of a program. Algorithms used in these programs must be scalable, while being resilient to hardware failures that will happen during the execution. In this presentation, we present an algorithm that takes advantage of intrinsic properties of the scalable communication-avoiding LU algorithms in order to make them fault-tolerant and proceed with the computation in spite of failures. We evaluate the overhead of the fault tolerance mechanisms with respect to failure-free execution on both tall- and-skinny matrices (TSLU) and square matrices (CALU), and the cost of a failure during the execution.
LOVE 17/06/2021 [Séminaire Chocola] Focused nested calculi applied to the logic of bunched implications, par Sonia Marin
Sonia Marin, University College London  
https://chocola.ens-lyon.fr/events/online-2021-06-17/talks/marin/
17/06/2021    10:00 - 12:00
Résumé :
Focusing is a general technique for syntactically compartmentalising the non-deterministic choices in a proof system, which not only improves proof search but also has the representational benefit of distilling sequent proofs into synthetic normal forms. However, since focusing was traditionally specified as a restriction of the sequent calculus, the technique had not been transferred to logics that lack a (shallow) sequent presentation, as is the case for some modal or substructural logics. With K. Chaudhuri and L. Straßburger, we extended the focusing technique to nested sequents, a generalisation of ordinary sequents which allows us to capture all the logics of the classical and intuitionistic S5 cube in a modular fashion. This relied, following the method introduced by O. Laurent, on an adequate polarisation of the syntax and an internal cut-elimination procedure for the focused system which in turn is used to show its completeness. Recently, with A. Gheorghiu, we applied a similar method to the logic of Bunched Implications (BI), a logic that freely combines intuitionistic logic and multiplicative linear logic. For this we had first to reformulate the traditional bunched calculus for BI using nested sequents, followed by a polarised and focused variant that (again) we show is sound and complete via a cut-elimination argument.
LOVE 03/06/2021 [Séminaire Chocola] Internalizing Representation Independence with Univalence, par Carlo Angiuli
Carlo Angiuli, Carnegie Mellon University  
https://chocola.ens-lyon.fr/events/online-2021-06-03/talks/angiuli/
03/06/2021    15:00 - 17:00
Résumé :
In their usual form, representation independence metatheorems provide an external guarantee that two implementations of an abstract interface are interchangeable when they are related by an operation-preserving correspondence. In the dependently-typed setting, however, we would like to appeal to such invariance results within a language itself, in order to transfer theorems from simple to complex implementations. Homotopy type theorists have noted that Voevodsky's univalence principle equates isomorphic structures, but unfortunately many instances of representation independence are not isomorphisms. In this talk, we describe a technique for establishing internal relational representation independence results in Cubical Agda by using higher inductive types to simultaneously quotient two related implementation types by a heterogeneous correspondence between them. The correspondence becomes an isomorphism between the quotiented types, thereby allowing us to obtain an equality of implementations by univalence. Joint work with Evan Cavallo, Anders Mörtberg, and Max Zeuner. Available at https://dl.acm.org/doi/10.1145/3434293.
RCLN 31/05/2021 Knowledge-based Detection of Automatically Generated Text, par Vijini Liyanage
Vijini Liyanage, LIPN  
Salle A303, Bâtiment A, LIPN
31/05/2021    13:00 - 14:00
Résumé :
Séminaire de Vijini Liyanage, étudiante du groupe RCLN, qui va nous présenter son sujet de thèse et les premières étapes de sa thèse sur la détection des textes générés automatiquement par des modèles de langage neuronales, du genre GPT-2.
AOC 20/05/2021 Decomposition methods and column/matrix generation approaches for quadratic programming, par Lucas Létocart
Lucas Létocart, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
20/05/2021    10:30 - 11:30
Résumé :
The purpose of this talk is to present three decomposition approaches for quadratic problems. First, we analyze a simplicial decomposition like algorithmic framework that handles convex quadratic programs in an effective way. We also propose a branch & bound approach based on this simplicial decomposition for the binary case and we introduce warmstart techniques using columns' projection. Then, we propose a methodological analysis on a family of reformulations combining Dantzig-Wolfe decomposition and Quadratic Convex Reformulation principles for binary quadratic problems. Finally, we propose a matrix generation method for quadratically constrained 0-1 quadratic problems based on a Dantzig-Wolfe reformulation. The domain of this relaxation corresponds to the Boolean Quadric Polytope.
LOVE 20/05/2021 [Séminaire Chocola] Monads, equational theories, and metrics for nondeterministic and probabilistic systems, par Valeria Vignudelli
Valeria Vignudelli, ENS Lyon  
https://chocola.ens-lyon.fr/events/online-2021-05-20/
20/05/2021    10:00 - 12:00
Résumé :
Monads and their presentations via equational theories provide a tool for reasoning about programs with computational effects. In recent works, we have studied monads resulting from the combination of nondeterminism, probabilities, and termination, as well as their extensions to the category of metric spaces. In this talk, we'll introduce this framework and show applications to proving equivalences and distances of nondeterministic and probabilistic systems. Bibliography: Bonchi, Sokolova, Vignudelli. The theory of traces for systems with nondeterminism and probabilities. LICS 2019. Available at: https://arxiv.org/abs/1808.00923 Mio, Vignudelli. Monads and quantitative equational theories for nondeterminism and probabilities. CONCUR 2020. Available at: https://arxiv.org/abs/2005.07509 Mio, Sarkis, Vignudelli. Combining nondeterminism, probability, and termination: equational and metric reasoning. LICS 2021. Available at: https://arxiv.org/abs/2012.00382
LOVE 06/05/2021 [Séminaire Chocola] Fixpoint Theory -- Upside Down, par Barbara König
Barbara König, Universität Duisburg-Essen  
https://chocola.ens-lyon.fr/events/online-2021-05-06/
06/05/2021    10:00 - 12:00
Résumé :
Knaster-Tarski's theorem, characterising the greatest fixpoint of a monotone function over a complete lattice as the largest post-fixpoint, naturally leads to the so-called coinduction proof principle for showing that some element is below the greatest fixpoint (e.g., for providing bisimilarity witnesses). The dual principle, used for showing that an element is above the least fixpoint, is related to inductive invariants. This talks considers proof rules which are similar in spirit but for showing that an element is above the greatest fixpoint or, dually, below the least fixpoint. The theory is developed for non-expansive monotone functions on suitable lattices of the form M^Y, where Y is a finite set and M an MV-algebra, and it is based on the construction of (finitary) approximations of the original functions. We show that our theory applies to a wide range of examples, including termination probabilities, behavioural distances for probabilistic automata and bisimilarity. Moreover it allows us to determine original algorithms for solving simple stochastic games.
AOC 22/04/2021 Extraction et partitionnement pour la recherche de régularités : application à l'analyse de dialogues., par Zacharie ALES
Zacharie ALES, ENSTA Paris | Institut Polytechnique de Paris  
Salle B107, bâtiment B, Université de Villetaneuse
22/04/2021    10:30 - 11:30
Résumé :
Dans le cadre de l'aide à l'analyse de dialogues, un corpus de dialogues peut être représenté par un ensemble de tableaux d'annotations encodant les différents énoncés des dialogues. Afin d'identifier des schémas dialogiques mis en œuvre fréquemment, nous définissons une méthodologie en deux étapes : extraction de motifs récurrents, puis partitionnement de ces motifs en classes homogènes constituant des régularités. Deux méthodes sont développées afin de réaliser l'extraction de motifs récurrents : LPCA-DC et SABRE. La première est une adaptation d'un algorithme de programmation dynamique tandis que la seconde est issue d'une modélisation formelle du problème d'extraction d'alignements locaux dans un couple de tableaux d'annotations. Le partitionnement de motifs récurrents est réalisé par deux formulations originales du problème de K-partitionnement sous la forme de programmes linéaires en nombres entiers. Lors d'une étude polyèdrale, nous caractérisons des facettes d'un polyèdre associé à ces formulations (notamment les inégalités de 2-partitions, les inégalités 2-chorded cycles et les inégalités de clique généralisées). Ces résultats théoriques permettent la mise en place d'un algorithme de plans coupants résolvant efficacement le problème. Nous développons le logiciel d'aide à la décision VIESA, mettant en œuvre ces différentes méthodes et permettant leur évaluation au cours de deux expérimentations réalisées par un expert psychologue. Des régularités correspondant à des stratégies dialogiques que des extractions manuelles n'avaient pas permis d'obtenir sont ainsi identifiées.
LOVE 22/04/2021 [Séminaire Chocola] The Time and Space of Interaction, par Gabriele Vanoni
Gabriele Vanoni, Università di Bologna  
https://chocola.ens-lyon.fr/events/online-2021-04-22/
22/04/2021    10:00 - 12:00
Résumé :
Girard's Geometry of Interaction (GOI) can be made concrete by considering it as an implementation technique for functional programs, in particular the lambda calculus. Our work is about the complexity analysis of the abstract machine based on the GOI, the interaction abstract machine (IAM). We have adapted in a non trivial way de Carvalho's non idempotent intersection types so that type derivations completely characterize the time and space complexity of the IAM, thus providing a logical account of the IAM resource usage. Moreover, by the way of the type systems we have introduced, we are able to state some negative results about time and space cost models for the lambda calculus based on the IAM. This is joint work with Beniamino Accattoli and Ugo Dal Lago.
AOC 15/04/2021 Formulations PLNE pour un problème d'ordonnancement juste-à-temps, par Anne-Elisabeth FALQ
Anne-Elisabeth FALQ, Sorbonne université, CNRS, LIP6, équipe RO  
Salle B107, bâtiment B, Université de Villetaneuse
15/04/2021    10:30 - 11:30
Résumé :
Une contrainte essentielle pour un problème d'ordonnancement sur une machine est le non-chevauchement des tâches: deux tâches ne peuvent être exécutées en même temps. Les premières inégalités de non-chevauchement ont été proposées par Queyranne (1993) pour le problème de minimisation de la somme pondérée des dates de fins. La famille d'inégalités linéaires proposée décrit exactement l'enveloppe convexe des vecteurs encodant des ordonnancements réalisables par les dates de fins des tâches. Ces inégalités ne coupent pas tous les vecteurs encodant un ordonnancement avec chevauchement mais assurent le non-chevauchement au sens où tous les points extrêmes du polyèdre qu'elles définissent encodent des ordonnancements réalisables, et plus précisément ceux calés à gauche qui forment un ensemble dominant pour ce problème. Dans cet exposé, nous nous intéresseront particulièrement au problème d'ordonnancement juste-à-temps où toutes les tâches partagent une même date d'échéance commune et où il s'agit de minimiser la somme pondérée des avances et des retards par rapport à cette date. En s'appuyant sur les propriétés de dominance connues pour ce problème NP-difficile (Hall et Posner, 1991), nous proposerons une formulation basée sur des inégalités de non-chevauchement nouvelles. Cette formulation, qui n'est pas exactement un programme linéaire en nombre entiers (PLNE) puisqu'elle fait apparaître des contraintes d'extremalité, peut être résolue par un solveur de PL implémentant un algorithme de "Branch-and-Cut". Nous expliquerons comment et présenterons quelques résultats expérimentaux. Dans un second temps, nous proposerons une formulation compacte pour ce problème, que nous renforçons par des inégalités dites de dominance. Ces inégalités sont ainsi nommées car elles traduisent la dominance des solutions localement optimales, où local s'entend pour un voisinage généré par une famille d'opérations sur les solutions. Pour chaque opération considérée, une inégalité élimine les solutions qu'on pourrait améliorer en appliquant la transformation. De ce fait, ces inégalités coupent des point entiers, et diffèrent en cela des inégalités classiques de renforcement. Grâce à des résultats expérimentaux, nous montrerons le gain d’efficacité qu'apporte ces inégalités de dominance.
LOVE 15/04/2021 Categorifying Non-Idempotent Intersection Types, par Giulio Guerrieri
Giulio Guerrieri, University of Bath  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (code d'accès: 749983)
15/04/2021    10:00 - 11:00
Résumé :
Non-idempotent intersection types can be seen as a syntactic presentation of a well-known denotational semantics for the lambda-calculus, the category of sets and relations. Building on previous work, we present a categorification of this line of thought in the framework of bang calculus, an untyped version of Levy's call-by-push-value. We define a bicategorical model for the bang calculus, whose syntactic counterpart is a suitable category of types. In the framework of distributors, we introduce intersection type distributors, a bicategorical proof relevant refinement of relational semantics. Finally, we prove that intersection type distributors characterize normalization at depth 0. This is joint work with Federico Olimpieri, published at CSL 2021.
LOVE 08/04/2021 [Séminaire Chocola] Sketching type theories, par Daniel Gratzer
Daniel Gratzer, Aarhus University  
https://chocola.ens-lyon.fr/events/online-2021-03-25/
08/04/2021    10:00 - 12:00
Résumé :
Recent developments in type theory have attempted to systematically recast properties of the syntax of a type theories (canonicity, normalization, etc.) into equivalent questions about the category of models. This dictionary relies on a formal link between the syntax of a theory and its category of models: the syntax of the theory must organize into an initial model. To expedite this process, several logical frameworks have been proposed which provide schemata for defining a type theory so that it automatically determines a category of models in which syntax is initial. In this talk, rather than giving a new logical framework per se, we propose a new discipline for creating logical frameworks based around finitary 2-monads and sketches. As a case study of this approach, we show how locally Cartesian closed categories provide a suitable doctrine for type theories. We illustrate how a general theory of sketches [KPT99] can be used to define syntactic categories for type theories in a style that resembles the use of Martin-Löf's Logical Framework [NPS90], following the "judgments as types" principle [HHP93, ML87]. We prove a semantic adequacy result for locally Cartesian closed categories relative to Uemura's representable map categories [Uem19]: if a theory is definable in the framework of Uemura, the locally Cartesian closed category that it generates is a conservative (fully faithful) extension of its syntactic representable map category. On this basis, we argue for the use of locally Cartesian closed categories as a simpler alternative to Uemura's representable map categories. This is joint work with Jonathan Sterling, and a preprint is available on arxiv: https://arxiv.org/abs/2012.10783
LOVE 07/04/2021 Approche formelle pour la vérification formelle de la composition de logiciels, par Mohamed Graiet
Mohamed Graiet  
https://bbb.lipn.univ-paris13.fr/b/ari-uht-t3u
07/04/2021    09:00 - 10:00
Résumé :
La réutilisation est un concept clé dans la construction de systèmes logiciels. Elle permet de composer un ensemble de logiciels existants pour construire de nouveaux logiciels à valeur ajoutée. Dans le contexte de notre travail, on s'intéresse à la composition de deux types de logiciels, à savoir les services Web et logiciels libres à base de packages FOSS (Free and Open Source Software). La vérification de la correction de la composition pour la sécurité de logiciels FOSS et de services Web reste l’une des tâches les plus difficiles malgré les efforts et les travaux de recherches entrepris. Un service composé est déclaré correct s’il respecte un ensemble d’exigences de deux types: les exigences transactionnelles et de QoS (la sécurité des exigences métiers). Les exigences de QoS sont définies sous la forme d’un contrat SLA (service-level agreement). Un contrat SLA est un ensemble de contraintes de QoS. Les exigences transactionnelles sont spécifiées par les concepteurs en utilisant le concept d’états de terminaison acceptés (ETA). Un logiciel composite FOSS est dit correct s’il respecte un ensemble de contraintes de dépendances et de capacités. Pour parvenir à résoudre ce problème de vérification, nous proposons une approche formelle fondée sur la méthode Event-B. Une telle approche se résume en deux points: i) Une formalisation Event-B de la composition de services avec Event-B. ii) Une formalisation Event-B de la composition de logiciels FOSS dans un contexte cloud. Ces deux formalisations sont validées en se servant des obligations de preuves et d’un model-checker ProB. La formalisation de la composition de services se repose sur les trois étapes suivantes: - Etape 1: formalisation des services Web. - Etape 2: formalisation de la composition statique de services Web. - Etape 3: formalisation de la composition dynamique de services Web. Quant à la deuxième formalisation, elle est construite en deux étapes principales. La première étape concerne la formalisation des logiciels FOSS composites d’une manière générale. Dans la deuxième étape, on raffine cette formalisation par l’introduction des propriétés d’élasticité verticale et horizontale offertes par l'environnement cloud. La propriété d'élasticité verticale permet d'augmenter ou de réduire la capacité des logiciels en ajoutant de nouvelles ressources (logiciels) ou en supprimant celles qui ne sont pas en cours d’utilisation. La propriété d'élasticité horizontale permet d'augmenter ou de diminuer les ressources logicielles en ajoutant de nouvelles copies de composants existants ou en supprimant les inutiles. Pour la mise en œuvre de cette approche nous utilisons une approche à base d’IDM (transformation texte to modèle, modèle to modèle et modèle to texte).
LOVE 01/04/2021 Typing Differentiable Programming, par Marie Kerjean
Marie Kerjean, LIPN, CNRS & Université Sorbonne Paris Nord  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (code d'accès: 749983)
01/04/2021    10:15 - 11:15
Résumé :
Differentiable programming is a recent research area: its objective is to express differentiation as a modular algorithmic transformation on rich programming languages. It is in particular motivated by the various applications of automatic differentiation in machine learning or formal calculus. In this talk I will present joint work with Pierre-Marie Pédrot, focusing on the typing system used to express differentiation. We will first review a few examples of differentiable languages recently exhibited in the literature. This allows to identity the linear Dialectica transformation as a reverse automated differentiation transformation on a higher-order lambda-calculus with positive types. Building on the intuitions provided by Dialectica and distribution theory, we construct a lambda-calculus with an internal differentiation operator. This calculus is typed by a type system inspired by Differential Linear Logic. Noticeably, we are able to express backward automatic differentiation as an evaluation strategy.
LOVE 30/03/2021 Reducing the Security Assessment for Industrial Cyber-Physical Systems against Smart Attacks , par Samir Ouchani
Samir Ouchani, Lineact CESI (Aix-en-Provence, France)  
https://bbb.lipn.univ-paris13.fr/b/ari-uht-t3u
30/03/2021    10:30 - 11:30
Résumé :
Industrial cyber-physical systems (ICPS) are heterogeneous inter-operating parts that can be physical, technical, networking, and even social-like agent operators. Incrementally, they perform a central role in critical and industrial infrastructures, governmental, and personal daily life. Especially with the Industry 4.0 revolution, they became more dependent on connectivity by supporting novel communication and distance control functionalities, which expand their attack surfaces that result in a high risk for cyber-attacks. Further, regarding physical and social constraints, they may push up new classes of security breaches that might result in serious economic damages. Thus, designing a secure ICPS is a complex task that has to guarantee security and harmonize the functionalities between the various parts that interact with different technologies. This talk highlights the significance of cyber-security infrastructure and shows how to evaluate, prevent, and mitigate ICPS-based cyber-attacks. First, I will take this opportunity to introduce myself and briefly present my ongoing research activities. Then, I will present the foundation of a prominent semantics for ICPSÂ’s entities and their composition, which includes social actors that act differently than mobile robots and automated processes. In addition, I will provide the feasible attacks generated by a reinforcement learning mechanism based on multiple criteria that selects both appropriate actions for each ICPS component within the possible countermeasures for mitigation. Finally, I will detail the overall solution that reduces the verification cost and its effectiveness in a real use case scenario.
LOVE 19/03/2021 Avancées récentes sur les algèbres de Kleene concurrentes, par Paul Brunet
Paul Brunet, University College London  
https://bbb.lipn.univ-paris13.fr/b/ari-uht-t3u
19/03/2021    10:30 - 11:30
Résumé :
Les algèbres de Kleene concurrentes (CKA) fournissent un cadre algébrique pour raisonner sur les programmes concurrents. Au cours de ces dernières années, nous avons étudié différentes manières d'enrichir ce modèle afin de capturer une classe plus large de problèmes de vérification. Dans cet exposé, je présenterai tout d'abord les bases de CKA, avec ses présentations axiomatiques et combinatoires, et les résultats de décidabilité correspondants. Je ferais ensuite un bref panorama de certaines extensions du modèle, en considérant des aspects tels que le flot de contrôle, la cohérence des accès mémoire, et l'exclusion mutuelle. Ce travail est le fruit de collaborations avec Tobias Kappé, Jana Wagemaker, Simon Docherty, Fabio Zanasi, Jurriaan Rot, Alexandra Silva, David Pym, Damien Pous, et Georg Struth.
LOVE 19/03/2021 Modeling and formal verification of a communicating autonomous vehicle system, par Johan Arcile
Johan Arcile  
https://bbb.lipn.univ-paris13.fr/b/ari-uht-t3u
19/03/2021    09:00 - 10:00
Résumé :
A system of autonomous vehicles consists of several agents individually making decisions in real time while exchanging information with other agents nearby. The validation of formal logic properties in such systems is not possible through naive approaches, due to the large number of variables involved in their representation. The two complementary works that will be presented have been developed to address this issue: - The VerifCar software framework, dedicated to decision-making analysis of communicating autonomous vehicles, which uses the state-of-art tool Uppaal. - The formalism of MAPTs and its dedicated exploration algorithms, allowing the use of heuristics that reduces the computation time needed to address reachability problems.
LOVE 18/03/2021 Model-checking pour l’agriculture de précision, par Rim Saddem
Rim Saddem  
https://bbb.lipn.univ-paris13.fr/b/ari-uht-t3u
18/03/2021    14:00 - 15:00
Résumé :
Dans cette présentation, je vais vous présenter mon travail de recherche qui comporte deux parties : la première porte sur ce que j’ai effectué durant ma thèse et la deuxième porte sur ce que j’ai effectué durant mon poste ATER. Mon travail de thèse porte sur l’application des techniques de model-checking pour résoudre des problèmes issus de l’agriculture de précision. L’agriculture de précision (AP) s’est fortement développée au cours des dernières décennies avec les progrès des technologies de localisation, des capteurs et des techniques de télédétection. Le principe de l’AP est de rechercher et mettre en œuvre la Bonne action au Bon moment et au Bon endroit ("3B"), avec l’objectif d’améliorer l’efficience de l’agriculture suivant les critères d’une agriculture durable. Pour modéliser et vérifier des opérations agricoles, une représentation des dynamiques temporelles et spatiales est nécessaire. Le model- checking de systèmes d’automates temporisés avec des requêtes dans une logique temporelle arborescente répond à ces besoins, les positions spatiales pouvant être représentées de façon ad-hoc dans le cadre de ces formalismes. Trois exemples d’opérations agricoles ont été considérés dans ce travail. La première est relative au calcul d’une séquence optimale de commandes pour une pulvérisation de précision en viticulture. La seconde concerne la récolte sélective en viticulture. La dernière est relative à la vérification d’une mission de robotique agricole. Nous étudions dans ces exemples l’atteignabilité d’un état cible pour l’opération, ou l’atteignabilité avec un critère de coût optimal. Pour pallier au problème d’explosion combinatoire rencontré dans les cas traités, une méthodologie de décomposition pour le model-checking d’atteignabilité a été développée. Les résultats expérimentaux avec et sans décomposition sont présentés pour les 3 exemples d’opération étudiés. La technique de décomposition est appliquée sur 2 des 3 exemples et les résultats expérimentaux montrent son efficacité. Mon travail durant mon poste ATER propose une extension du formalise des processus métiers pour prendre en considération la représentation spatiale afin de modéliser le comportement des robots.
LOVE 18/03/2021 Transcendental Syntax: the dynamics of logic programs and tilings, applied to Linear Logic, par Boris Eng
Boris Eng, LIPN, Université Sorbonne Paris Nord  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (code d'accès: 749983)
18/03/2021    10:00 - 11:00
Résumé :
The Transcendental Syntax, successor of Girard's Geometry of Interaction programme, aims at a reconstruction of linear logic from computation with finite objects. We define a model of computation we call Stellar Resolution; a graph-theoretical reformulation of Robinson's first-order resolution, which appear to be closely related to geometric tilings. As a first illustration of the Transcendental Syntax's technical content, we show that we can naturally encode both the cut-elimination and logical correctness of MLL proof-structures. Using techniques from realisability, similarly to ludics, we retrieve a very generic notion of linear typing as a description of computational behaviour for programs computing with local and asynchronous interactions.
AOC 17/03/2021 A snapshot of quantum algorithms for optimization, par Giacomo Nannicini
Giacomo Nannicini, IBM - Watson  
Salle B107, bâtiment B, Université de Villetaneuse
17/03/2021    15:00 - 16:00
Résumé :
There is much hype surrounding quantum computing and its potential applications for optimization. However, the technical details are often lost in translation. In this talk I will give an overview of quantum algorithms that may - one day - be useful for continuous and discrete optimization, highlighting possible sources of advantage as well as limitations. In particular, I will discuss variational hybrid algorithms for optimization, simulated annealing for counting problems, algorithms for linear systems, and algorithms for SDPs and LPs. I assume no prior knowledge of quantum mechanics.
AOC 11/03/2021 Learning to solve the single machine scheduling problem with release times and sum of completion times, par Axel Parmentier
Axel Parmentier, ENPC  
Salle B107, bâtiment B, Université de Villetaneuse
11/03/2021    10:30 - 11:30
Résumé :
In this work, we focus on the solution of a hard single machine scheduling problem by new heuristic algorithms embedding techniques from machine learning field and scheduling theory. These heuristics transform an instance of the hard problem into an instance of a simpler one solved to optimality. The obtained schedule is then transposed to the original problem. Computational experiments show that they are competitive with state-of-the-art heuristics, notably on large instances.
LOVE 11/03/2021 [Séminaire Chocola] Machine-Checked Computer-Aided Mathematics, par Assia Mahboubi
Assia Mahboubi, INRIA  
https://chocola.ens-lyon.fr/events/seminaire-2021-03-11/
11/03/2021    10:00 - 12:00
Résumé :
This talk presents an overview of three contributions to the formal verification of mathematics in dependent type theory. The first of these contributions deals with the realization of a library of digitized mathematics, covering the standard undergraduate background in algebra as well as some more advanced chapters in finite group theory. The two other contributions are related to the issues pertaining to the formal verification of computational mathematical proofs, by the means of symbolic algorithms and of rigorous numerical methods respectively. We conclude with a few perspectives on the formal verification of computer-aided mathematics.
LOVE 05/03/2021 Contributions to Boolean satisfiability solving and its application to the analysis of discrete systems, par Souheib Baarir
Souheib Baarir, LIP6 - Université de Paris Nanterre  
https://bbb.lipn.univ-paris13.fr/b/ari-uht-t3u
05/03/2021    14:00 - 15:30
Résumé :
Despite its NP-Completeness, propositional (Boolean) satisfiability (SAT) covers a broad spectrum of applications. Nowadays, it is an active research area finding its applications in many contexts: planning decision, cryptology, computational biology, hardware and software analysis, etc. Hence, the development of approaches that could handle increasingly challenging SAT problems has become a focus. During these last 8 years, SAT solving has been the main subject of my research work, and in this talk I will present some of the main results we obtained in the field.
LOVE 05/03/2021 On the formal verification of safety-critical systems: challenges, approaches and perspectives, par Mohammed Foughali
Mohammed Foughali, VERIMAG  
https://bbb.lipn.univ-paris13.fr/b/ari-uht-t3u
05/03/2021    12:15 - 13:45
Résumé :
Safety-critical applications, e.g. those stemming from robotic, autonomous and cyber-physical systems, must be formally verified against crucial behavioral and timed properties. Yet, the use of formal verification techniques in such context faces a number of challenges, such as the absence of formal foundations of robotic frameworks and the lack of scalability of exhaustive verification techniques. In this talk, I will explore the approaches I have been proposing for the last six years to tackle these challenges, based on a global vision that favors correctness, user-friendliness and scalability of formal methods vis-à-vis real-world robotic and autonomous systems deployed on embedded platforms. I will discuss a major part of my work where safety-critical specifications are automatically translated into strictly equivalent formal models on which model checking, but also scalable non exhaustive techniques such as statistical model checking and runtime verification, may be used by practitioners to gain a considerable amount of trust in their underlying applications. Further, I will present a couple of techniques that allow to take into account hardware and OS specificities in the verification process, such as the scheduling policy and the number of processor cores provided by the platform, and thus increase the meaningfulness of the verification results. I will conclude with possible future research directions within the broad objective of deploying trustable safety-critical systems through bridging the gap between the software engineering, robotics, formal methods and real-time systems communities.
LOVE 04/03/2021 Geometry of Interaction for ZX-Diagrams, par Kostia Chardonnet et Renaud Vilmart
Kostia Chardonnet et Renaud Vilmart, LRI  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (code d'accès: 749983)
04/03/2021    10:30 - 11:30
Résumé :
ZX-Calculus is a versatile graphical language for quantum computation equipped with an equational theory. Getting inspiration from Geometry of Interaction, in this work we propose a token-machine-based asynchronous model of both pure ZX-Calculus and its extension to mixed processes. We also show how to connect this new semantics to the usual standard interpretation of ZX-diagrams. This model allows us to have a new look at what ZX-diagrams compute, and give a more local, operational view of the semantics of ZX-diagrams.
LOVE 25/02/2021 [Séminaire Chocola] Titre bientôt disponible, par Zeinab Galal
Zeinab Galal, IRIF, Université de Paris  
http://chocola.ens-lyon.fr/events/online-2021-02-25/
25/02/2021    10:00 - 12:00
Résumé :
AOC 18/02/2021 Combinatorial Optimization Theory and Algorithms for Set Packing and Location Problems, par Mercedes Pelegrin
Mercedes Pelegrin, LIX  
Salle B107, bâtiment B, Université de Villetaneuse
18/02/2021    10:30 - 11:30
Résumé :
In this talk, we will cover modeling for two optimization problems, as well as Mathematical Programming methods that can be applied to solve them. The first part will be devoted to the set packing problem, one of the seminal problems in Combinatorial Optimization. We will focus on generating hyperplanes to describe the set packing polytope. Namely, we will present a new lifting theorem and illustrate its application to facility location. In the second part of the talk, we will address the problem of identifying a group of key nodes in a network. We will propose a mixed integer nonlinear program (MINLP) that embeds eigenvector centrality in a clustering partition. The resulting model uncovers the group of key nodes (the clusters centroids) and their communities (the clusters). Modeling this idea involves nonlinear equations, which will be linearized to produce a mixed integer linear program (MILP). Symmetry breaking, a recurrent topic in Combinatorial Optimization, will be also addressed. Computational results on synthetic and real-life networks will be presented.
LOVE 18/02/2021 Enriched concurrent games: witnesses for proofs and resource analysis, par Aurore Alcolei
Aurore Alcolei, Università di Bologna  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (code d'accès: 749983)
18/02/2021    10:00 - 11:00
Résumé :
Game semantics is known as the semantics of control flow and interactions. Among its various models, causal game models emphasize the causal relation between the computational events that describe these interactions. This view point is particularly suitable to represent parallel computations and concurrent behaviours. In this talk I will show how causal game models can be enriched with annotations in order to capture side computations, that are, computational information that varies with the control flow but does not affect it. This enrichment will motivated through two semantics problems in both logics and programming: - Offering a novel compositional interpretation of Herbrand theorem by capturing the structure of Herband witnesses as causal strategies annotated with terms; - Enriching a sound and adequate concurrent game model for higher order concurrent programs with quantitative information in order to reflect their minimal execution time.
AOC 11/02/2021 Linearization techniques for MINLP, par Sandra Ulrich Ngueveu
Sandra Ulrich Ngueveu, LAAS-CNRS  
Salle B107, bâtiment B, Université de Villetaneuse
11/02/2021    10:30 - 11:30
Résumé :
We review state-of-the-art linearization and approximation techniques for the solution of non-linear mixed-integer programs. We show in particular how to ensure an a priori guarantee on the quality/feasibility of the solution, a reduction of the size of the converted problem and a minimization of the computing time. We then present an iterative method for the solution of a class of non-linear mixed-integer programs to arbitrary numerical precision. By keeping the scope of the update local from one iteration to another, the computational burden is only slightly increased from iteration to iteration. As a consequence, our method presents very nice scalability properties and is little sensitive to the desired precision. We assess its efficiency for approximating the non-linear variants of three problems: the uncapacitated facility location problem, the multi-commodity network design problem, and the transportation problem. Our results indicate that, as the desired precision becomes smaller, our approach can lead to significant gains in computing times, often being orders of magnitude faster than a baseline method, and scales to approximate larger problems.
LOVE 11/02/2021 [Séminaire Chocola] Sequentiality, References and Well-bracketing in the pi-calculus, par Enguerrand Prebet
Enguerrand Prebet, ENS Lyon  
http://chocola.ens-lyon.fr/events/online-2021-02-11/
11/02/2021    10:00 - 12:00
Résumé :
The pi-calculus is used as a model for programming languages. Its contexts exhibit arbitrary concurrency, making them very discriminating. This may prevent validating desirable behavioural equivalences in cases when more disciplined contexts are expected. We formalise using types three different disciplines: sequentiality or the idea of having a single thread of computation ; reference types for which channels behave like bits of store or atomic register ; and well-bracketing which strengthens the sequentiality constraints to also obey a stack-like discipline. For each, we present the type system along with its consequences on behavioural equivalence and the corresponding bisimulation techniques.
LOVE 09/02/2021 Symbolic Verification Techniques for Multiparty Interaction, par Carlos Olarte
Carlos Olarte, Federal University of Rio Grande do Norte (Brazil)  
https://bbb.lipn.univ-paris13.fr/b/ari-uht-t3u
09/02/2021    12:00 - 13:00
Résumé :
Multiparty interactions are commonplace in today's distributed systems. An agent usually communicates, in a single session, with other agents to accomplish a given task. Take for instance an online transaction including the credit card system, the vendor and the client. What we observe is a single transaction composed of several (binary) interactions leading to changes in the state of all the involved agents. Multiway synchronization process calculi, that move from a binary to a multiparty synchronization discipline, have been proposed to formally study the behavior of those systems. For instance, the Core Network Algebra (CNA) extends the point-to-point communication discipline of Milner's CCS with link-chains, describing how information flows among the agents. In this model, the number of participants in an interaction cannot be fixed a priori, and hence, CNA computations are inherently non-deterministic. This leads to an exponential blow-up in the number of reachable states and makes it difficult to devise verification techniques for this formalism. In this talk, I will show four mechanisms that we have proposed for tackling this problem. Namely: (1) A symbolic semantics and bisimulation for CNA that are more amenable for automated reasoning. Symbolic configurations represent, compactly, a possibly infinite number of states and they can be effectively checked. (2) The Symbolic Link Modal Logic, a smooth extension of Hennessy-Milner logic that faithfully characterizes the (symbolic) transitions of CNA processes. (3) An extension of CNA with constraints that declaratively allow the modeler to restrict the interactions that should actually happen. Our definition of constraints is general enough, and it offers the possibility of accumulating costs in multiparty negotiations. This extension finds applications in the modeling of Service Level Agreement protocols and balancing the interactions in a concurrent system. (4) A suitable representation of the above techniques as an executable rewrite theory. Our implementation of this theory in Maude offers the possibility of animating CNA specifications, and it provides (automatic) verification procedures to analyze them.
LOVE 04/02/2021 A uniform framework for substructural logics with modalities , par Elaine Pimentel
Elaine Pimentel, Universidad Federal del Rio Grande do Norte  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (code d'accès: 749983)
04/02/2021    14:00 - 15:00
Résumé :
In this work we investigate such a local system for linear logic (LL) based on linear nested sequents (LNS). Relying on that system, we propose a general framework for modularly describing systems combining, coherently, substructural behaviors inherited from LL with simply dependent multimodalities. This class of systems includes linear, elementary, affine, bounded and subexponential linear logics and extensions of multiplicative additive linear logic (MALL) with normal modalities, as well as general combinations of them. (joint work with Björn Lellmann and Carlos Olarte).
AOC 28/01/2021 Postier chinois dans les triangulations planaires et applications à la chimie, par Matej Stehlik
Matej Stehlik, INP Grenoble  
Salle B107, bâtiment B, Université de Villetaneuse
28/01/2021    10:30 - 11:30
Résumé :
Le problème du postier chinois est un problème classique de l’optimisation combinatoire. Dans cet exposé, je me concentrerai sur le problème du postier chinois dans les triangulations planaires. Je montrerai une borne optimale sur la longueur du plus court parcours de postier, et je discuterai des liens à la chimie théorique.
LOVE 28/01/2021 [Séminaire Chocola] Stable Relations and Abstract Interpretation of Higher-Order Programs, par Benoît Montagu
Benoît Montagu, INRIA  
http://chocola.ens-lyon.fr/events/online-2021-01-28/
28/01/2021    10:00 - 12:00
Résumé :
We present a novel denotational semantics for the untyped call-by-value ?-calculus, where terms are interpreted as stable relations, i.e. as binary relations between substitutions and values, enjoying a monotonicity property. The denotation captures the input-output behaviour of higher-order programs, and is proved sound and complete with respect to the operational semantics. Following the principles of abstract interpretation, we use our denotational semantics as a collecting semantics to derive a modular relational analysis for higher-order programs. The analysis infers equalities between the arguments of a program and its results---a form of frame condition for functional programs.
LOVE 26/01/2021 Vérification formelle de systèmes distribués et de leurs propriétés réseau, par Nicolas SCHNEPF
Nicolas SCHNEPF  
Salle A303
26/01/2021    12:00 - 13:30
Résumé :
L’emploi de méthodes formelles est aujourd’hui plus que jamais nécessaire pour assurer la vérification ou la synthèse de politiques réseau assurant les propriétés de sûreté et de sécurité requises par les systèmes distribués contemporains. Dans cet exposé je présenterai mes travaux de thèse autour de l’orchestration et de la vérification formelle de fonctions de sécurité pour des environnements intelligents tels que des smartphones ou des tablettes, après quoi j’aborderai les résultats d’un article récemment accepté à Tacas 2021 dans le cadre de mon postdoc portant sur la vérification quantitative de réseaux sous condition de pannes de liens. Finalement je présenterai les collaborations que j’envisage avec votre équipe, en particulier en termes de vérification modulaire d’architectures multi-protocoles mais également en termes d’utilisation de méthodes formelles pour prouver les propriétés de sécurité d’architectures distribuées multi-agents ou encore pour détecter des applications malveillantes à plusieurs niveaux d’observation.
LOVE 21/01/2021 Extensional denotational semantics of probabilistic programs, beyond the discrete case, par Guillaume Geoffroy
Guillaume Geoffroy, Università di Bologna  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (code d'accès: 749983)
21/01/2021    10:00 - 11:00
Résumé :
The idea of extensional denotational semantics is to interpret first-order probabilistic programs as measure transformers. For example, a program that takes as input a handle to a random generator of real numbers and outputs a randomly chosen real number is interpreted as a map that takes a sub-probability measure on R and returns a sub-probability measure on R. Beyond first order, “extensional” means that each type is interpreted as a set with some additional structure, and programs as structure-preserving maps. The question of what structure exactly is a long-standing one. We will see in what way the structures that have been proposed so far are not completely satisfactory as soon as non-discrete probabilities are involved, why such a structure should at least include that of an algebra over the monad of sub-probability measures, and an example of structure that seems to fit the bill.
LOVE 14/01/2021 [Séminaire Chocola] Taylor Subsumes Scott, Berry, Kahn and Plotkin, par Giulio Manzonetto
Giulio Manzonetto, LIPN, Université Sorbonne Paris Nord  
http://chocola.ens-lyon.fr/events/seminaire-2021-01-14/
14/01/2021    10:00 - 12:00
Résumé :
The speculative ambition of replacing the old theory of program approximation based on syntactic continuity with the theory of resource consumption based on Taylor expansion and originating from the differential lambda-calculus is nowadays at hand. Using this resource sensitive theory, we provide simple proofs of important results in lambda-calculus that are usually demonstrated by exploiting Scott's continuity, Berry's stability or Kahn and Plotkin's sequentiality theory. A paradigmatic example is given by the Perpendicular Lines Lemma for the Böhm tree semantics, which is proved here simply by induction, but relying on the main properties of resource approximants: strong normalization, confluence and linearity.
LOVE 18/12/2020 On higher-order cryptography, par Raphaëlle Crubillé
Raphaëlle Crubillé, LORIA  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (access code: 749983)
18/12/2020    15:15 - 16:15
Résumé :
Type-two constructions abound in cryptography: adversaries for encryption and authentication schemes, if active, are modeled as algorithms having access to oracles, i.e. as second-order algorithms. But how about making cryptographic schemes themselves higher-order? This work gives an answer to this question, by first describing why higher-order cryptography is interesting as an object of study, then showing how the concept of probabilistic polynomial time algorithm can be generalized so as to encompass algorithms of order strictly higher than two, and finally proving some positive and negative results about the existence of higher-order cryptographic primitives, namely authentication schemes and pseudorandom functions.
LOVE 17/12/2020 History-Dependent Nominal mu-Calculus, par Clovis Eberhart
Clovis Eberhart , ERATO MMSD project, Tokyo  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (code d'accès: 749983)
17/12/2020    10:30 - 11:30
Résumé :
The mu-calculus with atoms, or nominal mu-calculus, is a temporal logic for reasoning about transition systems that operate on data atoms coming from an infinite domain and comparable only for equality. It is, however, not expressive enough to define some properties that are of interest from the perspective of system verification. To rectify this, we extend the calculus with tests for atom freshness with respect to the global history of transitions. Since global histories can grow arbitrarily large, it is not clear whether model checking for the extended calculus is decidable. We prove that it is, by showing that one can restrict attention only to locally relevant parts of the history. This is joint work with Bartek Klin.
AOC 17/12/2020 Combinatorial Optimization problems in telecommunication networksitre bientôt disponible, par Sébastien Martin
Sébastien Martin, NTO team from DataCom Department, Huawei Technologies Co.,Ltd.  
Salle B107, bâtiment B, Université de Villetaneuse
17/12/2020    10:30 - 11:30
Résumé :
The telecommunication network area provides lot of interesting optimization problems. Furthermore, the arrival of 5G technology modifies the traditional combinatorial optimization problems by adding some specificities. We quickly present some case studies done by the "network optimization" team from "Datacom" department. For instance, we present the "network slicing technology" ensuring isolation in resource sharing among users. We also describe the "Deterministic Networking" to guarantee bounded jitter and latency constraints. Finally, we show how to consider network calculus in optimization problems to ensure latency guarantees. We finish by the presentation of future telecommunication network topics from an optimization point of view. Joint work with Nicolas Huin, Jérémie Leguay, Youcef Magnouche, Paolo Medagliani
LOVE 14/12/2020 Measurable Game Semantics, par Hugo Paquet
Hugo Paquet, University of Oxford  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (access code: 749983)
14/12/2020    10:00 - 11:00
Résumé :
I will present recent work on a denotational semantics for probabilistic programs based on games and strategies. This is a probabilistic enrichment of concurrent games on event structures, a model extensively developed in the past few years by Winskel, Clairambault, Castellan and others. Concurrent games have been used successfully to model computation with discrete probability; applications include full abstraction results for probabilistic extensions of PCF and the pure lambda-calculus. I will focus on an extension of the above with measure-theoretic structure. The resulting category supports higher-order types, continuous probability distributions, and primitives for conditioning, and can be used to model both call-by-value and call-by-name.
RCLN 07/12/2020 wikiSERA: Domain independent evaluation of automatic summaries using relevance analysis on Wikipedia, par Jorge Garcia Flores
Jorge Garcia Flores, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
07/12/2020    12:30 - 13:30
Résumé :
Text summarization has been the subject of increasing research efforts in the last years. However, automatic summary evaluation is as crucial as the summarization task itself. For more than 15 years, the dominant approach for evaluating this task has been ROUGE [Lin, 2004], a machine translation inspired lexical comparison between a candidate machine summary and a set of human gold standard summaries. Lexical comparison might be a suitable evaluation approach for extractive summarization systems. However, the methodological leap of Deep Learning brought increasing research efforts on abstractive summarization, which raised some questions about the pertinence of an all-lexical evaluation perspective. In this work we present wikiSERA, an open source improvement of the SERA evaluation method [Cohan et al., 2018], based on a semantic comparison of information extraction vectors from a document base. We adapted the method to generic domain summarization and provide to the community a Wikipedia based implementation that shows robust correlation with human evaluations. --- Après le séminaire on va saluer Jorge qui nous quitte pour quelques mois, avec un apéro de "résistance" (contre la Covid, la LPR, etc..)
AOC 03/12/2020 Geometric Set Cover via Randomized LP Rounding, par Mustafa Nabil
Mustafa Nabil, ESIEE Paris and LIGM  
Salle B107, bâtiment B, Université de Villetaneuse
03/12/2020    10:30 - 11:30
Résumé :
Geometric set-cover/hitting-set problems arise naturally in several basic settings, and therefore the problem of computing small set covers (and hitting sets) has been studied extensively. A common first step in solving such optimization problems is to formulate and solve the corresponding covering/packing LP to get a fractional solution. Then the task reduces to constructing an integer solution from this fractional solution. In this talk, I will present a new simple iterative randomized rounding scheme that gives optimal approximation bounds, within constant factors, for many well-studied geometric systems.
AOC 26/11/2020 Émergence de nouveaux problèmes combinatoires pour les systèmes de production dans le contexte Industrie 4.0, par Paolo Gianessi
Paolo Gianessi, EMSE - Saint-Etienne  
Salle B107, bâtiment B, Université de Villetaneuse
26/11/2020    10:30 - 12:00
Résumé :
Du fait des nouveaux paradigmes de production imposés par l'Industrie 4.0 et de l'attention grandissante portée par l'opinion publique à l'égard des questions environnementales, les systèmes de production doivent relever le double défi de répondre à une demande de plus en plus variable mais aussi faire preuve d'une efficacité énergétique accrue. De nouveaux problèmes combinatoires ont ainsi commencé à paraître dans la littérature de l'Optimisation des systèmes de production à coté des problèmes plus traditionnels. Nous en présentons ici trois, que nous avons étudiés au cours de ces deux dernières années, et qui touchent à la planification stratégique ou tactique/opérationnelle: un problème d'ordonnancement de type job-shop avec prise en compte de l'énergie; un problème d'équilibrage de ligne avec minimisation du pic de puissance; et un problème bi-niveau d'équilibrage de ligne d'un RMS (système de production reconfigurable) visant à minimiser le coût de la consommation énergétique vis-à-vis d'un plan tarifaire donné. Ces problèmes ont pour l'instant été abordés par de premières approches simples (PLNE, méta-heuristiques par décomposition et/où recherche locale) afin d'en démontrer l'intérêt pratique auprès de la communauté industrielle; il paraît tout de même évident qu'ils offrent des développements potentiels à investiguer aussi d'un point de vue plus proprement algorithmique et combinatoire, et par conséquent s'affichent comme de nouveaux éléments d'intérêt certain de la frontière entre applications réelles et recherche fondamentale.
LOVE 26/11/2020 Quantitative Tauberian Theorems, par Thomas Powell
Thomas Powell, University of Bath  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (code d'accès: 749983)
26/11/2020    10:00 - 11:00
Résumé :
In this talk I seek to achieve two things. First, I aim to give a very concise introduction to modern applied proof theory, without assuming any prior knowledge of this area. Second, I will present some new reasearch of mine in Tauberian theory, which studies the convergence of different summation methods for infinite series.
AOC 19/11/2020 A Tight Approximation Algorithm for the Cluster Vertex Deletion Problem, par Samuel Fiorini
Samuel Fiorini, Université libre de Bruxelles  
Salle B107, bâtiment B, Université de Villetaneuse
19/11/2020    10:30 - 11:30
Résumé :
We give the first 2-approximation algorithm for the cluster vertex deletion problem. This is tight, since approximating the problem within any constant factor smaller than 2 is UGC-hard. Our algorithm combines the previous approaches, based on the local ratio technique and the management of true twins, with a novel construction of a 'good' cost function on the vertices at distance at most 2 from any vertex of the input graph. As an additional contribution, we also study cluster vertex deletion from the polyhedral perspective, where we prove almost matching upper and lower bounds on how well linear programming relaxations can approximate the problem.
LOVE 19/11/2020 Introduction to Parametric Verification 2/2, par Laure Petrucci
Laure Petrucci, LIPN, Université Sorbonne Paris Nord  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (code d'accès: 749983)
19/11/2020    10:00 - 11:00
Résumé :
(Filled in by Thomas.) The talk will be the second of two sessions providing a short introduction to parametric verification of concurrent systems. Associated ArXiv paper: https://hal.archives-ouvertes.fr/hal-02170526.
LOVE 12/11/2020 Differentiating stateful processes, par David Sprunger
David Sprunger, ERATO MMSD Project, Tokyo  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (code d'accès: 749983)
12/11/2020    16:00 - 17:00
Résumé :
In this talk, we develop a notion of differentiation for Mealy machines with smooth transition functions. This notion of differentiation is based in the theory of Cartesian differential categories, a synthetic, categorical treatment of differentiation. We exhibit a construction augmenting any Cartesian differential category with a trace-like operation modeling internal state. We apply these categorical constructions to model recurrent neural networks, investigate compositional properties of their derivatives, and ultimately design improved training algorithms in machine learning. Joint work with Shin-ya Katsumata.
AOC 05/11/2020 An exact algorithm for robust influence maximization, par Roberto Wolfler Calvo
Roberto Wolfler Calvo, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
05/11/2020    10:30 - 11:30
Résumé :
We propose a Branch-and-Cut algorithm for the robust influence maximization problem. The influence maximization problem aims to identify, in a social network, a set of given cardinality comprising actors that are able to influence the maximum number of other actors. We assume that the social network is given in the form of a graph with node thresholds to indicate the resistance of an actor to influence, and arc weights to represent the strength of the influence between two actors. In the robust version of the problem that we study, the node thresholds are affected by uncertainty and we optimize over a worst-case scenario within a given robustness budget. Numerical experiments show that we are able to solve to optimality instances of size comparable to other exact approaches in the literature for the non-robust problem, but in addition to this we can also tackle the robust version with similar performance.
LOVE 05/11/2020 Journée Opérades LIPN-LAGA, par Conférence
Conférence  
https://operades20.sciencesconf.org
05/11/2020    09:30 - 16:00
Résumé :
Le programme est disponible en ligne (https://operades20.sciencesconf.org). Pensez à vous inscrire sur le site pour recevoir les informations de connexion. Le premier exposé contiendra une introduction à la théorie des opérades. Liste des orateurs invités: Samuele Giraudo (LIGM, U. Gustave Eiffel), Guillaume Laplante-Anfossi (LAGA, U. Sorbonne Paris Nord), Maxime Lucas (LIPN, U. Sorbonne Paris Nord), Damiano Mazza (LIPN, CNRS).
LOVE 29/10/2020 Mathematical specifications of programming languages via modules over monads, par Ambroise Lafont
Ambroise Lafont, Cogent team, University of New South Wales  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (access code: 749983)
29/10/2020    09:00 - 10:00
Résumé :
Research in the field of programming languages traditionally relies on a definition of syntax modulo renaming of bound variables, with its associated operational semantics. We are interested in mathematical tools allowing us to automatically generate syntax and semantics from basic data. We pay particular attention to the notion of substitution, using the categorical notions of monads and modules over them. Languages with variable binding, such as the pure lambda calculus, are monads on the category of sets. We provide a further notion of transition monads which takes into account the operational semantics. We give examples of specifications for transition monads, in the spirit of Initial Semantics, where an object is characterized by some initiality property in a suitable category of models.
LOVE 22/10/2020 Introduction to Parametric Verification 1/2, par Laure Petrucci
Laure Petrucci, LIPN, Université Sorbonne Paris Nord  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (code d'accès: 749983)
22/10/2020    10:00 - 11:00
Résumé :
(Filled in by Thomas.) The talk will be the first of two sessions providing a short introduction to parametric verification of concurrent systems. Associated ArXiv paper: https://hal.archives-ouvertes.fr/hal-02170526.
LOVE 15/10/2020 Interaction Laws of Monads and Comonads, par Exequiel Rivas
Exequiel Rivas, Inria  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (code d'accès: 749983)
15/10/2020    10:00 - 11:00
Résumé :
Since Moggi's seminal work, monads have been recognized as a way of capturing computational effects. Following this line, we take a view in which their dual, comonads, can be used to capture some form of environment that can interact with such computations. In this talk, we will present a categorical theory of interaction between monads and comonads, abstracting the execution of a computation in an environment. We will highlight connections to previous categorical constructions such as the Chu construction and gluing in the style of Hasegawa. This is joint work with Shin-ya Katsumata and Tarmo Uustalu.
RCLN 12/10/2020 Person-Independent Multimodal Emotion Detection for Children with High-Functioning Autism, par Annanda Sousa
Annanda Sousa, Université de Galway (Irlande)  
Salle B107, bâtiment B, Université de Villetaneuse
12/10/2020    12:30 - 14:00
Résumé :
The use of affect-sensitive interfaces carries the promise of enhancing human-computer interaction by delivering a system capable of identifying a user's emotions and adapt its content accordingly. Today's technology shows great potential to support children with autism, for example by using computer systems to improve their social skills. Generally, however, this technology does not encompass the potential of affect-sensitive interfaces. This is mainly due to Emotion Detection (ED) models built for the general population usually not performing well when applied to children with autism, who express emotions differently. The aim of this project is therefore to build a person-independent Multimodal Emotion Detection system tailored for children with high-functioning autism for the ultimate goal of applying it to design affect-sensitive interfaces dedicated to children with autism. This is a work in progress and the project expects to build upon the current body of knowledge on methods to apply ED systems to this specific subset of the general population. We expect to apply the overall theoretical and practical design perspectives that arise from this research investigation (e.g. analysis of modalities and features extraction, behavioural cues based features, fusion layers and classifier techniques) to propose a guiding framework for future studies.
LOVE 08/10/2020 On Higher-Order (In)Efficiencies, par Gabriele Vanoni
Gabriele Vanoni, Università di Bologna  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (code d'accès: 749983)
08/10/2020    10:00 - 11:00
Résumé :
Intersection types (IT) for the lambda-calculus extend simple types with an intersection operator. They are able to characterize crucial qualitative properties of programs, such as strong, weak and head normalization, and they have been extensively studied for their connections with models and semantics of programming languages. Moreover, considering a variation of the type system in which the intersection is non-idempotent, has led to new quantitative results and simplified many proofs, in the very same way linear logic did, i.e. taking into account the use of resources. This way, non-idempotent IT are able to characterize, for example, the number of steps KrivineÂ’s machine needs to evaluate a term. We show how altering the way in which weights are assigned gives the number of steps the Interaction Abstract Machine (IAM) needs to evaluate a term. This way, we quantitatively observe that the inefficiencies of the IAM come from the presence of higher-order types in the IT derivation. This is joint work with Beniamino Accattoli and Ugo Dal Lago.
LOVE 01/10/2020 Cons-free programs for functional complexity classes, par Siddharth Bhaskar
Siddharth Bhaskar, DIKU, University of Copenhagen  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (code d'accès: 749983)
01/10/2020    10:00 - 11:00
Résumé :
The "cons-free programs" of Neil Jones, in which data can be destructed but not constructed, capture relational LOGSPACE or PTIME over strings, depending on whether we allow tail recursion or general recursion. By generalizing cons-free programs to "RW-factorizable programs," in which there are separate construct-only and destruct-only data types, we recover functional LOGSPACE and PTIME over strings. This seems to be a novel implicit characterization of these classes. RW-factorizable programs faithfully express several natural algorithms. In particular, we study RW-factorizable comparison sorting, prove a quadratic lower bound on the running time of all such sorting programs, and show that this is tight. Finally we conclude with some thoughts about a program for "comparative implicit computational complexity," based on studying indexings of complexity classes obtained from various implicit characterizations.
RCLN 28/09/2020 Recherche d’experts à partir de publications scientifiques, par Stella Zevio
Stella Zevio, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
28/09/2020    12:30 - 13:30
Résumé :
Qui assigner au comité de lecture de la conférence que j'organise ? Au comité de thèse de mon doctorant ? Qui sont les membres éminents et les publications phares de mon domaine de recherche ? Suis-je un chercheur émérite ? Qui dois-je citer et avec qui dois-je collaborer pour espérer faire partie des membres éminents de la communauté scientifique et améliorer ma réputation ? Afin de répondre à ces problématiques essentielles, nous proposons une méthode de recherche d’experts à partir de publications scientifiques combinant annotation sémantique à l’aide d’une ontologie et fouille de motifs dans les coeurs de graphes attribués.
LOVE 24/09/2020 Intersection Type Distributors, par Federico Olimpieri
Federico Olimpieri, Aix-Marseille Université  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (code d'accès: 749983)
24/09/2020    10:00 - 11:00
Résumé :
Building on previous works, we present a general method to define proof relevant intersection type semantics for pure lambda calculus. We argue that the bicategory of distributors is an appropriate categorical framework for this kind of semantics. We first introduce a class of 2-monads whose algebras are monoidal categories modelling resource management, following Marsden-Zwardt's approach. We show how these monadic constructions determine Kleisli bicategories over the bicategory of distributors and we give a sufficient condition for cartesian closedness. We define a family of non-extentional models for pure lambda calculus. We then prove that the interpretation of lambda terms induced by these models can be concretely described via intersection type systems. The intersection constructor corresponds to the particular tensor product given by the considered free monadic construction.
LOVE 17/09/2020 All your base categories are belong to us: A syntactic model of presheaves in type theory, par Pierre-Marie Pédrot
Pierre-Marie Pédrot, INRIA  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (code d'accès: 749983)
17/09/2020    10:00 - 11:00
Résumé :
Presheaves are a staple categorical structure, which naturally arises in a wide variety of situations. In the realm of logic, they are often used as a model factory. Indeed, presheaves over some base category will result in a topos, whose contents can be fine-tuned by carefully picking the base category. As computer scientists, though, we have learnt that there are even better logical systems than toposes: dependent type theories! Through the Curry-Howard mirror, they are also full-blown functional programming languages that actually compute. This begs the following question: is it possible to build the type-theoretic equivalent of presheaves, while retaining the good computational properties of our dependent programming languages? We will see that strikingly enough, presheaves can already be presented as computational objects to some extent, except for the annoying fact that they do not obey the right conversion rules! A proper account of type-theoretic presheaves will require a coming-of-age journey through the world of effectful program semantics, using fine and modern tools such as call-by-push-value, dependent parametricity and strict equality. In the end, we will formulate an alternative presentation of presheaves in type theory, but which is still equivalent to its standard categorical counterpart when viewed from the static world of sets. As an application, we will use them to extend dependent type theory with new effective logical principles.
LOVE 18/06/2020 SSAFire, a Monadic Gated SSA representation and its optimizations, par Thomas Rubiano
Thomas Rubiano, INRIA  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24
18/06/2020    10:00 - 11:30
Résumé :
I'll present SSAFire, a variant of the monadic gated Static Single Assignment form, where programs are represented by dependency graphs, rather than control-flow graphs. Its referential transparency makes it useful to implement several global program optimizations as simple graph transformations that can be justified using symbolic and local reasoning.
LOVE 11/06/2020 Exploiting Pointer Analysis in Memory Models for Deductive Verification, par Mihaela Sighireanu
Mihaela Sighireanu, University Paris Diderot, IRIF  
https://bbb.lipn.univ-paris13.fr/b/ari-uht-t3u
11/06/2020    14:00 - 15:00
Résumé :
Cooperation between verification methods is crucial to tackle the challenging problem of software verification. I'll present such a collaboration involving static analyzers doing pointer analysis and a deductive verification method based on first order logic. The idea is to exploit the result of pointer analysis in order to provide a memory model to the deductive verification that captures precisely the disjointedness of regions in the program memory. The accuracy obtained in the memory model is essential for shortening aliasing annotations and improve the results of automated solvers. This cooperation has been implemented inside the Frama-C platform.
RCLN 08/06/2020 Generating Referring Expressions from RDF Knowledge Graphs for Data Linking , par Armita Khajeh-Nassiri
Armita Khajeh-Nassiri  
Virtuel sur Jitsi: https://jitsi.lipn.univ-paris13.fr/RDFKGforDataLinking
08/06/2020    15:00 - 16:00
Résumé :
In a knowledge graph, a referring [removed]RE) is a logical formula that can uniquely identify an entity. We propose a novel approach for discovering REs that are valid within a class of a knowledge graph. There can potentially exist many REs for each entity, hence we have focused on those descriptions that are 1) minimal 2) diverse and that 3) can not be found by instantiating the keys. As an application, we study the data linking problem that, given two knowledge graphs G1 and G2, finds the possible links between the entities of G1 and G2. We show that REs can drastically improve the quality of data linking. Rejoindre la réunion?: https://jitsi.lipn.univ-paris13.fr/RDFKGforDataLinking
LOVE 04/06/2020 Logic Beyond Formulas: A Proof System on Graphs, par Matteo Acclavio
Matteo Acclavio, SaToSS, Université du Luxembourg  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (access code: 638888)
04/06/2020    10:00 - 11:30
Résumé :
In proof theory, proof systems usually operate on formulas, that is, objects characterized by an underlying tree structure. The aim of this talk is to define a proof system operating on general (undirected) graphs instead of formulas. We start from the correspondence between formulas and cographs, i.e. graphs containing no chordless paths of length 3. As a consequence of considering general graphs, we can no longer use the standard proof theoretical methods relying on the tree structure of formulas: for instance, we are not able to identify the main connective of a formula. Thanks to graphs modular decomposition and some techniques from deep inference, we are able to define a proof system with admissible cut and which is a conservative extension of MLL with mix. This talk is based on a joint work with Ross Horne and Lutz Strassburger.
LOVE 28/05/2020 A cellular Howe theorem, par Tom Hirschowitz
Tom Hirschowitz, CNRS & Université Savoie Mont Blanc  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (access code: 638888)
28/05/2020    11:00 - 12:30
Résumé :
We introduce a categorical framework for operational semantics, in which we define substitution-closed bisimilarity, an abstract analogue of the open extension of Abramsky's applicative bisimilarity. We furthermore prove a congruence theorem for substitution-closed bisimilarity, following Howe's method. We finally demonstrate that the framework covers the call-by-name and call-by-value variants of lambda-calculus in big-step style. As an intermediate result, we generalise the standard framework of Fiore et al. for syntax with variable binding to the skew-monoidal case. This is joint work with Peio Borthelle and Ambroise Lafont.
LOVE 19/05/2020 Focusing on lambda-calculus equivalence, par Gabriel Scherer
Gabriel Scherer, INRIA  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (access code: 638888)
19/05/2020    15:30 - 17:00
Résumé :
In this overview talk we will show how the logical technique of focusing can be applied to better understand program equivalence in the simply-typed lambda-calculus with datatypes (in particular sums and the empty type). The talk will not assume familiarity with focusing, and introduce it in the context of propositional intuitionistic logic. We will then present a focused presentation of the (normal forms of the) lambda-calculus. If time allow, we will then introduce the "saturated" normal forms, a stronger restriction that we used in https://arxiv.org/abs/1610.01213 (2017) to decide equivalence of simply-typed lambda-terms with sums and the empty type.
LOVE 07/05/2020 Implicit automata in typed lambda-calculi, par Nguyen Lê Thành Dung
Nguyen Lê Thành Dung, LIPN, Université Sorbonne Paris Nord  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (access code: 638888)
07/05/2020    10:00 - 11:30
Résumé :
We show that various classes of languages and functions from automata theory can be equivalently defined using lambda-calculi with substructural types. For instance, we characterize regular string-to-string functions with affine types, and star-free languages with non-commutative types. These results have few direct precedents, but they are analogous to the field of implicit computational complexity, except with automata instead of complexity classes. Our starting point is the little-known fact that the predicates definable over Church-encoded strings in the simply typed lambda-calculus are exactly the regular languages (Hillebrand & Kanellakis, LICS'96). More recently, similar ideas have played a prominent role in higher-order model checking. This is joint work with Pierre Pradic (University of Oxford).
LOVE 30/04/2020 Taylor Subsumes Scott, Berry, Kahn and Plotkin, par Davide Barbarossa
Davide Barbarossa, LIPN  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (access code: 638888)
30/04/2020    10:00 - 11:30
Résumé :
The speculative ambition of replacing the old theory of program approximation based on syntactic continuity with the theory of resource consumption based on Taylor expansion and originating from the differential lambda-calculus is nowadays at hand. Using this resource sensitive theory, we provide simple proofs of important results in lambda-calculus that are usually demonstrated by exploiting Scott's continuity, Berry's stability or Kahn and Plotkin's sequentiality theory. A paradigmatic example is given by the Perpendicular Lines Lemma for the Böhm tree semantics, which is proved here simply by induction, but relying on the main properties of resource approximants: strong normalization, confluence and linearity.
AOC 23/04/2020 Méthodes primal-dual avec la programmation linéaire des configurations, par Nguyen Kim Thang
Nguyen Kim Thang, Université d'Evry  
Salle B107, bâtiment B, Université de Villetaneuse
23/04/2020    10:30 - 11:30
Résumé :
Primal-duale est une méthode élégante et puissante en optimisation et en algorithmique. La méthode consiste à établir de manière interactive des solutions primals et duales, puis un algorithme, ainsi que son analyse, sont guidés naturellement par l'interaction primal-duale. Dans cet exposé, je vais présenter les approches primal-dual comme techniques unifiées afin d'étudier et de développer les algorithmes les domaines de la théorie des jeux algorithmiques et de l'algorithmique en ligne.
LOVE 23/04/2020 The Complexity of Interaction Abstract Machines, par Gabriele Vanoni
Gabriele Vanoni, Università di Bologna  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (access code: 638888)
23/04/2020    10:00 - 11:30
Résumé :
Geometry of Interaction (GOI) is a semantic framework describing the dynamics of cut-elimination in the Multiplicative Exponential fragment of Linear Logic (MELL). It has been formulated in many ways, from operator algebras to traced symmetrical monoidal categories. Remarkably, some of these formulations, in particular Context Semantics by Gonthier et al. led to the introduction of compilation techniques (Mackie '95) and abstract machines for higher-order functional languages (Danos and Regnier '99). However, these machines were always based on a proof-net representation of programs, via the so-called Girard translation. We introduce an abstract machine in the spirit of GOI based directly on the ?-calculus, without any explicit use of proof-nets. We prove soundness and adequacy, and we derive in our framework an optimization already presented by Danos and Regnier. We complete our study with a complexity analysis of those machines.
A3 16/04/2020 Décomposition et recherche Monte Carlo en General Game Playing, par Nicolas Jouandeau
Nicolas Jouandeau, Université Paris 8  
Salle B107, bâtiment B, Université de Villetaneuse
16/04/2020    12:15 - 13:45
Résumé :
Les jeux permettent de définir des problèmes non triviaux dans un cadre fini et maîtrisé, et offrent de fait un cadre intéressant pour l’étude des algorithmes de décision. Pour réduire l'influence de connaissances expertes spécifiques à un jeu et stimuler une analyse logique des problèmes, le General Game Playing (GGP) propose de jouer à des jeux inconnus en partant uniquement de la description logique de leurs règles. Dans ce contexte, nous proposons deux méthodes générales de décomposition des jeux décrits en Game Description Language (GDL), l'une s’appuyant sur une analyse logique des règles et l'autre sur une analyse statistique d’informations collectées pendant des simulations. Enfin nous présentons une variation de la méthode Monte Carlo Tree Search exploitant ces décompositions dans un joueur GGP et permettant de résoudre simplement certains jeux.
LOVE 16/04/2020 Automatic Differentiation in PCF, par Damiano Mazza
Damiano Mazza, LIPN, CNRS & Université Paris 13  
https://bbb.lipn.univ-paris13.fr/b/sei-eer-t24 (access code: 638888)
16/04/2020    10:00 - 11:00
Résumé :
Automatic differentiation (AD) is the science of efficiently computing the derivative (or gradient, or Jacobian) of functions specified by computer programs. It is a fundamental tool in several fields, most notably machine learning, where it is the key for training deep neural networks. Albeit AD techniques traditionally focus on a restricted class of programs, namely first-order straight-line programs, the rise of so-called differentiable programming in recent years has called for the need of applying AD to complex code, containing all sorts of control flow operators and higher-order combinators. In this talk, I will discuss the extension of AD algorithms to PCF, a(n idealized) purely functional programming language. We will first consider the simply-typed lambda-calculus, showing in particular how linear negation is related to reverse mode AD (aka backpropagation), and then see how the extra features of PCF, namely full recursion and conditionals, may be dealt with, stressing the difficulties posed by the latter. [Joint work with Aloïs Brunel (Deepomatic) and Michele Pagani (IRIF, Université de Paris)]
AOC 26/03/2020 Multi-period Hub Location Problem with Serial Demands: A Case Study of Humanitarian Aids Distribution in Lebanon, par Shahin Gelareh
Shahin Gelareh, Université dÂ’Artois  
Salle B107, bâtiment B, Université de Villetaneuse
26/03/2020    10:30 - 11:30
Résumé :
We address the problem of humanitarian aids distribution across refugee camps in war-ridden areas from a network design perspective. We show that the problem can be modeled as a variant of multi-period hub location problem with a particular demand pattern resulted by the user's behavior. The problem has been motivated by a case study of Lebanese experience in Syrian war refugee accommodation. We elaborate on the complexity and real-life constraints and, propose a compact formulation of a mathematical model of the problem. We then show that modeling the problem using a Benders paradigm drives O(n^3) variables of the original compact model unnecessary in addition to the constraints that are being projected out in a typical Benders decomposition. Additionally, we identify several classes of valid inequalities together with efficient separation procedures leading to a cut-and-Benders approach. Our extensive computational experiments on the case study with real data as well as randomly generated instances proves the performance of proposed solution methods.
LOVE 19/03/2020 REASONING ABOUT DYNAMIC NETWORKS OF INFINITE-STATE PROCESSES , par Mihaela Sighireanu
Mihaela Sighireanu , University Paris Diderot, IRIF  
Salle A303, Institut Galilée, Université Sorbonne Paris Nord
19/03/2020    10:00 - 11:00
Résumé :
We propose a framework for reasoning about unbounded dynamic networks of infinite-state processes. We propose Constrained Petri Nets (CPN) as generic models for these networks. They can be seen as Petri nets where tokens (representing occurrences of processes) are colored by values over some potentially infinite data domain such as integers, reals, etc. Furthermore, we define a logic, called CML (colored markings logic), for the description of CPN configurations. CML is a first-order logic over tokens allowing to reason about their locations and their colors. Both CPNs and CML are parametrized by a color logic allowing to express constraints on the colors (data) associated with tokens. We investigate the decidability of the satisfiability problem of CML and its applications in the verification of CPNs. We identify a fragment of CML for which the satisfiability problem is decidable (whenever it is the case for the underlying color logic), and which is closed under the computations of post and pre images for CPNs. These results can be used for several kinds of analysis such as invariance checking, pre-post condition reasoning, and bounded reachability analysis.
A3 16/03/2020 What (many kinds of) graphs can contribute to explainable machine learning, par Tiphaine Viard
Tiphaine Viard, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
16/03/2020    12:15 - 13:45
Résumé :
AI and machine learning are commonly described as "black boxes" that are efficient, but opaque. While complete opacity would be an exaggeration, it is true that many methods for explainability rely on forms of retro-engineering: we try to infer the model from its (partial, intermediary, final) results. These methods are typically based on large-scale, efficient matrix manipulation. Graphs and their extensions have shown to be visualisable and interpretable, even at large scales. In their classical formulation, they are also very similar to matrices, but also versatile: they can be directed, weighted, multilayered, temporal, etc. Each of those extensions giving rise to interesting algorithmic and data-driven questions. To date, few machine learning methods, harness the expressive power of graphs, in part due to the complexities of graph algorithms, typically having polynomial running times, which is incompatible with the scale of data at hand. However, the situation has changed: (i) the impact of AI on society makes it no longer acceptable to only favour efficiency despite explainability, and (ii) recent advances in algorithmic methods on graphs demonstrates that due to the nature of real-world graphs, even some NP-hard problems become tractable. The aim of this talk is to explore this avenue of research. We will discuss the state-of-the art as well as some past results in real-world (temporal) graph modeling and in explainability, and will then discuss some recent results on pattern mining on temporal graphs.
RCLN 10/02/2020 Attention is all I need, par José Angel Gonzalez-Barba
José Angel Gonzalez-Barba, Universidad Politécnica de Valencia  
Salle B107, bâtiment B, Université de Villetaneuse
10/02/2020    12:30 - 13:30
Document attaché
Résumé :
The use of attention mechanisms has been widespreaded along all the natural language processing tasks. These kind of mechanisms have increased the capacity of Deep Learning models allowing them to focus explicitly on the most discriminant relationships and properties for a given task. Recently, the Transformer model have replaced Convolutional and Recurrent neural networks in many NLP tasks, mainly due to its capability of modeling sequences, avoiding the sequential processing by using only attention mechanisms. In this talk I will speak about the application of the Transformer encoders to text classification in social media (Sentiment Analysis and Irony Detection in Twitter) and its application in a novel framework for extractive summarization. About the author: José Angel just finished his PhD and he is going to start a PostDoc in the group of Yoshua Bengio at the University of Montreal. His works on Spanish NLP have been very promising and he developed some state-of-the-art systems for sentiment analysis and summarization.
LOVE 30/01/2020 On the Versatility of Open Logical Relations: Continuity, Automatic Differentiation, and a Containment Theorem, par Raphaëlle Crubillé
Raphaëlle Crubillé, IMDEA  
Salle B107, bâtiment B, Université de Villetaneuse
30/01/2020    10:15 - 12:00
Résumé :
I will present a joint work with Barthe, Dal Lago and Gavazzo. Logical relations are one of the most powerful techniques in the theory of programming languages, and have been used exten- sively for proving properties of a variety of higher-order calculi. However, there are properties that cannot be immediately proved by means of log- ical relations, for instance program continuity and differentiability in higher-order languages extended with real-valued functions. Informally, the problem stems from the fact that these properties are naturally ex- pressed on terms of non-ground type (or, equivalently, on open terms of base type), and there is no apparent good definition for a base case (i.e. for closed terms of ground types). To overcome this issue, we introduce a generalization of the concept of a logical relation, which we dub open logi- cal relation, and prove that it can be fruitfully applied in several contexts in which the property of interest is about expressions of first-order type. Our setting is a simply-typed ?-calculus enriched with real numbers and real-valued first-order functions from a given set, such as the one of con- tinuous or differentiable functions. We first prove a containment theorem stating that for any such a collection of functions including projection functions and closed under function composition, any well-typed term of first-order type denotes a function belonging to that collection. Then, we show by way of open logical relations the correctness of the core of a recently published algorithm for forward automatic differentiation. Fi- nally, we define a refinement-based type system for local continuity in an extension of our calculus with conditionals, and prove the soundness of the type system using open logical relations.
LOVE 20/12/2019 Parametric schedulability analysis of a launcher flight control system under reactivity constraints, par Jawher Jerray
Jawher Jerray, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
20/12/2019    15:00 - 15:30
Résumé :
The next generation of space systems will have to achieve more and more complex missions. In order to master the development cost and duration of such systems, an alternative to a manual design is to automatically synthesize the main parameters of the system. In this work, we present an approach on the specific case of the scheduling of the flight control of a space launcher. The approach requires two successive steps: (1) the formalization of the problem to be solved in a parametric formal model and (2) the synthesis of the model parameters with a tool in an optimal way. We first describe the problematic of the scheduling of a launcher flight control, then we show how this problematic can be formalized with parametric stopwatch automata; we then present the results computed by IMITATOR. We compare the results to the ones obtained by other tools classically used in scheduling.
LOVE 20/12/2019 Concurrent Algorithms and Data Structures for Model Checking, par Jaco van de Pol
Jaco van de Pol, Aarhus University  
Salle B107, bâtiment B, Université de Villetaneuse
20/12/2019    14:00 - 15:00
Résumé :
Model checking is a successful method for checking properties on the state space of concurrent, reactive systems. Since it is based on exhaustive search, scaling the method to industrial systems has been a challenge since its conception. Research has focused on clever data structures and algorithms, to reduce the size of the state space or its representation; smart search heuristics, to reveal potential bugs and counterexamples early; and high-performance computing, to deploy the brute force processing power of clusters of compute-servers. The main challenge is to combine a brute force approach with clever algorithms: brute force alone (when implemented carefully) can bring a linear speedup in the number of processors. This is great, since it reduces model-checking times from days to minutes. On the other hand, proper algorithms and data structures can lead to exponential gains. Therefore, the parallelization bonus is only real if we manage to speedup clever algorithms. There are some obstacles: many linear-time graph algorithms depend on a depth-first exploration order, which is hard to parallelize. Examples include the detection of strongly connected components (SCC), and the nested depth-first-search (NDFS) algorithm. Both are used in model checking LTL properties. Symbolic representations, like binary decision diagrams (BDDs), reduce model checking to "pointer-chasing", leading to irregular memory-access patterns. This poses severe challenges on achieving actual speedup in (clusters of) modern multi-core computer architectures. This talk will present some of the solutions found over the last 10 years, leading to the high-performance model checker LTSmin. These include parallel NDFS (based on the PhD thesis of Alfons Laarman), the parallel detection of SCCs with concurrent Union-Find (based on the PhD thesis of Vincent Bloemen), and concurrent BDDs and other decision diagrams (based on the PhD thesis of Tom van Dijk). This functionality is provided in a specification-language agnostic manner, while exploiting the locality typical for a-synchronous distributed systems (based on the PhD thesis of Jeroen Meijer). Finally, I will sketch a perspective on moving forward from high-performance model checking to high-performance synthesis algorithms. Examples include parameter synthesis for stochastic and timed systems, and strategy synthesis for (stochastic and timed) games. The focus of the talk will be on a parallel algorithm for SCC decomposition
LOVE 17/12/2019 Parallel verification of concurrent systems using the Symbolic Observation Graph, par Hiba OUNI
Hiba OUNI, LIPN  
Salle A303
17/12/2019    12:30 - 13:30
Résumé :
Model checking is one of the major techniques used in formal verification. This technique takes a model of a system in question and decides whether it satisfies a given property or not. It is based on an exhaustive exploration of the state space of the system to be verified. Thus, the Model checking technique suffers from the state space explosion problem: it can happen that the verification process stops because of lack of time or space. One of the proposed solutions to tackle this problem is to parallelize the verification process. The use of distributed processing increases the speedup and scalability of model checking by exploiting the cumulative computational power and memory of a cluster of computers. Such approaches have been studied in various contexts leading to different proposed solutions for both symbolic and explicit model checking. In this talk, we shall present new model checking algorithms built on a parallel construction of the Symbolic Observation Graph: an abstraction of the state space graph that preserves Linear Temporal Logic (LTL). We implemented the proposed model checking algorithm within a C++ prototype and compared our preliminary results with the state of the art model checkers.
LOVE 14/11/2019 Formal Specification and Verification of Interactive Multimedia Scores, par Jaime Arias
Jaime Arias, LIPN  
Salle A303
14/11/2019    13:00 - 14:00
Résumé :
Interactive Scores (IS) is a formalism for composing and performing interactive multimedia scores with several applications in video games, live performance installations, and virtual museums. In this model, the composer defines the temporal organization of the score by asserting temporal relations (TRs) between temporal objects (TOs). At execution time, the performer may modify the start/stop times of the TOs by triggering interaction points while the system guarantees that all the TRs are satisfied. Implementations of IS and formal models of their behavior have already been proposed, but these do not provide usable means to reason about their properties. In this talk we presente a Timed Automata model that fully captures the temporal structure of IS during both composition and execution, and that makes it possible to reason about the written scores.
LOVE 07/11/2019 Journee CoGITARe, par Divers
Divers  
Salle B107, bâtiment B, Université de Villetaneuse
07/11/2019    10:00 - 17:00
Résumé :
Quatre exposés autour de l'inférence de types pour divers systèmes avec intersection et union. Exposants : Stephen Dolan, Giuseppe Castagna, Claude Stolze et Flavien Breuvart programme : https://lipn.univ-paris13.fr/~breuvart/CoGITARe/journee_inferencing_subtypes.php?lang=uk
LOVE 24/10/2019 Relative monads for relational reasoning, par Kenji Maillard
Kenji Maillard, Inria Paris  
Salle B107, bâtiment B, Université de Villetaneuse
24/10/2019    10:15 - 12:00
Résumé :
Relational verification is concerned with the problem of proving specifications relating either two runs of a single program, such as non-interference, or two different programs, for instance simulations or equivalences. Starting with Benton's Relational Hoare Logic for imperative programs, many varieties of relational program logics have been designed for specific classes of relational properties and effects. Focusing on the setting of monadic computations, we want to design a generic framework for relational program logics. In our quest to understand the federating principles underlying relational reasoning, we explain how basic core properties of relational program logics are suitably captured by relative monads, a generalization of monads that need not to be an endofunctor. Working "over the product", these relative monads establish a bridge between two computational monads, employed to encapsulate their relational specifications.
A3 17/10/2019 Explicative Data Analytics, par Martin Atzmüller
Martin Atzmüller, Tilburg University  
Salle B107, bâtiment B, Université de Villetaneuse
17/10/2019    14:00 - 16:00
Résumé :
Modeling and mining multi-modal and heterogeneous data is important in the context of analyzing knowledge and information processes in complex environments, e.g. for mining high dimensional and heterogeneous (sensor) data, the analysis of exceptional patterns, and complex network structures. For making sense of the data, explicative data analytics focuses on interpretable, transparent and explainable approaches, which is relevant for very many applications for analyzing data in science and industry. The talk presents according approaches for explicative data analytics incorporating methods from data science, machine learning, and human computing, exemplified by multi-modal sensor data analysis, pattern mining and graph analytics.
A3 03/10/2019 Optimal Transport for Machine Learning, par Bernard Kamsu-Foguem
Bernard Kamsu-Foguem, ENIT, Tarbes  
Salle B107, bâtiment B, Université de Villetaneuse
03/10/2019    12:15 - 13:45
Résumé :
Optimal transport defines a set of geometric tools with interesting properties (comparison and morphology of probability measurements) that make it particularly suitable for solving large scale artificial learning problems. Since probability distributions are omnipresent in Machine Learning (ML), whether theoretical or empirical, optimal transport can be useful in order to measure their separation or, even better, to be able to transform them at a lower cost. We will investigate techniques based on optimal transport in certain practical and theoretical contexts (text classification, multi-label classification and domain adaptation), to contribute to solving the associated Machine Learning (ML) problems.
RCLN 30/09/2019 Détection de la radicalisation sur les réseaux sociaux, par Frédérique Segond
Frédérique Segond, Inalco  
Salle C316
30/09/2019    12:30 - 13:30
Résumé :
Dans ce séminaire je présenterai le travail effectué dans le cadre du projet européen Saffron pour détecter la radicalisation sur les réseaux sociaux. Après avoir présenté la problématique et l’approche multidisciplinaire adoptée, je me focaliserai sur la description des modules d’analyse sémantique, en particulier sur le module d’extraction d’événements. J’illustrerai mon propos avec les difficultés rencontrées et parlerai de la difficulté d’évaluer un tel travail. Je conclurai en présentant les perspectives actuelles de ce travail par rapport à des projets en cours et à la plateforme MediaCentric développée chez Bertin IT.
MERCRED 25/09/2019 Brzozowski and Antimirov reordering derivatives, par Tarmo Uustalu
Tarmo Uustalu, Reykjavik / Tallinn  
Salle B107, bâtiment B, Université de Villetaneuse
25/09/2019    14:00 - 15:00
Résumé :
The Brzozowski and Antimirov derivatives are effective operations on regular expressions that calculate the (semantic) derivatives of a regular language. They yield constructions of finite deterministic and nondeterministic automata. In this talk, I show how these operations on regular expressions admit natural generalizations for trace closures of regular languages, which are languages obtained from a regular language by allowing some pairs of letters to commute. The automata from the Brzozowski and Antimirov reordering derivatives are generally not finite. But if the regular expression is star-connected or, more generally, if its language has uniform rank, they are. This is joint work with Hendrik Maarand. I will also give a short introduction to what we do in my groups in Tallinn and Reykjavik.
AOC 24/09/2019 Quelques problèmes d'optimisation dans les réseaux, par Cedric Bentz
Cedric Bentz, CNAM  
Salle B107, bâtiment B, Université de Villetaneuse
24/09/2019    12:30 - 13:30
Résumé :
J'évoquerai dans cet exposé quelques problèmes d'optimisation dans les réseaux auxquels je me suis intéressé, parfois en collaboration avec d'autres chercheurs, depuis quelques années. Dans certaines des variantes étudiées, les réseaux considérés peuvent être sujets aux pannes, ce qui peut nécessiter d'en tenir compte lors de la conception de tels réseaux. La première famille de problèmes étudiés tourne autour de généralisations du problème de multicoupe, prenant notamment en compte le fait que le bon fonctionnement d'un réseau peut être mis en cause même si seul un certain nombre des communications à assurer sont affectées, pour lesquelles des résultats de complexité paramétrée ont été récemment obtenus dans différents cas particuliers. La seconde famille tourne autour de problèmes de d-bloqueurs dans les graphes, dans lesquels on s'intéresse au nombre minimum de noeuds (sommets) ou de liens (arêtes) qui doivent tomber en panne pour que, intuitivement, le réseau descende en-dessous d'un certain seuil de fonctionnement. Plusieurs résultats de complexité notables ont ainsi été obtenus pour cette catégorie de problèmes, dont on ne sait souvent même pas déterminer facilement s'ils sont dans NP ou non. Enfin, la troisième et dernière famille tourne autour de problèmes d'arbres et de réseaux de Steiner, en présence de capacités, et dans certains cas de pannes. Concernant le problème d'arbre de Steiner avec capacités sur les arcs mais sans pannes, les résultats de complexité qui ont été obtenus permettent d'obtenir une caractérisation complète de la complexité de ce problème vis-à-vis de plusieurs paramètres. Concernant le problème de conception de réseaux de Steiner avec capacités et pannes, plusieurs formulations le modélisant, dont une formulation biniveau, ont été obtenues et comparées entre elles, de façon théorique comme expérimentale, et quelques inégalités permettant de les renforcer ont également été testées. Ces formulations peuvent toutes être adaptées au cas où l'on ajoute la possibilité de protéger un certain nombre de liens du réseau, mais un fait notable et pas nécessairement intuitif est que les relations entre les formulations diffèrent alors du cas précédent.
LOVE 19/09/2019 Unifying abstract and linear rewriting. , par Maxime
Maxime, Lucas  
Salle B107, bâtiment B, Université de Villetaneuse
19/09/2019    10:00 - 11:30
Résumé :
As opposed to abstract rewriting (where one studies a set of term up to some rewrite rules), linear rewriting consists in studying linear combinations of terms, up to some rewrite rules. However the naive definitions of termination does not work in this case. The usual solution consists in only considering well-formed rewriting steps. This however is not very satisfactory because usual rewriting lemmas cannot be applied directly to the linear case and have to be proven again. In this talk we present a formalism unifying the abstract and linear cases, based on the notion of reduction strategy. In this setting, we recover an analogue of Newman's Lemma, while weakening the termination hypothesis.
AOC 17/09/2019 Algorithmes auto-stabilisants, par Lélia Blin
Lélia Blin, Sorbonne Université LIP6  
Salle B107, bâtiment B, Université de Villetaneuse
17/09/2019    12:30 - 13:30
Résumé :
Dans le contexte des réseaux à grande échelle, la prise en compte des pannes est une nécessité. L'auto-stabilisation est une approche algorithmique de la tolérance aux pannes dans les systèmes distribués dont le but est de gérer la corruption de la mémoire des processeurs dues à des pannes transitoires. Plusieurs paramètres caractérisent l'efficacité d'un algorithme auto-stabilisant, dont en particulier (1) le temps pris par le système pour retourner dans une configuration légale suite à une corruption arbitraire de la mémoire de ses processeurs, et (2) l'espace mémoire utilisé par les processeurs pour exécuter l'algorithme. La minimisation de l'espace mémoire est motivée pas de nombreux aspects : existence de réseaux (tels que les réseaux de capteurs) offrant des espaces mémoires limités, la minimisation des échanges de données entre processeurs voisins, la limitation du stockage d'information afin de pouvoir utiliser des techniques de redondance, etc. Ce séminaire présentera l'auto-stabilisation au travers deux grands problèmes classiques : la construction d'arbres couvrants, notamment d'arbres couvrants de poids minimum, et l'election d'un leader. Il présentera en particulier les liens entre auto-stabilisation et les techniques de décision distribuée, incluant le calcul de bornes inférieures sur l'espace mémoire nécessaire à la résolution par des algorithmes auto-stabilisants des problèmes susmentionnés.
MERCRED 03/07/2019 The Robust Capacitated Facility Location Problem, par Marco Caserta
Marco Caserta, IU Business School  
Salle B107, bâtiment B, Université de Villetaneuse
03/07/2019    14:00 - 15:00
Résumé :
We present robust formulations for the capacitated facility location problems under demand uncertainty, both for the single-source and the multi-source variants. Robustness is defined over different uncertainty sets, i.e., the box, ellipsoidal, and polyhedral uncertainty sets. For each of these variants, we define the robust counterpart and we compare the results obtained through an extensive computational study. We test the effect of using different support sets and analyze the performance of each robust variant using scenario curves and price of robustness, among other measures.
AOC 02/07/2019 Aspects combinatoires du problème de l'UCP, par Pierre Fouilhoux
Pierre Fouilhoux, Lip6 - Paris 6 - Sorbonne Université  
Salle B107, bâtiment B, Université de Villetaneuse
02/07/2019    12:30 - 13:30
Résumé :
Le problème classique appelé Unit Commitment Problem (UCP) est le problème central de planification de production d'électricité. Le problème combinatoire au coeur du problème de l'UCP est appéle le Min-up/min-down UCP (MUCP). Il consiste à déterminer un plan de production sur un horizon de temps discrétisé, pour un ensemble de centrales électriques. A chaque pas de temps, la production totale doit répondre à une demande connue. Chaque unité doit satisfaire des contraintes de temps minimum de fonctionnement et d'arrêt. Elle correspond également à des coûts de production et de mise en marche. Nous étudions comment la complexité du MUCP évolue en fonction du nombre d'unités et de période. Nous montrons en particulier que ce probl&egrav e;me est NP-difficile au sens fort. Nous présentons plusieurs aspects polyédraux d'une formulation PLNE pour le MUCP en nous intéressant à la combinatoire liant la production des unités entre les pas de temps. Pour cette formulation, l'espace des solutions exploré par un algorithme de branchement contient de nombreuses solutions symétriques et sous-symétriques: deux solutions symétriques (resp. sous-symétriques) pouvant être obtenues l'une de l'autre par permutation de ses composantes (resp. d'une partie de ses composantes). Nous proposons deux techniques bien distinctes pour briser ces symétries et accélérer la résolution. La première technique s'appuie sur l'étude du polyèdre des permutations et sur un algorithme, dit de fixing, utilisé à chaque noeud de l'algorithme de branchement. La deuxième technique repose sur des inégalités linéaires et des variables additionnelles. Enfin, nous présentons plusieurs aspects prometteurs sur une nouvelle décomposition de Dantzig-Wolfe qui utilise plusieurs inégalités issues de notre étude polyèdrale. Travaux réalisés avec Pascale Bendotti et Cécile Rottner.
MERCRED 26/06/2019 La Maison des Maths d'Ispahan, par Amir Hashemi
Amir Hashemi, Université Technologique d'Ispahan  
Salle B107, bâtiment B, Université de Villetaneuse
26/06/2019    14:00 - 15:00
Résumé :
Dans une première partie, je présenterai le système de recherche et enseignement supérieur des universités iraniennes et discuterai de ses performances. Dans une seconde partie, je présenterai les missions et activités des Maison des Mathématiques iraniennes, dont la première a été établie en 1999 à Ispahan. Il s'agit donc d'un exposé non technique, plutôt meta-scientifique. Il sera accompagné de quelques gâteaux iraniens.
AOC 25/06/2019 Optimisation et Bicliques, par Denis Cornaz
Denis Cornaz, LAMSADE - Paris Dauphine  
Salle B107, bâtiment B, Université de Villetaneuse
25/06/2019    12:30 - 13:30
Résumé :
Un sous-graphe partiel, d'un graphe donné, est une biclique, de ce graphe, s'il est biparti complet. D'abord, nous passerons en revue des résultats classiques admettant des preuves élégantes, voir surprenantes, autour de cette notion. Ensuite, nous mènerons une étude structurelle, particulière à cette notion, permettant de mettre en œuvre une technique générale d'optimisation (branch-and-cut, -and-price). Nous terminerons par une conjecture récemment démontrée.
RCLN 24/06/2019 Identity links in knowledge graphs, par Nathalie Pernelle
Nathalie Pernelle, LRI, Université Paris Sud  
Salle B107, bâtiment B, Université de Villetaneuse
24/06/2019    16:00 - 17:00
Résumé :
As the Web of Data continues to grow, more and more large datasets – covering a wide range of topics and domains – are being added to the Linked Open Data (LOD) Cloud. It is inevitable that different datasets, most of which are developed independently of one another, will come to describe (aspects of) the same thing, but will do so by referring to that thing by different names. Thanks to identity links, datasets that have been constructed independently of one another are still able to make use of each other’s information. Many data linking approaches have been defined that are rule-based. Some of these approaches exploit ontology axioms such as keys. However, these axioms are rarely specified in the available ontologies. In this seminar, I will present two approaches that aim to discover more or less expressive keys in RDF data. Then, since data linking approaches do not obtain a 100% precision, I will show that some approaches can focus on detecting incorrect sameAs links or detect that they are valid only in a specified semantic context.
A3 19/06/2019 Data Explainability Through Linguistic Expression of Extracted Knowledge, par Marie-Jeanne Lesot
Marie-Jeanne Lesot, LIP6  
Salle B107, bâtiment B, Université de Villetaneuse
19/06/2019    12:15 - 13:30
Résumé :
The pervasive use of data science techniques extracts regularities from available data for different tasks, such as prediction, characterisation or structuring. A current challenge is to improve the legibility of the obtained results, so as to allow a data expert to understand better the content of the data. One way to address this challenge consists in presenting them in natural language, offering linguistic expressions which may be easier to interpret for the user. The choice of such a result formulation then has an impact on the machine learning techniques to be applied to the data. The talk will illustrate these questions for numerical data as well as for time series, respectively discussing the extraction of gradual itemsets, that linguistically express knowledge about feature covariations, and the extraction of periodicity-related linguistic summaries, using the specific quantifier “regularly”. In both cases, as well as for enriched contextual variants, the question is to define precisely the associated semantics and to design efficient extraction algorithms. The talk will also discuss the issue of measuring the relevance of the linguistic terms used to express the summaries, both with respect to the data structure, in case of linguistic variables, and with respect to the cognitive interpretation, in case of approximate numerical expressions.
LOVE 18/06/2019 Parametric schedulability analysis of a launcher flight control system under reactivity constraints, par Jawher Jerray
Jawher Jerray, Équipe LoVe, LIPN  
Salle A303
18/06/2019    13:00 - 13:30
Résumé :
The next generation of space systems will have to achieve more and more complex missions. In order to master the development cost and duration of such systems, an alternative to a manual design is to automatically synthesize the main parameters of the system. We present an approach on the specific case of the scheduling of the flight control of a space launcher. The approach requires two successive steps: (1) the formalization of the problem to be solved in a parametric formal model and (2) the synthesis of the model parameters with a tool. We describe the problematic of the scheduling of a launcher flight control, then we show how this problematic can be formalized with parametric stopwatch automata; we then present the results computed by IMITATOR.
LOVE 18/06/2019 Towards parallel verification of concurrent systems using the Symbolic Observation Graph, par Hiba OUNI
Hiba OUNI, Équipe LoVe, LIPN  
A303
18/06/2019    12:30 - 13:00
Résumé :
An efficient way to cope with the combinatorial explosion problem induced by the model checking process is to compute the Symbolic Observation Graph (SOG). Given a stutter-invariant event-based LT L formula ?, involving a subset of actions (called observable actions), the SOG is a condensed representation of the state space graph based on a symbolic encoding of the nodes (sets of states linked with unobservable actions) and an explicit representation of the edges (labelled with observable actions). It has the advantage to be much reduced comparing to the original state space graph while being equivalent with respect to stutter-invariant temporal properties (i.e., the original system satisfies ? if and only if the corresponding SOG satisfies ?). Aiming to go fu rther in the process of tackling the state space explosion problem, we propose in this paper to parallelize the construction of the SOG using a hybrid approach (distributed+shared memory). Doing so, we take advantage of the recent advances in computer hardware, by distributing the construction process over a large number of multi-core processors. We studied the performances of our new approach comparing to both distributed and shared memory approaches on one side, and to the sequential construction on the other side. The obtained results show that the proposed approach offers an interesting alternative allowing to completely exploit the available distributed architecture while offering significant speedup.
LOVE 13/06/2019 La logique du signe : Sémiologie structuraliste et typage par biorthogonalité pour l'analyse de corpus., par Juan Luis Gastaldi
Juan Luis Gastaldi, ETH Zürich, SPHERE Paris Diderot  
Salle B107, bâtiment B, Université de Villetaneuse
13/06/2019    10:30 - 12:30
Résumé :
Dans cette conférence, il s'agira de présenter le cadre théorique et conceptuel d'une recherche en cours associant le projet d'une théorie formelle du signe d'inspiration structuraliste à certains principes et ressources de la linguistique de corpus et de la logique linéaire. L'objectif de ce travail interdisciplinaire est d'inférer de façon non supervisée des structures grammaticales ou logiques émergentes pour tout système de signes donné sous la forme d'un corpus d'expressions. L'analyse formelle proposée se base sur une procédure de segmentation stratifiée et de typage par biorthogonalité, capable, en principe, de capturer des structures de tous les niveaux (phonologiques ou graphématiques, morphologiques, syntaxiques et sémantiques). D'un point de vue philosophique, la perspective adoptée implique une manière originale de rapporter la logique au langage et à d'autres systèmes naturels de signes.
MERCRED 05/06/2019 Alice au pays des frises et des pavages, par François Bergeron
François Bergeron, UQAM  
Salle B107, bâtiment B, Université de Villetaneuse
05/06/2019    14:00 - 15:00
Résumé :
La notion de frise d’entiers a été introduite dans les années 1970 par Conway et Coxeter. Une telle frise correspond à un nombre fini de bandes horizontales superposées d’entiers positifs (>0), bornées au-dessus et en dessous par des bandes de 1, avec une condition locale liant ces entiers. Plus explicitement on demande que ad-bc=1, pour toute configuration locale de a, b, c, et d en forme de «?diamant?» (a et d se suivent sur une même ligne, avec b et c respectivement juste au-dessus et en dessous). Conway et Coxeter ont souligné que cela force un phénomène de répétition cyclique horizontale; de là le terme de frise. Un autre aspect fascinant est qu’ il n’y a qu’un nombre fini de telles frises ayant un nombre fixé de lignes, et qu’elles sont énumérées par les nombres de Catalan. Après un survol de cette notion et de sujets reliés, nous allons en considérer diverses généralisations. En particulier, on établira des liens avec la formule de condensation de Dogdson (l’auteur d’Alice au pays des merveilles) pour un calcul récursif de déterminants.
LOVE 23/05/2019 Towards a Combinatorial Proof Theory, par Ben Ralph
Ben Ralph, Inria Saclay  
Salle B107, bâtiment B, Université de Villetaneuse
23/05/2019    14:00 - 16:00
Résumé :
Combinatorial proofs have been introduced by Hughes to give a ``syntax-free'' presentations for proofs in classical propositional logic. In a nutshell, a classical combinatorial proof consists of two parts: (i) a linear part, and (ii) a skew fibration. The linear part encodes a proof in multiplicative linear logic (MLL), whose conclusion is given represented in a cograph, while the skew fibration maps this linear cograph to the cograph of the conclusion of the whole proof. For deep inference proofs, this skew fibration corresponds exactly to a contraction-weakening derivation. Applying certain restrictions to these two rules leads to substructural logics and substructural proof theory. These proof theoretic restrictions correspond precisely to set-theoretic and graph-theoretic restrictions on the skew fibration, allowing us to characterise proof systems by their graph homomorphism class.
A3 23/05/2019 Universal and best approximation through Bayesian ARTMAP, par Lucian SASU
Lucian SASU, Transilvania University of Brasov (Romenia)  
Amphi Ampere
23/05/2019    14:00 - 15:30
Résumé :
Bayesian ARTMAP is an adaptive resonance-theory based model, which was extended to perform regression. The network is shown to have both universal and best approximation properties. The network architecture and learning algorithm are presented, along with sketches of proofs and open questions.
LOVE 23/05/2019 Rigid species and normal functors over groupoids , par Zeinab Galal
Zeinab Galal, IRIF  
Salle B107, bâtiment B, Université de Villetaneuse
23/05/2019    10:30 - 12:00
Résumé :
Species of structures were introduced by Joyal as a unified framework for the theory of generating series in enumerative combinatorics. Species are connected to Girard's normal functor semantics of ?-calculus where terms are interpreted as power series with sets as coefficients. Fiore et al. presented a generalised definition that both encompasses Joyal's species and constitutes a model of differential linear logic (DiLL). For generalised species of structures, types are interpreted as groupoids which provides the connection with combinatorics whereas they are interpeted as sets in Girard's normal functors. To investigate how these models interact, we show that all the interpretations of proofs in DiLL actually live in a smaller fragment of generalised species called rigid species. These species correspond to the concept of free groupoid actions which provides us with a notion of normal functors over groupoids and allows us to bridge the gap between species and normal functors.
MERCRED 22/05/2019 Theoretical and Applied Research in Machine Learning, par Lucian SASU
Lucian SASU, Transilvania University of Brasov, Roumanie  
Salle B107, bâtiment B, Université de Villetaneuse
22/05/2019    14:00 - 14:45
Résumé :
Some insights and experiences in theoretical and applied research are shared. The two worlds are quite different and complementary. The presentation exposes challenging topics in industry which can be addressed through ML, along with hints for researchers willing to join industrial R&D departments.
RCLN 17/04/2019 Résumé de texte translingue par compression, par José Manuel Torres-Moreno
José Manuel Torres-Moreno, LIA, U.Avignon  
Salle B107, bâtiment B, Université de Villetaneuse
17/04/2019    14:30 - 15:30
Résumé :
Le Résumé Translingue de Textes (RTT) vise à générer un résumé dans une langue autre que le document source. Plus précisément, le RTT consiste à analyser un document dans une langue source pour en extraire sa signification, puis à générer un résumé court, informatif et correct dans une langue cible. Ce processus peut être divisé en deux processus principaux : le résumé et la traduction. Processus souvent antagonistes. Nous avons développé un cadré expérimentale pour générer des résumés translingues de documents en anglais, français, portugais, espagnol vers {anglais, français}. Nous avons utilisé des applications du TALN (résumé par extraction, similarité de phrases, compression de phrases et fusion multi-phrases) et des approches neuronales pour construire nos modèles de RTT. Cette présentation sera ciblée sur les techniques et les résultats obtenus lors de nos expériences.
LOVE 16/04/2019 Run-time Monitoring Approach for Hardware Trojans Dectection, par Maha Naceur
Maha Naceur, Université Paris 13  
Salle A303, bâtiment A, Université de Villetaneuse
16/04/2019    12:30 - 13:30
Résumé :
TodayÂ’s integrated circuits are vulnerable to malicious activities and alterations such as Hardware Trojan Horses (HTH), which can alter the functioning of the circuit, either during design or fabrication. Run-time monitoring is a predominantly used technique to validate a design in industry. Formal veri?cation overcomes the weakness of exhaustive simulation by applying mathematical methodologies to prove design correctness in an automated way. The design is analysed only against their functional characteristics, and their parametric behavior are do not considered in order to analyze the effects of HTHs. In this work, we present a new approach which focuses upon a combined technique that integrates the best characteristics of both run-time monitoring and formal veri?cation methods to provide an effective design validation tool which uses assertions to automatically generate synthesizable monitors capable for detecting hardware trojan horses at runtime
RCLN 04/04/2019 Apprentissage automatique à partir de données complexes et dynamiques: Application aux données textuelles, par Parisa RASTIN
Parisa RASTIN, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
04/04/2019    13:30 - 14:30
Résumé :
Les données actuelles sont de plus en plus variées et complexes et il est en général nécessaire d’adapter les algorithmes d’analyse à chaque type de description des données. Les algorithmes d’apprentissage devraient cependant pouvoir être fonctionnels quel que soit le type des données et la métrique choisie. Nous présentons dans cet exposé un algorithme de clustering relationnel basée sur le système de Coordonnées Barycentriques pour homogénéiser la représentation des objets et des prototypes et traiter de grands ensembles de données complexes. Dans le système de Coordonnées Barycentriques, l’espace de représentation est défini par un ensemble unique de points de support choisis parmi les objets de la base d'apprentissage. La définition d’un prototype correspond au calcul d’un objet dans l’espace barycentrique. À partir de ces approches, nous proposons un algorithme d'apprentissage basé sur un réseau de neurones artificiel défini dans l'espace barycentrique, adapté aux flux de données textuelles et permettant un suivit dynamique de l'évolution des données au cours du temps. Nous présenterons une applications concrètes sur l’extraction de domaines d’intérêt extraits d’URLS à partir de trace de navigation en ligne.
LOVE 02/04/2019 Continuous models of computation: computability, complexity,, par Amaury Pouly
Amaury Pouly, IRIF  
Amphy Ampère
02/04/2019    14:00 - 15:30
Résumé :
Et un cours abstract si nécessaire: In 1941, Claude Shannon introduced a continuous-time analog model of computation, namely the General Purpose Analog Computer (GPAC), [which can be implemented in practice through the use of analog electronics or mechanical devices]. In this talk, we review some recents results on the link between the GPAC and Turing machines. We will also see a surprising result on universal polynomial differential equations. Finally, I will also mention some recent application of this work to show that chemical reaction networks are strongly Turing complete with the differential semantics.
LOVE 02/04/2019 Fault-tolerant matrix factorisation: a formal model and proof, par Daniel Torres
Daniel Torres, LIPN, Équipe LoVe  
Salle A303, bâtiment A, Université de Villetaneuse
02/04/2019    12:30 - 13:30
Résumé :
As the size of high performance systems grows, tolerating failures has become a major issue in parallel computing. In this paper, we present a Coloured Petri Net model for a fault tolerant matrix factorisation algorithm. On the model, we prove resiliency properties and completion of the algorithm in presence of failures whatever the size of the input. This illustrates how formal modelling and verification techniques can help designing proofs on distributed algorithms.
27/03/2019 Journée IA du LIPN
 
Amphi Euler
27/03/2019    09:00 - 18:00
Résumé :
Cette journée est organisée par le Laboratoire d’Informatique de Paris Nord LIPN a pour but de présenter des travaux en intelligence artificielle, soit réalisés par des chercheurs du LIPN soit réalisés par des chercheurs extérieurs aussi bien académiques qu’industriels. Cette journée aura lieu dans l’amphithéâtre Euler de l’institut Galilée. L’inscription est gratuite mais obligatoire.
LOVE 19/03/2019 The size-change principle for mixed induction and coinduction, par Pierre Hyvernat
Pierre Hyvernat, Lama (Université de Savoie, Chambéry)  
C 304
19/03/2019    14:00 - 16:00
Résumé :
The Size-Change Principle (SCP) is a simple algorithm giving a partial termination test for recursive definitions. If the language is lazy, it also gives (by duality) a partial productivity test for recursive functions involving coinductive types. This is what is used in Agda. Unfortunately, when inductive and coinductive types are nested, this is unsound: there are "well typed" and terminating recursive definitions producing terms in empty types. Such definitions make Agda inconsistant. Using ideas from L. Santocanale about circular proof and parity games, I'll show how the SCP can be used to check "totality" of recursive definitions. Besides the SCP, the main ingredient is a more informative of call-graph, and I'll sketch the proof of correctness by defining their semantics using power domains.
LOVE 19/03/2019 Modeling, Analysis and Design of Critical Systems, par Prof. Nejib Ben Hadj-Alouane
Prof. Nejib Ben Hadj-Alouane, National Engineering School of Tunis (ENIT) - OASIS Lab (Optimization, Analysis of Industrial Systems and Services)  
Salle A303, bâtiment A, Université de Villetaneuse
19/03/2019    12:30 - 13:30
Document attaché
Résumé :
Our work on critical systems targets a number of problem areas and applications, all requiring the development of models for analysis and verification, and tools for decision making. This talk focuses on four different problem areas, each requiring a different modeling framework and solution approach. We begin by exposing our new Petri nets modeling framework, Extended Timed Petri Nets (ETPN), useful in modeling a special class of hybrid systems, with a weak continuous component and a strong discrete one, encountered when dealing with modern man-made, embedded and real-time systems. We discuss a supervisory control problem based on this framework, along with other related issues dealing with model transformation and complexity. Our second problem addresses operating high-demand and high-performance virtualized data centers (DCs). We focus on the development of tools, based on operations research models and techniques, for the management of theses DCs, while striving to improve user applications performance and productivity. We focus on the problem of virtual machines (VMs) placement in geographically distributed data centers. We consider communicating VMs assigned to data centers that are connected via a backbone network. We aim to plan and optimize the placement of VMs in data centers so as to minimize the IP-traffic within the backbone network along with user service interruption. Our third problem deals with security and in computer systems, services and protocols. We use the property of opacity to capture secrecy-related problems. We focus on the development of an on-line method for the efficient verification of opacity in models based on automata. We also extend opacity with the introduction of a quantification measure. Our fourth problem deals with sensor networks and their use in precision agriculture. We show that the development of application-oriented infrastructure management techniques, such a routing protocols, is important for modern Fog/IoT networks. Throughout our talk we discuss several research perspectives and applications linked to modern technologies, such as IoT, Web Services and Cloud/Fog computing.
LOVE 19/03/2019 Inequalities between plethysm coefficients and Kronecker coefficients via geometric complexity theory, par Christian Ikenmeyer
Christian Ikenmeyer  
Salle B107, bâtiment B, Université de Villetaneuse
19/03/2019    10:30 - 12:00
Résumé :
Research on Kronecker coefficients and plethysms gained significant momentum when the topics were connected to geometric complexity theory, an approach towards computational complexity lower bounds via algebraic geometry and representation theory. Both types of coefficients appear independently in R. Stanley's list of "Positivity problems and conjectures in algebraic combinatorics". This talk is about a result that was obtained with geometric complexity theory as motivation, namely an inequality between rectangular Kronecker coefficients and plethysm coefficients. The proof interestingly uses insights from algebraic complexity theory. As far as we are aware, algebraic complexity theory has never been used before to prove an inequality between representation theoretic multiplicities. This is joint work with Greta Panova (Rectangular Kronecker coefficients and plethysms in geometric complexity theory, Adv Math 2017).
RCLN 11/03/2019 Structure Prediction Energy Network (SPEN) using Dual Decomposition on Dependency Parsing, par Xudong ZHANG
Xudong ZHANG, LIPN - RCLN  
Salle B107, bâtiment B, Université de Villetaneuse
11/03/2019    14:00 - 15:00
Résumé :
Dependency Parsing is one of the basic tasks in the field of Natural Language Processing (NLP). The goal is to find whether there exist a strong relationship between different words in a sentence. It can be used as the basic step of many NLP systems like question answering system. Solving a dependency parsing problem can be realized by a energy based network with the output of the neural network as a scalar (energy). The goal is to find the most compatible structure (a graph) with the input sentence and the most compatible structure is supposed to give the lowest energy for the neural network. As the structure of the sentence should be a tree (one root, every word has and only has one pa rent, no circle), to simplify the problem, people always construct a linear function corresponding to the structure that we want to find, i.e. we suppose different arcs are independent. However, this method may limit the capacity of the system to describe more complex relations. In this project, inspired by the idea of Structure Prediction Energy Network (SPEN), we construct a new neural network which is composed of two parts, i.e. local energy part and global energy part. We showed that it is possible to solve the problem with dual decomposition when we have a convex (non-linear) function for the global energy part together with the linear local energy part. As one part of my Phd thesis, this work is still ongoing.
A3 28/02/2019 Apprentissage statistique dans un contexte décentralisé et applications à la vision par ordinateur, par David Picard
David Picard, ENSEA Cergy-Pontoise  
Salle B107, bâtiment B, Université de Villetaneuse
28/02/2019    12:15 - 13:45
Résumé :
L'apprentissage statistique est de nos jours incontournable dans un certain nombre de tâches complexes, notamment dans le traitement des données multimédia comme la vision. Pour gagner en précision, des modèles de plus en plus complexes sont entraînés sur des volumes de données de plus en plus gros. Cependant, la répartition naturelle des données auprès des capteurs qui les ont crées laisse à penser qu'il serait préférable d'apprendre ces modèles sans collecter les données d'apprentissage auprès d'un calculateur central. Nous présentons dans cet exposé un paradigme d'apprentissage décentralisé asynchrone pour répondre à ce problème. Nous considérons le cas ou plusieurs calculateurs optimisent un modèle statistique à l'aide de données locales et coopèrent afin d'obtenir un modèle consensus. Nous montrons comment transposer des algorithmes d'apprentissage connus (k-means, PCA, SVM, deep learning) à ce paradigme, ainsi que des preuves de leur équivalence avec les versions centralisées. Enfin, nous montrons plusieurs exemples d'applications de ces modèles à des tâches de vision par ordinateur.
LOVE 27/02/2019 Monoides et algèbres de tris sur les groupes de coxeter, par Nicolas Thiéry
Nicolas Thiéry  
B311
27/02/2019    15:22 -
Résumé :

Le séminaire LCR accueille Nicolas Thiéry (Université Paris 11).

Le modèle combinatoire usuel pour décrire la 0-algèbre de Hecke H_n(0) (en type A) est de considérer l'algèbre (ou le monoïde) engendré par les opérateurs de tri-à-bulle élémentaires pi_i, i=1...n-1 définis comme suit: pi_i agit sur un mot de longueur n en triant les lettres en position i et i+1. Cette construction se généralise naturellement pour tout groupe de Coxeter fini.

En combinant ces opérateurs avec plusieurs variantes (tri croissant / décroissant / affine), nous construisons un certain nombre de monoïdes et algèbres. De manière étonnante en premier abord, ceux-ci se retrouvent munis d'une structure très riche, faisant intervenir la combinatoire des descentes (et une généralisation de celle-ci), les ordres usuels sur les groupes de Coxeter (Bruhat, permutohèdre gauche et droit), ainsi que de nouveaux ordres. Cette structure s'explique par de nombreuses connections avec la théorie des représentations, l'algèbre de Hecke affine, les fonctions symétriques, etc.

LOVE 27/02/2019 Une formalisation des actes de language en ludique (et quelques remarques générales sur l'utilisation de la logique en shs), par s et Samuel Tronçon
s et Samuel Tronçon  
B 311, LIPN
27/02/2019    15:22 -
Résumé :

Les séminaires LCR et RCLN accueillent Samuel Tronçon (Centre d'Epistémologie et d'Ergologie Comparative et Institut de Mathématiques de Luminy).

Nous proposons une formalisation des actes de langage dans le cadre formel de la Ludique. Nous définissons un acte de langage ludique (ALL) comme une structure exécutable apte à remplir certains tests, et dont l'interaction produit une modification du contexte. Notre modèle possède deux couches de représentation. La première, la plus primitive, est constituée par les interactions en contexte. Elle comprend donc les structures qui supportent l'acte de langage. La seconde, plus abstraite, est le résultat de catégorisations réalisées par les agents, sur la base des interactions réelles entre actes de langage et avec le contexte. Cette double articulation ouvre la voie à la prise en compte du caractère relatif des actes en fonction de sa structure, du contexte et de l'observateur.
LOVE 27/02/2019 (annulé pour cause de grève) une formalisation des actes de langage en ludique" (et quelques remarques générales sur l'utilisation de la logique en shs), par s et Samuel Tronçon
s et Samuel Tronçon  
B311
27/02/2019    15:22 -
Résumé :

(ANNULE pour cause de GREVE)

Les séminaires LCR et RCLN accueillent Samuel Tronçon (Institut de Mathématiques de Luminy et Paris 8).

Nous proposons une formalisation des actes de langage dans le cadre formel de la Ludique. Nous définissons un acte de langage ludique (ALL) comme une structure exécutable apte à remplir certains tests, et dont l'interaction produit une modification du contexte. Notre modèle possède deux couches de représentation. La première, la plus primitive, est constituée par les interactions en contexte. Elle comprend donc les structures qui supportent l'acte de langage. La seconde, plus abstraite, est le résultat de catégorisations réalisées par les agents, sur la base des interactions réelles entre actes de langage et avec le contexte. Cette double articulation ouvre la voie à la prise en compte du caractère relatif des actes en fonction de sa structure, du contexte et de l'observateur.
LOVE 27/02/2019 La plateforme why de vérification déductive de programmes c et java, par J.C. Filliâtre.
J.C. Filliâtre.  
B311
27/02/2019    15:22 -
Résumé :

Le séminaire LCR accueille Jean-Christophe Filliâtre (CNRS Université Paris 11).

Cet exposé présente la plateforme Why (http://why.lri.fr/), un ensemble de techniques et d'outils développés dans le projet ProVal pour la vérification de propriétés fonctionnelles de codes C et Java. La plateforme Why s'appuie sur plusieurs principes :
(1) la spécification des programmes par l'intermédiaire d'annotations dans le source, en utilisant des langages inspirés de JML ;
(2) un calcul de plus faibles préconditions reposant sur un modèle mémoire de type Burstall-Bornat raffiné par une analyse statique de séparation ; et enfin
(3) la possibilité d'utiliser un grand nombre d'outils de preuve existants, tant automatiques qu'interactifs, pour décharger les obligations de preuve.
LOVE 27/02/2019 (annulé pour cause de grève) monoides et algèbres de tris sur les groupes de coxeter, par N. Thiéry
N. Thiéry  
B311
27/02/2019    15:22 -
Résumé :

(ANNULE pour cause de GREVE)

Le séminaire LCR accueille Nicolas Thiéry (Université Paris 11).
(Travail commun avec Florent Hivert et Anne Schilling)

Le modèle combinatoire usuel pour décrire la 0-algèbre de Hecke H_n(0) (en type A) est de considérer l'algèbre (ou le monoïde) engendré par les opérateurs de tri-à-bulle élémentaires pi_i, i=1...n-1 définis comme suit: pi_i agit sur un mot de longueur n en triant les lettres en position i et i+1. Cette construction se généralise naturellement pour tout groupe de Coxeter fini.

En combinant ces opérateurs avec plusieurs variantes (tri croissant/décroissant/affine), nous construisons un certain nombre de monoïdes et algèbres. De manière étonnante en premier abord, ceux-ci se retrouvent munis d'une structure très riche, faisant intervenir la combinatoire des descentes, ainsi que les ordres usuels sur les groupes de Coxeter (Bruhat, permutohèdre gauche et droit). Cette structure s'explique en fait par de nombreuses connections avec la théorie des représentations, l'algèbre de Hecke affine, les fonctions symétriques, etc.
LOVE 27/02/2019 Fractional calculus: definitions, numerical methods and applications in control systems and multi-Scale processes, par Z. Odibat
Z. Odibat  
B311
27/02/2019    15:22 -
Résumé :

Le séminaire LCR accueille Zaid Odibat (Al-Balqa' Applied University, Jordan).

Recently, the fractional derivative has drawn much attention due to its wide application in various fields of physics and engineering. Fractional derivatives provide an excellent instrument for the description of memory and hereditary properties of various materials and processes. The main reason for using the integer-order models was the absence of solution methods for fractional differential equations. The real objects of using fractional-order models are that we have more degrees of freedom in the model and that a memory is included in the model. Fractional-order systems have an unlimited memory.

In this presentation, we will, first, introduce the most used definitions of fractional derivatives and their properties then we will highlight some comments about differential equations of fractional order. Second, we will give an overview of the recent analytical-approximate methods that are used to provide approximate solutions for nonlinear differential equations of fractional order. Finally, we will introduce some important areas of applications, where the use of fractional order models is expected to be very suitable and useful. Theses areas included the control systems and the multi-scale processes.
LOVE 27/02/2019 An introduction to size-Change termination analysis, par A. Ben-Amram
A. Ben-Amram  
B311
27/02/2019    15:22 -
Résumé :

Le séminaire LCR accueille Amir Ben-Amram(The Academic College of Tel-Aviv).

This talk describes an approach to the problem of determining whether a program terminates for all input data.

The basic idea of Size-Change Termination (SCT) is to prove that in any (hypothetic) infinite computation by the program, an infinite descent in some data arises. When the data considered are drawn from a well-founded set (typically the natural numbers), infinite descent is impossible, and the logical conclusion is: no actual computation path can be infinite.

The approach subsumes the usual methods of proving termination by observing that "something decreases" in each loop, e.g., lexicographic descent of a tuple of variables.

But how can the desired property be proven? The SCT technique relies on Size Change Graphs, a convenient abstraction of program behaviour. Using these graphs, it is possible to formulate the condition of interest in combinatorial terms, which helped to get several results, the first of which was that the property is decidable.

Subsequent work identified the complexity class of the problem (complete for PSPACE), investigated different algorithms (including efficient approximations), showed how to abstract different kinds of programs (functional, imperative, high-order, TRS...), and a lot more. This talk will be mostly introductory and include a brief exposition of results from the research of the speaker and his colleagues.

LOVE 27/02/2019 Réécriture, catégories d'ordre supérieur, et expressivité des modèles de calcul concurrent, par D. Mazza
D. Mazza  
B311
27/02/2019    15:22 -
Résumé :
Le séminaire LCR accueille Damiano Mazza (LIPN).

Un problème fondamental dans la comparaison de différents modèles du parallélisme et de la concurrence est celui de définir la notion de codage, ou de traduction. A ce jour, parmi toutes les notions universellement acceptées de codage entre modèles concurrents, il n'en existe aucune qui s'impose nettement sur les autres. Nous proposons d'étudier la notion de codage en partant de la vision du calcul comme réécriture, et en utilisant des notions venant de la théorie des catégories d'ordre supérieur et de la théorie des structures d'évenements de Winskel.
LOVE 27/02/2019 Descriptions algébriques et logiques de graphes finis, par B. Courcelle
B. Courcelle  
B311
27/02/2019    15:22 -
Résumé :

Le séminaire LCR accueille Bruno Courcelle (Labri).

De manière à étendre aux graphes les concepts fondamentaux de la Théorie des Langages Formels, on définit sur l'ensemble des graphes finis deux structures d'algèbre (de "magma" selon une terminologie obsolète) qui généralisent la structure de monoïde libre. On en déduit de manière immédiate des notions de reconnaissabilité (par congruences finies) et d'algébricité (par systèmes d'équations à points fixes) pour les graphes , et de nombreuses propriétés prouvables au niveau algébrique.

L'expression de propriétés de graphes en Logique du Second-Ordre Monadique permet de concrétiser la notion d'ensemble reconnaissable de graphes, de même que les automates finis concrétisent celle de langage reconnaissable (de mots ou de termes). Cette logique permet aussi d'étendre la notion de transduction rationnelle et de famille génératrice pour les 2 types d'ensembles équationnels considérés.

Il en résulte de nombreux résultats en particulier : algorithmes FPT pour ces propriétés, le paramètre étant la largeur arborescente ou "de clique", théorèmes de filtrage pour les ensembles équationnels de graphes et résultats de décidabilité associés, constructions effectives des mineurs exclus.
LOVE 27/02/2019 Calcul logique pour multiséquents, par C. Fouqueré
C. Fouqueré  
B311
27/02/2019    15:22 -
Résumé :

Le séminaire LCR accueille Christophe Fouqueré (LIPN).

Un Calcul logique gérant des multiséquents est présenté. Ce calcul est motivé par une réflexion sur l'évaluation paresseuse en programmation logique, ou encore la concurrence stricte et l'interférence. Le calcul introduit deux nouveaux connecteurs gérant la structure de multiséquents. C'est une extension conservative de la Logique Linéaire, permettant l'élimination des coupures. On proposera une sémantique des phases. Si le temps le permet, on évoquera des extensions du calcul.
LOVE 27/02/2019 Fonctions parfaitement non linéaires et actions de groupe, par L. Poinsot
L. Poinsot  
B311
27/02/2019    15:22 -
Résumé :

Le séminaire LCR accueille Laurent Poinsot (LIPN).

Les boîtes-S des procédés de chiffrement (à clef secrète) par blocs itéré sont notamment conçues pour résister aux attaques différentielle et linéaire. Ces cryptanalyses reposent sur la manière de combiner le texte clair et la clef. L'opération de combinaison traditionnellement employée est l'addition bit-à-bit de vecteurs binaires. Il existe d'autres façons de mélanger le clair et la clef, aussi dans cet exposé on se propose de remplacer l'addition par une action de groupe plus générale. On étudie alors l'attaque différentielle adaptée à cette nouvelle opération de combinaison ainsi que les boîtes-S qui lui opposent la meilleure résistance possible. On montre en particulier que l'on peut construire des fonctions robustes dans des cas où leurs homologues classiques (i.e. lorsque l'opération de combinaison est une addition binaire) n'existent pas.
LOVE 27/02/2019 Petit voyage au pays de la programmation logique inductive, par C. Rouveirol
C. Rouveirol  
B311
27/02/2019    15:22 -
Résumé :

Le séminaire LCR accueille Céline Rouveirol (LIPN).

Je présenterai une brève introduction à la Programmation Logique Inductive, qui s'intéresse aux modèles logique de l'apprentissage supervisé et plus largement à l'apprentissage supervisé dans les langages de concepts restrictions de la logique d'ordre un. Je motiverai ce type d'apprentissage, je détaillerai les modèles logiques les plus utilisés en Programmation Logique Inductive et quelques travaux fondateurs, pour enfin pointer vers quelques problématiques prometteuses.
LOVE 27/02/2019 Exponentials in ludics: how and at what price, par M. Basaldella
M. Basaldella  
B311
27/02/2019    15:22 -
Résumé :

Le séminaire LCR accueille Michele Basaldella (Università di Siena).

Ludics is a research project introduced by J-Y Girard in 2001 whose aim is to overcome the distinction Syntax/Semantics (of proofs) and it consists of a theory in which both sides deal with objects of the same nature, Design, which are basic artifacts of Ludics. They are manipulated by means of cut-elimination, conceived as the unique tool for testing properties inside the theory itself. Ludics also provides a (fully complete) Game Semantics for Multiplicative Additive Focalized Linear Logic. In this talk, we will show how to extend Ludics framework by adding exponential constructions in such a way to preserve the Ludics Theorems (in particular Separation Theorem). As we will see, our approach is closely related to AJM Game Semantics in the treatment of exponentials. We will also discuss the limits of our framework as well as its strength, namely the preservation of all isomorphisms involving exponentials, and the arising of a notion of non uniform exponential, both appearing in a rather natural way.
LOVE 27/02/2019 Modular construction of the symbolic observation graph, par L. Petrucci
L. Petrucci  
B311
27/02/2019    15:22 -
Résumé :

Le séminaire LCR accueille Laure Petrucci (LIPN).

Model checking for Linear Time Logic (LTL) is usually based on converting the (negation of a) property into a Büchi automaton, composing the automaton and the model, and finally checking for emptiness of the language of the composed system. The last step is the crucial stage of the verification process because of the state explosion problem. In this work, we present a solution which builds, in a modular way, an observation graph represented in a non-symbolic manner but where the nodes are essentially symbolic sets of states and the edges either labeled by events occurring in the formula or by synchronization actions between the system components. Due to the small number of events to be observed in a typical formula, this graph has a very moderate size and thus the time complexity for verification is negligible w.r.t. the time to build the observation graph. Experimental results show that our method outperforms both a non-modular generation of the symbolic graph and existing non-symbolic approaches (modular or not).
LOVE 27/02/2019 Mc-Sog: an ltl model checker based on symbolic observation graphs, par K. Klai
K. Klai  
B311
27/02/2019    15:22 -
Résumé :

Le séminaire LCR accueille Kais Klai (LIPN).

Model checking is a powerful and widespread technique for the verification of finite distributed systems. However, the main hindrance for wider application of this technique is the well-known state explosion problem. During the last two decades, numerous techniques have been proposed to cope with the state explosion problem in order to get a manageable state space. Among them, on-the-fly model-checking allows for generating only the "interesting" part of the model while symbolic model-checking aims at checking the property on a compact representation of the system by using Binary Decision Diagram (BDD) techniques. In this work, we propose a technique which combines these two approaches to check LTL\X state-based properties over finite systems. During the model checking process, only an abstraction of the state space of the system, namely the symbolic observation graph, is (possibly partially) explored. The building of such an abstraction is guided by the property to be checked and is equivalent to the original state space graph of the system w.r.t. LTL\X logic (i.e. the abstraction satisfies a given formula f iff the system satisfies f). Our technique was implemented for systems modeled by Petri nets and compared to an explicit model-checker as well as to a symbolic one (NuSMV) and the obtained results are very competitive.
LOVE 27/02/2019 Correctness of multiplicative additive proof structures is nl-Complete, par P. Jacobé de Naurois
P. Jacobé de Naurois  
B311
27/02/2019    15:22 -
Résumé :

Le séminaire LCR accueille Paulin Jacobé de Naurois (LIPN).

We revisit the correctness criterion for the multiplicative additive fragment of linear logic. We prove that deciding the correctness of corresponding proof structures is NL-complete. (Joint work with V. Mogbil).
LOVE 27/02/2019 L'interaction dure, par S. Lippi
S. Lippi  
B311
27/02/2019    15:22 -
Résumé :

Le séminaire LCR accueille Sylvain Lippi (I3S, Université de Nice).

Les systèmes durs, une sous-classe des réseaux d'interaction, se présentent sous la forme de systèmes de re-étiquetage de graphes fortement confluents. Nous présentons quelques traductions dans des sous-classes des systèmes durs et en déduisons quelques idées simples sur l'universalité. En particulier, nous donnons une traduction dans un système universel à 7 règles.
LOVE 27/02/2019 Réécriture de la géométrie, par Yves lafont
Yves lafont  
B107
27/02/2019    15:22 -
Résumé :

Le séminaire LCR accueille Yves lafont (IML - Université de la Méditerranée) en B107. Notez la salle inhabituelle.

Ce travail (en collaboration avec Pierre Rannou), vaguement inspiré par la recherche sur le calcul quantique, s'inscrit dans un programme de recherche plus vaste intitulé « Géométrie de la réécriture Ã‚». On représente les matrices orthogonales réelles (ou les isométries de [tex]$\mathbb{R}^n$[/tex]) par des « circuits orthogonaux Ã‚» construits avec deux types de portes : la symétrie (porte unaire) et les rotations (portes binaires). On obtient ainsi un système de réécriture de diagrammes qui est à la fois noetherien et confluent. La forme normale généralise la « décomposition d'Euler Ã‚». La confluence est évidente, mais l'étude des paires critiques conduit à une description axiomatique de la fonction permettant de passer d'une décomposition d'Euler à l'autre en dimension 3. En particulier, on retrouve l'« Ã©quation du tétraèdre Ã‚», aussi appelée équation de Zamolodchikov, bien connue des physiciens théoriciens.

Référence : Y. Lafont, Towards an Algebraic Theory of Boolean Circuits, Journal of Pure and Applied Algebra 184 (2-3), p. 257-310, Elsevier (2003).
LOVE 27/02/2019 Construction et maintenance d'entrepôts de données, par F. Boufares & co
F. Boufares & co  
B311
27/02/2019    15:22 -
Résumé :

Le séminaire LCR accueille pour une heure : Faouzi Boufares (LIPN), Sana Hamdoun (LIPN) et Mohamed Badri (CRIP5 - LIPN - Université Paris 5).

Les données nécessaires à des fins décisionnels sont de plus en plus complexes. Elles ont des formats hétérogènes et proviennent de sources distribuées. Elles peuvent être classées en trois catégories : les données structurées, les données semi-structurées et les données non-structurées. Dans cet exposé, nous présentons le processus d'intégration de données dans le but de construire un entrepôt dont les sources sont totalement hétérogènes. Nous proposons un cadre formel qui se base sur la définition d'un environnement d'intégration. Nous présentons également notre processus de maintenance d'entrepôt de données qui assure à la fois la mise à jour du contenu de l'entrepôt et l'actualisation des agrégats (indicateurs décisionnels) calculés sur les données de l'entrepôt.
LOVE 27/02/2019 Semantics for higher-Order quantum computation, par Benoît Valiron
Benoît Valiron  
B107
27/02/2019    15:22 -
Résumé :

Le séminaire LCR accueille Benoît Valiron (University of Ottawa).

We give a categorical semantics for a call-by-value linear, computational lambda calculus and discuss some steps towards a concrete model. Such a lambda calculus was used by Selinger and Valiron as the backbone of a functional programming language for quantum computation. One feature of this lambda calculus is its linear type system, which includes a duplicability operator "!" as in linear logic. Another main feature is its call-by-value reduction strategy, together with a side-effect to model probabilistic measurements.
LOVE 27/02/2019 From universal algebra and topology to lambda calculus and back, par Antonino Salibra
Antonino Salibra  
B311
27/02/2019    15:22 -
Résumé :

Le séminaire LCR accueille (en première partie d'une séance double) Antonino Salibra (Università Ca'Foscari di Venezia)

In this seminar we show how algebra and topology can be fruitfully applied to the operational semantics and to the model theory of the untyped lambda calculus. We explain the structure of the lattice of lambda theories (i.e., equational extensions of lambda calculus) and analyze one of the long-standing open problem of lambda calculus, regarding the existence of a topological model of the beta-eta lambda theory, where all Scott-continuous functions are representable.
LOVE 27/02/2019 Extraction de programmes classique dans le calcul des constructions, par Alexandre Miquel
Alexandre Miquel  
B311
27/02/2019    15:22 -
Résumé :

Le séminaire LCR accueille (en deuxième partie de cette séance double) Alexandre Miquel (PPS - Université Paris 7)

Dans cet exposé, je me propose de montrer que les techniques de réalisabilité classique introduites par Jean-Louis Krivine sont compatibles avec le Calcul des Constructions avec univers (CCw), et qu'elles permettent d'envisager un mécanisme d'extraction de programme à partir de preuves classiques (avec proof-irrelevance et axiome du choix) formalisées en Coq (dans la sorte Prop).

Pour cela, je commencerai par rappeler ce qu'est la réalisabilité classique au sens de Krivine (langage et modèles). Ensuite je montrerai comment étendre le modèle de réalisabilité de Krivine (initialement défini pour l'arithmétique du second ordre) à CCw, en utilisant une structure de Π-set réminiscente des structures de -set (Hyland, Longo, Moggi), de D-set (Streicher) et de λ-set (Altenkirch). Enfin, je présenterai un certain nombre de pistes pour étendre ce schéma d'extraction aux types inductifs (notamment les entiers) en utilisant des structures de données efficaces dans le langage cible (entiers binaires).

LOVE 27/02/2019 Le monoïde partiel libre, par Laurent Poinsot
Laurent Poinsot  
B311
27/02/2019    15:22 -
Résumé :

Le séminaire LCR accueille Laurent Poinsot (LIPN, Université Paris 13).

La structure de monoïde est fondamentale en informatique théorique, et plus précisément en combinatoire algébrique, puisqu'elle est reliée aux concepts de langages, d'automates, de séries formelles et d'algèbres de Lie combinatoires par exemple.

Un monoïde est un ensemble non vide muni d'une loi de composition interne associative et d'un élément neutre bilatère. De façon informelle, un monoïde partiel est un monoïde dont la loi de composition n'est que partiellement défini. Un monoïde à zéro est un monoïde (total) pourvu d'un élément distingué, le zéro, qui est absorbant pour sa loi de composition interne.

Dans cet exposé, après avoir effectué des rappels concernant ces différentes structures ainsi que des notions de théorie des catégories, je montre que les catégories des monoïdes à zéro et des monoïdes partiels sont essentiellement identiques (le zéro marque l'erreur d'un produit non défini), et qu'elles diposent d'un objet libre, à savoir, le monoïde partiel libre, généralisant en cela le résultat classique concernant l'existence du monoïde (total) libre.
LOVE 27/02/2019 Focalisation et ludique, par Alexis Saurin
Alexis Saurin  
B311
27/02/2019    15:22 -
Résumé :

Le 18 janvier 2010, à 15h30 en salle B311, le séminaire LCR accueille Alexis Saurin (PPS - INRIA ΠR2).

La propriété de Focalisation est l'un des résultats essentiels de la théorie de la démonstration de la logique linéaire, mettant en évidence le rôle essentiel de la polarité en logique. La Focalisation est la source de développements importants, allant de la programmation logique linéaire aux approches interactives de sémantiques de jeux.  La ludique, quant à elle, est un formalisme logique introduit par Girard il y a une dizaine d'années dont l'élément de base est la notion d'interaction.

L'exposé que je présenterai est le résultat d'une collaboration avec Basaldella et Terui, du RIMS à Kyoto. Terui a revisité récemment la théorie Ludique de Girard en y apportant de nouvelles perspectives, notamment selon l'aspect calculatoire, sous le nom de computational Ludics. Je présenterai une analyse interactive du théorème de focalisation menée dans le cadre de la Ludique de Terui.

J'expliquerai également les motivations de ce travail provenant de la remarque que la propriété de focalisation peut être vue comme reliée à des résultats de théorie de la complexité, notamment de compression de bande pour des Machines de Turing.
LOVE 27/02/2019 Mancoosi: reliable upgrades and quality assurance in foss distributions, par Stefano Zacchiroli
Stefano Zacchiroli  
B311
27/02/2019    15:22 -
Résumé :

Le 15 février 2010, à 15h30 en salle B311, le séminaire LCR accueille Stefano Zacchiroli (PPS).

FOSS (Free and Open Source Software) distributions are rather peculiar instances of component-based software infrastructures: they are developed rapidly and without "tight" central coordination, they are huge (tens of thousands of components), and their importance in the Internet computing infrastructure is growing.

Both the construction of a coherent collection of components (or packages), and the maintenance of installations based on these, raise difficult problems for distribution maintainers and system administrators. Distributions evolve rapidly by releasing new versions of packages and strive for increasingly high quality assurance requirements on their component collections. System upgrades may proceed on different paths depending on the current state of the system and the available software packages, and system administrators are faced with choices of upgrade paths (often unappropriately hidden), and with frequent upgrade failures.

The ongoing project Mancoosi (Managing the Complexity of the Open Source Infrastructure) aims to solve some of these problems. We will describe current and past work in the context of Mancoosi, as well as some future research directions.
LOVE 27/02/2019 Finite automata and regular fixed point formulas in mumall, par David Baelde
David Baelde  
B311
27/02/2019    15:22 -
Résumé :

Le 11 janvier 2010, à 15h30 en salle B311, le séminaire LCR accueille David Baelde (University of Minnesota, USA).

We present muMALL, an extension of multiplicative additive linear logic with least and greatest fixed points, and illustrate its expressiveness through the model-checking problem of non-deterministic finite automata inclusion.

We consider encoding automata as least fixed points in muMALL, and use its general induction scheme to reason about them. We provide a coinductive characterization of inclusion that yields a natural bridge to proof-theory. This yields a completeness theorem, but can also be generalized to the fragment of "regular formulas", obtaining new insights about inductive theorem proving and cyclic proofs in particular.
LOVE 27/02/2019 Une intégration de la sémantique lexicale à la sémantique compositionnelle montagovienne, par Christian Retoré
Christian Retoré  
B311
27/02/2019    15:22 -
Résumé :

Le 25 janvier 2010, à 15h30 en salle B311, le séminaire LCR accueille Christian Retoré (LaBRI -- Université de Bordeaux et CNRS, INRIA Bordeaux Sud-Ouest).

Les modèles formels de la sémantique du langage naturel sont relativement pauvres et méconnus si on les compare à ceux utilisés pour sa syntaxe. La sémantique de Montague, plutôt satisfaisante du point de vue formel, reste  incapable d'exprimer la polysémie ou les relations entre significations. A  l'autre extrême, les sémantiques lexicales sans structures, et en particulier sans structure  argumentale, n'ont pas de règles de composition pour calculer la signification d'entités composées. Nous avons proposé une notion de lexique sémantique  dans la lignée du lexique génératif de J. Pustejovsky comme un raffinement de la sémantique de R. Montague: en plus du lambda-terme usuel représentant la structure argument d'un mot, le lexique associe aussi des lambda-termes permettant au mot de changer son type et d'être relié à ses autres significations possibles. Le lambda-calcul du second ordre est utilisé pour anticiper les changements de type dépendant des types affectés aux autres mots. Ceci fournit un algorithme correct de calcul du sens d'expressions composées, que ce soit en utilisant les aspects pertinents du sens lors de la composition (qualia exploitation) ou en produisant exactement les sens correspondants à des coprédications possibles et en bloquant celles qui ne le sont pas --- ce que les modèles proposés jusqu'ici ne faisaient pas automatiquement.

On peut ainsi traiter d'exemples comme:
(1) un sourire amoureux et interrogatif (c'est l'auteur du sourire et non le sourire lui même qui est amoureux et  s'interroge)
(2) Le thon que nous  avons mangé hier était vif comme l'éclair et délicieux (coprédication quasi impossible entre l'animal et la nourriture)
(3) Copenhague est à la fois un port et une capitale cosmopolite (coprédication très acceptable entre le lieu, l'institution et les personnes)

Pour conclure nous procéderons à notre autocritique et expliquerons  comment des systèmes de types plus raffinés issus de la logique linéaire pourraient constituer un juste milieu entre l'approche présentée où types et termes sont trop indépendants et celle de N. Asher où les termes sont dictés par les types: linguistiquement est clair que seuls certains types permettent l'existence  de transformateurs de types, mais que leur existence dépend de la langue et de l'entrée lexicale considérée.

[Travail réalisé avec Christian Bassac (Lyon) et Bruno Mery (Bordeaux)]

Références bibliographiques:
Towards a Type-Theoretical Account of Lexical Semantics
Bassac C., Mery B., Retoré C.
Journal of Logic Language and Information (2009)
http://hal.archives-ouvertes.fr/docs/00/40/83/08/PDF/bassac-mery-retore-revised.pdf
LOVE 27/02/2019 Types et effets : des monades aux réseaux différentiels. 1ère partie : régions, stratification, monades, par Paolo Tranquilli
Paolo Tranquilli  
B311
27/02/2019    15:22 -
Résumé :

Le 1er février 2010, à 13h30 (attention à l'horaire inhabituel !) en salle B311, le séminaire LCR accueille Paolo Tranquilli (ENS Lyon).

Les systèmes de types et effets permettent une analyse statique des effets de bord des programmes. Par exemple, en considérant la mémoire comme un ensemble de régions, on peut annoter le type d'une procédure qui accède à des variables globales avec l'ensemble des régions affectées. Récemment, des systèmes de types et effets à régions stratifiées ont été proposés pour assurer la terminaison de lambda-calculs avec références (partagées entre plusieurs threads).

Mon exposé partira d'un autre outil utilisé pour traiter les effets : les monades de Moggi sont une notion de théorie catégorique qui peut être utilisée en théorie des types pour "enrober" les effets en gardant le système "pur". La monade d'état TA = S (SA) permet de modéliser l'accès à la mémoire ; en outre, en paramétrant S avec les régions, on peut facilement traduire le lambda-calcul (séquentiel) avec types et effets dans le lambda-calcul avec paires. On arrive alors à une justification purement logique de la stratification : son absence est en fait équivalente au besoin d'utiliser des types récursifs.

La traduction se transfère aisément aux réseaux de preuve de la logique linéaire, à partir de la traduction du lambda-calcul par valeur (la deuxième traduction de Girard). Les réseaux donnent une réduction parallèle du calcul qui en préserve la sémantique séquentielle. On pourra alors passer au travail en cours, qui mène à étendre cette traduction au calcul multi-threaded en utilisant les réseaux différentiels. La traduction, qui utilise les zones de communications déjà exploité pour le pi-calcul, donne une simulation, mais les réseaux obtenus ne sont pas nécessairement corrects comme dans le cas séquentiel. On est donc obligé soit de restreindre le calcul concurrent, soit d'étudier des extensions des réseaux ou des modifications de leur critère de correction.
LOVE 27/02/2019 Quelques thèmes de la théorie de la démonstration du xxe siècle, vus d'ajourd'hui, par Cycle de séminaires théorie de la démonstration, Abrusci-Vauzeilles
Cycle de séminaires théorie de la démonstration, Abrusci-Vauzeilles  
B311
27/02/2019    15:22 -
Résumé :

Dans la période de février à avril 2010, Vito Michele Abrusci (Università Roma Tre, professeur invité au LIPN) et Jacqueline Vauzeilles (LIPN) proposent un cycle de séminaires sur

Quelques thèmes de la théorie de la démonstration du XXe siècle, vus d'ajourd'hui

Le cycle est composé de quatre séances, ouvertes à tous, qui se tiendront au LIPN en salle B311, avec le calendrier suivant :
  • 15 février 2010, 13h30-15h : Hilbert
  • 22 février 2010, 13h30-16h30 : ordinaux et notations ordinales
  • 22 mars 2010, 13h30-16h30 : Gentzen et omega-logique
  • 19 avril 2010, 13h30-16h30 : beta-logique
LOVE 27/02/2019 Types et effets : des monades aux réseaux différentiels. 2ème partie, par Paolo Tranquilli
Paolo Tranquilli  
B311
27/02/2019    15:22 -
Résumé :

Le 1er mars 2010, à 13h30 (attention à l'horaire inhabituel !) en salle B311, le séminaire LCR accueille Paolo Tranquilli (ENS Lyon).

Les systèmes de types et effets permettent une analyse statique des effets de bord des programmes. Par exemple, en considérant la mémoire comme un ensemble de régions, on peut annoter le type d'une procédure qui accède à des variables globales avec l'ensemble des régions affectées. Récemment, des systèmes de types et effets à régions stratifiées ont été proposés pour assurer la terminaison de lambda-calculs avec références (partagées entre plusieurs threads).

Mon exposé partira d'un autre outil utilisé pour traiter les effets : les monades de Moggi sont une notion de théorie catégorique qui peut être utilisée en théorie des types pour "enrober" les effets en gardant le système "pur". La monade d'état TA = S  (S A) permet de modéliser l'accès à la mémoire ; en outre, en paramétrant S avec les régions, on peut facilement traduire le lambda-calcul (séquentiel) avec types et effets dans le lambda-calcul avec paires. On arrive alors à une justification purement logique de la stratification : son absence est en fait équivalente au besoin d'utiliser des types récursifs.

La traduction se transfère aisément aux réseaux de preuve de la logique linéaire, à partir de la traduction du lambda-calcul par valeur (la deuxième traduction de Girard). Les réseaux donnent une réduction parallèle du calcul qui en préserve la sémantique séquentielle. On pourra alors passer au travail en cours, qui mène à étendre cette traduction au calcul multi-threaded en utilisant les réseaux différentiels. La traduction, qui utilise les zones de communications déjà exploité pour le pi-calcul, donne une simulation, mais les réseaux obtenus ne sont pas nécessairement corrects comme dans le cas séquentiel. On est donc obligé soit de restreindre le calcul concurrent, soit d'étudier des extensions des réseaux ou des modifications de leur critère de correction.
LOVE 27/02/2019 Modélisation du protocole neoppod, par Sami Evangelista
Sami Evangelista  
B311
27/02/2019    15:22 -
Résumé :

Le 1er mars 2010, à 15h30 en salle B311, le séminaire LCR accueille Sami Evanglista (LIPN).
LOVE 27/02/2019 Jump from parallel to sequential proofs: exponentials, par Paolo Di Giamberardino
Paolo Di Giamberardino  
B311
27/02/2019    15:22 -
Résumé :

Le 26 avril 2010, à 13h30 en salle B311, le séminaire LCR accueille Paolo Di Giamberardino (LIPN).

In previous works, by importing ideas from game semantics (notably Faggian-Maurel-Curien's ludics nets), we defined a new class of multiplicative/additive polarized proof nets, called J-proof nets. The distinctive feature of J-proof nets with respect to other proof net syntaxes, is the possibility of representing proof nets which are partially sequentialized, by using jumps (that is, untyped extra edges) as sequentiality constraints. Starting from this result, in the present work we extend J-proof nets to take into account erasing (weakening) and duplication (contraction). More precisely, we show how using jumps makes possible to define nets where the usual nesting condition on boxes is relaxed, allowing a partial superposition of boxes. Moreover, we prove that, even in case of ''superposed'' boxes, reduction still enjoys confluence and strong normalization, using Gandy's method to prove strong normalization, following the work of Pagani and Tortora de Falco.
LOVE 27/02/2019 Un langage de programmation orienté interaction, par Jean-Louis Giavitto
Jean-Louis Giavitto  
B311
27/02/2019    15:22 -
Résumé :

Le 26 avril 2010, à 15h30 en salle B311, le séminaire LCR accueille Jean-Louis Giavitto (IBISC, CNRS-Université Evry).

Plusieurs formalismes informatiques tentent de capturer la notion d'interaction dans un système. MGS, un langage de programmation expérimental, est fondé sur la constatation que l'ensemble des interactions possibles s'organise suivant une structure topologique simple qui permet de spécifier la description du système et son évolution. Le style de programmation qui en résulte, la programmation spatiale, s'appuie sur des relations topologiques (connexité, bord, obstruction...) pour renouveler la notion de structure de données et a trouvé des applications effectives en algorithmique, en intelligence artificielle, dans la modélisation et la simulation en biologie des systèmes et dans la programmation des systèmes autonomes.

http://mgs.spatial-computing.org/
LOVE 27/02/2019 Game semantics and applications to compilation (3/3): A type system for hard real-time computation, par Dan Ghica
Dan Ghica, University of Birmingham  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 11:30
Résumé : 
We will examine a type system, suitable for higher-order functional programming languages with mutable state, which can automatically certify the timing of execution. The system is generally applicable to hard real-time computation and especially to the automatic synthesis of computational pipelines. We present the general typing rules, a categorical semantic model and a proof of coherence as well as a concrete programming language with a type inference algorithm and a concrete game-semantic model. [Joint work with Alex Smith]
LOVE 27/02/2019 Categorical models for simply typed resource calculi, par Giulio Manzonetto
Giulio Manzonetto  
D214
27/02/2019    15:22 -
Résumé :

Le 12 avril 2010, à 15h30 en salle D214 (attention à la salle inhabituelle !), le séminaire LCR accueille Giulio Manzonetto (LIPN).

In this talk we will present two resource sensitive lambda-calculi. The first one is the resource calculus, a non-lazy version of Boudol's lambda calculus with multiplicities.

In this calculus there are two kinds of resources: intuitionistic ones that can be erased and copied, and linear ones that must be used exactly once.

The second calculus is Ehrhard and Reignier's differential lambda calculus. In this calculus there are two kinds of applications: the usual application of lambda calculus and a linear application. This last one is useful to define a syntactical derivative operator on terms. We will see that these two calculi are strongly linked and that - in particular - the resource calculus can be easily translated into the differential one.

Subsequently, we will provide sufficient conditions on Blute-Cockett-Seely's Cartesian differential categories for being categorical models of the differential lambda calculus (and of the resource calculus by translation).

Finally, we will see that the concrete categories previously introduced as models of these calculi are instances of this abstract definition.
LOVE 27/02/2019 La sémantique relationnelle de la logique linéaire est-Elle injective?, par Daniel de Carvalho
Daniel de Carvalho  
D214
27/02/2019    15:22 -
Résumé :

Le 12 avril 2010, à 13h30 en salle D214 (attention à la salle inhabituelle !) le séminaire LCR accueille Daniel de Carvalho (LIPN).

Pour un certain fragment de la logique linéaire, la relation d'équivalence sur les preuves induite par l'élimination des coupures coïncide avec celle induite par le modèle relationnel basé sur les multi-ensembles.
LOVE 27/02/2019 Tour d'horizon de la programmation réactive, par Daniele Terreni
Daniele Terreni  
B311
27/02/2019    15:22 -
Résumé :

Le 10 mai 2010, à 15h30 en salle B311, le séminaire LCR accueille Daniele Terreni (LIPN).

Les systèmes réactifs sont des systèmes qui interagissent de façon intense avec leur environnement. Ils reçoivent des stimulations et doivent y réagir promptement. Selon la nature de l'environnement, leur réaction peut être soumise à des contraintes sur le temps d'exécution ou la quantité de mémoire utilisée. D'autre part, lorsque plusieurs interactions avec l'environnement sont possibles en même temps, ce qui est un cas typique, la nature de ces systèmes devient concurrente.

D'un point de vue mathématique, ces systèmes peuvent être décrits par des équations : les portions de l'état global sont des variables et ces variables obéissent à un ensemble d'équations récursives. Cet approche, très déclarative, paraît séduisante pour le programmeur : en spécifiant les invariants du système, il aura aussi décrit son implémentation.

Dans ce tour d'horizon, nous nous concentrerons sur les domaines d'application sans contraintes de temps ou de mémoire. Nous explorerons quelques langages conçus pour ces systèmes par des petits exemples de programmation. Nous essayerons de comprendre comment ces langages dépassent les limites des méthodes traditionnelles d'implémentation telles que les threads asynchrones ou les boucles évènementielles.
LOVE 27/02/2019 Church => scott = ptime: an application of resource sensitive realizability, par Aloïs Brunel
Aloïs Brunel  
B311
27/02/2019    15:22 -
Résumé :

Le 17 mai 2010, à 15h30 en salle B311, le séminaire LCR accueille Aloïs Brunel (ENS Lyon).

We introduce DIAL_lin, a dual variant of intuitionistic linear logic with second order quantifiers and type fixpoints, both restricted to purely linear formulas. Recasting an older result of Leivant and Marion, we give a characterization of the complexity class PTIME as the functions representable by a lambda-term of type 'Church' => 'Scott', where 'Church' is the type of usual Church binary words and 'Scott' the type of Scott words (a purely linear representation of words).

We will focus on the technique used to prove the soundess part of this result. It is a variant of the Dal Lago and Hofmann's realizability framework, which both gives meaning to the logic and allows us to bound the runtime of any typable lambda-term. We will discuss the possible extensions and simplification of this construction.
LOVE 27/02/2019 Graphes d'interaction, par Thomas Seiller
Thomas Seiller  
B311
27/02/2019    15:22 -
Résumé :

Le 31 mai 2010, à 15h30 en salle B311, le séminaire LCR accueille Thomas Seiller (IML, Aix-Marseille 2).

Je présenterai une sémantique localisée du fragment multiplicatif de la logique linéaire (MLL) où les preuves sont représentées par des graphes. Cette sémantique, inspirée des derniers travaux de J.-Y. Girard, se révèle être une version combinatoire de la géométrie de l'interaction dans le facteur hyperfini. Elle permet en particulier de mettre en rapport ces récents développements et les réseaux de preuves, les sémantiques de jeu ou la ludique. Je discuterai également d'une généralisation au fragment multiplicatif-additif de la logique linéaire (MALL).

LOVE 27/02/2019 How and why purely propositional separation logic is undecidable, par Max Kanovich
Max Kanovich  
B311
27/02/2019    15:22 -
Résumé :

Le 5 juillet 2010, à 15h30 en salle B311, le séminaire LCR accueille Max Kanovich (Queen Mary University of London).

Separation logic developed by Reynolds and O'Hearn has proven as an adequate formalism for the analysis of programs that manipulate memory (in the form of pointers, heaps, stacks, etc.). In addition to the standard propositional connectives, the most important feature of separation logic is its separating conjunction (A*B) which holds for a heap h iff h can be split into separate h1 and h2 so that A holds for h1 and B holds for h2.

Here our main focus is on the logic for concrete heap-like models of practical interest. Whatever concrete heap-like model H we take, it is undecidable whether a purely propositional formula A is valid in this model H. We also prove undecidability for a number of natural propositional systems (Boolean BI, Classical BI, etc.) developed on the road towards axiomatization of separation logic.

On top of that, our undecidability results for concrete heap-like models give new insights into the nature of decidable fragments of separation logic such as those given by Calcagno-Yang-O'Hearn(2001) and Berdine-Calcagno-O'Hearn(2004), as well as imposing boundaries on decidability.

To add a new exhibit to the Undecidability Zoo, we show the simplest undecidable purely propositional system, we call it Minimal BI, which employs only two conjunctions, that is * and &, and their two adjoint implications, respectively. (Neither negation nor `false' should be blamed for its undecidability)

(See also http://www.doc.ic.ac.uk/research/technicalreports/2010/)

This is joint work with James Brotherston (Imperial)
LOVE 27/02/2019 Linear dependent types and intensional expressivity, par Marco Gaboardi
Marco Gaboardi  
B311
27/02/2019    15:22 -
Résumé :

Le 20 septembre 2010, à 15h30 en salle B311, le séminaire LCR accueille Marco Gaboardi (Università di Bologna).

I present a work in progress, joint work with Ugo Dal Lago, aiming at providing a general framework for implicit computational complexity. By means of dependent types  and dependent modality in a linear setting we can formally reflect at the type level the program evaluation complexity. This fact allow us to obtain implicit characterizations of complexity classes that are complete in terms of programs, reducing the class membership problem to a corresponding constraint satisfaction problem.
LOVE 27/02/2019 Un calcul de coercitions qui prouve la normalisation forte de mlf, par Paolo Tranquilli
Paolo Tranquilli  
B311
27/02/2019    15:22 -
Résumé :

Le 15 novembre 2010, à 15h30 en salle B311, le séminaire LCR accueille Paolo Tranquilli (LIP, ENS Lyon).

Je présenterai un travail en collaboration avec Giulio Manzonetto qui montre la normalisation forte d'MLF par une simulation dans le système F. MLF est une extension conservative de ML qui permet de programmer tous le termes du système F à l'aide d'annotations partielles de type. Dans une première partie je vais décrire MLF, et notamment xMLF, sa variante explicite en style Church. Dans xMLF les relations d'instance des types sont explicitement notés par des entités nommées "instantiations" qui jouent en fait un rôle de coercitions et qui se réduisent de façon non triviale. Pour mieux raisonner sur ces aspects de xMLF on va le traduire dans une décoration du système F, le calcul de coercitions Fc, qui abstrait le mécanisme de coercition. On va donc présenter ce calcul et montrer que l'effacement des coercitions qui plonge Fc dans le lambda calcul ordinaire est une bisimulation faible. Finalement on va définir la traduction de xMLF dans Fc et utiliser la bisimulation pour montrer la normalisation forte des autres variantes de MLF aussi.
LOVE 27/02/2019 Full abstraction for resource calculus with tests, par Giulio Manzonetto
Giulio Manzonetto  
B311
27/02/2019    15:22 -
Résumé :

Le 22 novembre 2010, à 15h30 en salle B311, le séminaire LCR accueille Giulio Manzonetto (Nijmegen).

In this seminar we present a fully abstract model of the resource calculus "with tests".

We will first shortly recall the full resource calculus à la Tranquilli together with its relational model D, and we will define the problem of full-abstraction in this context.

We will then show that D is also a model of a resource calculus extended with two unary operators (similar to "raise" and "catch" of programming languages) and parallel composition |. With these operators (arising from differential proofnets) we can define "tests" that are able to check whether a term of the resource calculus converge.

We will then associate each element sigma in the interpretation of a term M with a context C_sigma converging on M and diverging on terms "different" from M. This will give us the full abstraction result.
LOVE 27/02/2019 Une critique de la notion d'information en biologie et un modèle de la complexité phénotypique au cours de l'évolution comme anti-Entropie, par Giuseppe Longo
Giuseppe Longo  
B311
27/02/2019    15:22 -
Résumé :

Le 29 novembre 2010, à 15h30 en salle B311, le séminaire LCR accueille Giuseppe Longo (LIENS, CNRS-ENS Paris).

The major observables in Physics are largely, if not exclusively, based on or derived from energy (conservation properties as symmetries, geodetic principles as least action principles...). Biology forced us to think in the novel terms of organization and, even, of inherited organization; an organization whose complexity grows along evolution and embryogenesis, against energy degradation in Physics (entropy production, also in non-isolated systems).

Then, with World War II, the age of coding, decoding and information started. Informatics, Information Theory and Cryptography became well defined scientific displines, with their own principles and remarkable applications. Can we borrow for the analysis of life phenomena any relevant principle or precise result from these scientific areas? A critique of the abuse of Information in Biology will be hinted.

Some recent work will be introduced on a quantification of biological (phenotypic) organization by a proper observable to Biology, anti-entropy. The idea will be derived by conceptual dualities w. r. to Quantum Physics, where the operatorial approach by Schrödinger to his famous equation will (dually) guide us towards an equational modelling of Goulds analysis of phenotypic complexity along Darwins Evolution and, if time allows, to some applications to embryogenesis.
LOVE 27/02/2019 Higher order processes and soft logic, par Simone Martini
Simone Martini  
B311
27/02/2019    15:22 -
Résumé :

Le 13 décembre 2010, à 15h30 en salle B311, le séminaire LCR accueille Simone Martini (Bologne, Professeur invité à Paris 13).

I will discuss an application of light/soft linear logic technology to restrict the higher order pi-calculus. In this restricted calculus any process terminates in polynomial time. While several interesting processes are expressible, more work is needed to understand a satisfactory way of describing "resource bounded" processes.
LOVE 27/02/2019 Functional programming in sublinear space, par Ugo Dal Lago
Ugo Dal Lago  
B311
27/02/2019    15:22 -
Résumé :

Le 20 décembre 2010, à 15h30 en salle B311, le séminaire LCR accueille Ugo Dal Lago (Bologne).

We consider the problem of functional programming with data in external memory, in particular as it appears in sublinear space computation. Writing programs with sublinear space usage often requires one to use special implementation techniques for otherwise easy tasks, e.g. one cannot compose functions directly for lack of space for the intermediate result, but must instead compute and recompute small parts of the intermediate result on demand. We study how the implementation of such techniques can be supported by functional programming languages.
LOVE 27/02/2019 Algebraic type systems, par Alejandro Di­az Caro
Alejandro Di­az Caro  
B311
27/02/2019    15:22 -
Résumé :

Le 17 janvier 2011, à 15h30 en salle B311, le séminaire LCR accueille Alejandro Di­az Caro (LIG, Grenoble).

In this talk I will present several extensions to the System F, for the sake of type the linear-algebraic lambda-calculus, a lambda-calculus enriched with a vectorial structure. The first type system is a straightforward extension of System F, which just types the calculus without any further adornment. The second one is a type system accounting for scalars, which can serve as a guarantee that the normal form of a term is of the form \sum a_i.t_i with \sum a_i=1. The following system includes "sums of types" reflecting that of the terms--showing that sums in the algebraic calculus behaves as a special kind of pairs. Eventually the last type system combines the previous two. We give counterexamples of why this kind of vectorial type system cannot be made in Curry style and show the clues of a future vectorial type system in Church style suitable to specialize the calculus into a quantum calculus.
LOVE 27/02/2019 On quantum lambda calculi, par Margherita Zorzi
Margherita Zorzi  
B311
27/02/2019    15:22 -
Résumé :

Le 7 février 2011, à 15h30 en salle B311, le séminaire LCR accueille Margherita Zorzi (Università di Verona).

In this talk we will introduce some theoretical results about quantum lambda calculi. Starting from a measurement-free calculus, called Q, we will show some "standard" properties (such as congruence and subject reduction) and some quantum properties, focusing on the expressive power and on the relationship with other quantum computational models.

Successively, we will consider Q*, an extension of Q with an explicit measurement operator, and we will propose a confluence result for reductions sequences regardless their niteness.

Finally, we will propose an ICC-like approach for the quantum setting: we will spend some words about a sub-calculus of Q, called SQ, which captures the three classes of the quantum polytime.
LOVE 27/02/2019 Quantum programming languages and logical approaches to quantum information theory, par Peter Selinger
Peter Selinger  
B311
27/02/2019    15:22 -
Résumé :

Dans la période du 7 au 17 février 2011, Peter Selinger (Dalhousie University, chercheur invité au LIPN) propose un cycle de séminaires sur

Quantum programming languages and logical approaches to quantum information theory

Le cycle est composé de quatre séances, ouvertes à tous, qui se tiendront au LIPN en salle B311, avec le calendrier suivant :
  • 7 février 2011, 13h30-15h
  • 10 février 2011, 10h-12h
  • 14 février 2011, 13h30-15h
  • 17 février 2011, 10h-12h
LOVE 27/02/2019 Von neumann algebras in physics by examples, par Pierre Martinetti
Pierre Martinetti  
B311
27/02/2019    15:22 -
Résumé :

Le 28 février 2011, à 15h30 en salle B311, le séminaire LCR accueille Pierre Martinetti (Università di Roma - Tor Vergata).

We will illustrate the importance of von Neumann algebras in physics, emphasizing in particular their role in the algebraic formulation of quantum field theory. We will illustrate by various examples how some characteristic properties of von Neumann algebra have a direct translation into properties of spacetime.
LOVE 27/02/2019 From cps to polarisation: a proof-Theoretic decomposition of delimited cps translations, par Guillaume Munch-Maccagnoni
Guillaume Munch-Maccagnoni  
B311
27/02/2019    15:22 -
Résumé :

Le 14 mars 2011, à 15h30 en salle B311, le séminaire LCR accueille Guillaume Munch-Maccagnoni (PPS, Paris 7).

The understanding of continuation-passing style (CPS) translations, an historical source of denotational semantics for programming languages, benefits from notions brought by linear logic, such as focalisation, polarities and the involutive negation. Here we aim to show how linear logic helps as well when continuations are delimited, i.e. return and can be composed, in the sense of Danvy and Filinski.

First we provide a polarised calculus with delimited control (first-class delimited continuations) which is, at the level of computation, a variant of Girard's polarised classical logic LC. It contains variants of delimited control calculi which spawned as answers to the question what order of evaluation can we consider with delimited control. Thus our polarised calculus is one answer which is unifying to some degree.

Subsequently we decompose the calculus through polarised linear logic. The only difference with non-delimited continuations is the use of specific exponentials, that account for the specific semantics of the target of delimited CPS translation, as well as annotations of type-and-effect systems.

As a by-product, we obtain an explanation of CPS translations through a factoring, each step of which accounts for distinct phenomena of CPS translations. Although the factoring also holds for non-delimited CPS translations, it did not appear in its entirety before.
LOVE 27/02/2019 Equivalence entre les analyses mwp et quasi-Interprétations, par Jean-Yves Moyen
Jean-Yves Moyen  
B311
27/02/2019    15:22 -
Résumé :

Le 21 mars 2011, à 15h30 en salle B311, le séminaire LCR accueille Jean-Yves Moyen (LIPN, Paris 13).

Les QI et l'analyse mwp sont deux techniques de complexité implicite pour caractériser Ptime. Les QI travaillent avec des programmes fonctionnels tandis que l'analyse mwp étudie des programmes impératifs.

Je montre, via une transformation de programmes, que bien qu'étant apparemment très différentes ces deux techniques sont moralement équivalentes et capables d'analyser les mêmes cas.
LOVE 27/02/2019 The geometry of multiplicatives and additives: interaction and orthogonality, par Etenne Duchesne
Etenne Duchesne  
B311
27/02/2019    15:22 -
Résumé :

Le 18 avril 2011, à 15h30 en salle B311, le séminaire LCR accueille Etienne Duchesne (LIF, Aix-Marseille 1).

We present a denotational semantics of multiplicative linear logic based on the geometry of interaction. In that semantics, we can define polymorphism using a construction similar to the one of history-free game semantics. We can also present the standard longtrip criterion of proof-nets as an orthogonality relation in the sense of Hyland and Schalk [HS03], and build a category of orthogonality which provides a fully complete model of MLL (without mix).

Besides we extend these constructions polymorphism and orthogonality, to the interpretation of additive connectives.
LOVE 27/02/2019 Estimation of the length of interactions in arena game semantics, par Pierre Clairambault
Pierre Clairambault  
B311
27/02/2019    15:22 -
Résumé :

Le 28 mars 2011, à 15h30 en salle B311, le séminaire LCR accueille Pierre Clairambault (Université de Bath, Royaume Uni).

We estimate the maximal length of interactions between strategies in HO/N game semantics, in the spirit of the work by Schwichtenberg and Beckmann for the length of reduction in simply typed lambda calculus. Because of the operational content of game semantics, the bounds presented here also apply to head linear reduction on lambda terms and to the execution of programs by abstract machines, including in presence of computational effects such as non-determinism or ground type references. The proof proceeds by extracting from the games model a combinatorial rewriting rule on trees of natural numbers, which can then be analysed independently of game semantics or lambda calculus

LOVE 27/02/2019 Theory of von neumann algebras and applications to physics, par Axel de Goursac
Axel de Goursac  
B311
27/02/2019    15:22 -
Résumé :

Le 11 avril 2011, à 15h30 en salle B311, le séminaire LCR accueille Axel de Goursac (Louvain).

We will review the basic theory of von Neumann algebras and see some applications to physics: algebraic quantum field theory, the CKM matrix.
LOVE 27/02/2019 Modèles de taylor pour la résolution du dilemme du fabricant de tables, par Erik Martin-Dorel
Erik Martin-Dorel  
B311
27/02/2019    15:22 -
Résumé :

Le 27 juin 2011, à 15h30 en salle B311, le séminaire LCR accueille Erik Martin-Dorel (LIP, ENS Lyon).

Le Dilemme du fabricant de tables est un problème d'Arithmétique des ordinateurs qui survient lorsqu'on veut implanter une fonction élémentaire (exp, log, sin, cos, arctan, etc.) avec arrondi correct. Exiger que les fonctions mathématiques soient correctement arrondies contribue à accroître la portabilité et la réutilisabilité des logiciels numériques, mais aussi permet de concevoir des algorithmes et des preuves de logiciels qui utilisent cette spécification.

Pour chaque fonction f considérée, la résolution de ce problème dépend de la connaissance des pires cas de f, qui sont les flottants dont l'image par f est très proche du milieu de deux flottants consécutifs. Deux algorithmes (Lefèvre et Stehlé-Lefèvre-Zimmermann) ont été conçus pour énumérer ces pires cas, mais leur temps de calcul avoisinant
plusieurs années-CPU, nous avons d'autant plus envie d'accroître la confiance que l'on peut avoir en leurs résultats.  C'est ce travail de certification qui constitue l'un des principaux buts du projet ANR TaMaDi (Table Maker's Dilemma) [1].

En particulier nous nous intéressons à la validation formelle de l'étape d'approximation polynomiale qui est commune aux deux algorithmes.  Pour ce faire, nous avons entrepris un travail de formalisation avec l'assistant de preuves Coq de ce qu'on appelle les Modèles de Taylor (un polynôme d'approximation + un reste certifié). Notre objectif est de pouvoir calculer des approximants certifiés avec une grande précision, à l'intérieur même de l'assistant de preuves. De plus, nous avons adopté une approche générique fondée sur des calculs par récurrence, vu que la plupart des fonctions élémentaires sont ce qu'on appelle des fonctions holonomes : elles satisfont une équation différentielle linéaire à coefficients polynomiaux, et par
conséquent leurs coefficients de Taylor vérifient une relation de récurrence.

Dans cet exposé, nous présenterons ainsi nos premiers développements réalisés en Coq [2], muni de l'extension SSReflect [3] et de la bibliothèque Coq-Interval [4], elle-même fondée sur la bibliothèque Flocq [5].

Ceci est un travail commun avec Nicolas Brisebarre, Mioara Joldes, Micaela Mayero, Jean-Michel Muller, Ioana Pasca, Laurence Rideau et Laurent Théry.

Liens :
[1] https://tamadiwiki.ens-lyon.fr/
[2] http://coq.inria.fr/
[3] http://ssr.msr-inria.inria.fr/
[4] http://www.lri.fr/~melquion/soft/coq-interval/
[5] http://flocq.gforge.inria.fr/
LOVE 27/02/2019 Programmation dans les diagrammes de cordes et logique tensorielle, par Paul-André Melliès
Paul-André Melliès  
Amphi Euler
27/02/2019    15:22 -
Résumé :

Dans la période du 4 au 13 juillet 2011, Paul-André Melliès (PPS, CNRS-Paris 7) propose un cycle de séminaires sur

Programmation dans les diagrammes de cordes et logique tensorielle

Le cycle est composé de quatre séances, ouvertes à tous, qui se tiendront à l'Institut Galilée et au LIPN, avec le calendrier suivant :
  • 4 juillet 2011, 14h-16h, amphi Euler (Institut Galilée)
  • 7 juillet 2011, 10h-12h, salle B311 (LIPN)
  • 11 juillet 2011, 14h-16h, salle B311 (LIPN)
  • 13 juillet 2011, 14h-16h, salle B311 (LIPN)
LOVE 27/02/2019 Programmation dans les diagrammes de cordes et logique tensorielle, par Paul-André Melliès
Paul-André Melliès  
B311
27/02/2019    15:22 -
Résumé :

Dans la période du 4 au 13 juillet 2011, Paul-André Melliès (PPS, CNRS-Paris 7) propose un cycle de séminaires sur

Programmation dans les diagrammes de cordes et logique tensorielle

Le cycle est composé de quatre séances, ouvertes à tous, qui se tiendront à l'Institut Galilée et au LIPN, avec le calendrier suivant :
  • 4 juillet 2011, 14h-16h, amphi Euler (Institut Galilée)
  • 7 juillet 2011, 10h-12h, salle B311 (LIPN)
  • 11 juillet 2011, 14h-16h, salle B311 (LIPN)
  • 13 juillet 2011, 14h-16h, salle B311 (LIPN)
LOVE 27/02/2019 Programmation dans les diagrammes de cordes et logique tensorielle, par Paul-André Melliès
Paul-André Melliès  
B311
27/02/2019    15:22 -
Résumé :

Dans la période du 4 au 13 juillet 2011, Paul-André Melliès (PPS, CNRS-Paris 7) propose un cycle de séminaires sur

Programmation dans les diagrammes de cordes et logique tensorielle

Le cycle est composé de quatre séances, ouvertes à tous, qui se tiendront à l'Institut Galilée et au LIPN, avec le calendrier suivant :
  • 4 juillet 2011, 14h-16h, amphi Euler (Institut Galilée)
  • 7 juillet 2011, 10h-12h, salle B311 (LIPN)
  • 11 juillet 2011, 14h-16h, salle B311 (LIPN)
  • 13 juillet 2011, 14h-16h, salle B311 (LIPN)
LOVE 27/02/2019 Programmation dans les diagrammes de cordes et logique tensorielle, par Paul-André Melliès
Paul-André Melliès  
B311
27/02/2019    15:22 -
Résumé :

Dans la période du 4 au 13 juillet 2011, Paul-André Melliès (PPS, CNRS-Paris 7) propose un cycle de séminaires sur

Programmation dans les diagrammes de cordes et logique tensorielle

Le cycle est composé de quatre séances, ouvertes à tous, qui se tiendront à l'Institut Galilée et au LIPN, avec le calendrier suivant :
  • 4 juillet 2011, 14h-16h, amphi Euler (Institut Galilée)
  • 7 juillet 2011, 10h-12h, salle B311 (LIPN)
  • 11 juillet 2011, 14h-16h, salle B311 (LIPN)
  • 13 juillet 2011, 14h-16h, salle B311 (LIPN)
LOVE 27/02/2019 On quantum complexity classes and quantum icc, par Margherita Zorzi
Margherita Zorzi  
B311
27/02/2019    15:22 -
Résumé :

Le 24 octobre 2011, à 14h en salle B311, le séminaire LCR accueille Margherita Zorzi (LIPN, post-doc ANR Complice).

One of the strong motivations behind quantum computing is computational complexity: quantum computers seem to be able to solve efficiently classical hard problems, thanks to the potential speed up in the execution time induced by superposition phenomena.

Quantum complexity theory has been developed since the Nineties, after the definition of quantum computational models such as quantum Turing machines and quantum circuit families. A particular attention is devoted to the quantum polytime classes (EQP, BQP, ZQP).

After a preliminarily discussion about quantum models and quantum complexity theory, the polytime quantum lambda calculus SQ (inspired by soft linear logic) is presented, showing an Implicit Computational Complexity approach in the quantum setting.
LOVE 27/02/2019 Graphes d'interaction, par Thomas Seiller
Thomas Seiller  
B311
27/02/2019    15:22 -
Résumé :

Le 16 janvier 2012, à 14h en salle B311, le séminaire LCR accueille Thomas Seiller (Chambéry).

Les graphes d'interaction généralisent la toute première géométrie de l'interaction définie par Girard dans l'article "Multiplicatives". En remplaçant les permutations (utilisées dans "Multiplicatives") par des graphes orientés pondérés, il est possible de définir une notion d'orthogonalité en comptant les cycles apparaissant lors du branchement de deux graphes. Il est alors possible d'obtenir une géométrie de l'interaction pour MALL dépendant de la fonction qui mesure les cycles.

Après avoir défini cette géométrie de l'interaction, je montrerai comment il est possible d'obtenir un modèle dénotationnel de MALL et une notion de vérité à partir de cette construction. Enfin, je montrerai qu'en choisissant judicieusement la fonction de mesure, il est possible d'obtenir soit la géométrie de l'interaction dans sa version ancienne (GdI1, avec une orthogonalité basée sur la nilpotence), soit une version combinatoire de la GdI5 de Girard. Ceci permet donc de donner une interprétation géométrique à l'orthogonalité de Girard basée sur le déterminant, et de relier cette nouvelle construction à celles plus anciennes basées sur la nilpotence.
LOVE 27/02/2019 Les stratégies pleinement paresseuses, par Thibaut Balabonski
Thibaut Balabonski  
B311
27/02/2019    15:22 -
Résumé :

Le 5 mars 2012, à 14h en salle B311, le séminaire LCR accueille Thibaut Balabonski (PPS).

Les stratégies de réduction avec partage fournissent des pistes pour l'évaluation efficace des programmes fonctionnels. En quarante ans, ces modes de réduction ont été définis dans des cadres formels variés, hétérogènes et parfois complexes, utilisant par exemple des clôtures, des graphes, ou des transformations de programmes.

Je présenterai un système de récriture simple et expressif dans lequel nombre de ces approches peuvent être unifiées, analysées, et comparées. On étudiera en particulier quelques avatars de la réduction pleinement paresseuse (dont une des variantes est implémentée dans le compilateur GHC) et on précisera en quoi ces différents systèmes sont équivalents. Enfin, une utilisation judicieuse d'une transformation de programmes classique (le lambda-lifting) permettra d'établir un lien entre la pleine paresse et la réduction optimale des systèmes du premier ordre.. Ce lien sera suffisamment fort pour permettre le transfert de propriétés non triviales du premier ordre vers le lambda-calcul.
LOVE 27/02/2019 A3: linear! dependent, par Arnaud Spiwack
Arnaud Spiwack  
B311
27/02/2019    15:22 -
Résumé :

Le 19 mars 2012, à 14h en salle B311, le séminaire LCR accueille Arnaud Spiwack (PiR2).

Herbelin & Curien's μ language gives a syntax to classical sequent calculus while leaving contraction and weakening implicit (more precisely dealt with by variables), like one would expect of a programming language. I will present an extension of H&C's μ for linear sequent calculus which still relies on variables for contraction and weakening. I will then proceed and show how to give it a hint of dependent types, though I must confess there are some troubles there.
LOVE 27/02/2019 Constructing differential categories and deconstructing categories of games, par Guy McCusker
Guy McCusker  
B311
27/02/2019    15:22 -
Résumé :

Le 12 mars 2012, à 14h en salle B311, le séminaire LCR accueille Guy McCusker (Université de Bath, invité LCR).

We present an abstract categorical construction of differential categories, that is categories suitable for modelling Ehrhard and Regnier's differential lambda calculus. We demonstrate that the relational model arises as an instance of our construction, as does a previously known category of games, exposing its differential nature that was not previously known. A new category of games is constructed in a similar way, and shown to be a fully complete model of a resource-sensitive version of PCF. The construction also gives us a collapse from the games model onto the relational model, which demonstrates that the relational model is fully abstract for resource PCF.

[Joint work with Jim Laird (Bath) and Giulio Manzonetto (LIPN, Paris 13)]
LOVE 27/02/2019 Introduction to triposes and intuitionistic realizability toposes, par Thomas Streicher
Thomas Streicher  
B311
27/02/2019    15:22 -
Résumé :

Le 19 mars 2012, à 13h30 en salle B311, le séminaire LCR accueille Thomas Streicher (Darmstadt).

A gentle introduction to the theory of triposes, intuitionistic realizability toposes, and the motivations behind them.
LOVE 27/02/2019 An imperative characterization of probabilistic polynomial time, par Paolo Parisen Toldin
Paolo Parisen Toldin  
B311
27/02/2019    15:22 -
Résumé :

Le 23 avril 2012, à 14h en salle B311, le séminaire LCR accueille Paolo Parisen Toldin (Bologne).

Contrary to ICC standard approach, we present a small WHILE language characterizing the class PP.

The main problem concerning the imperative approach is to understand how informations/values flow throw variables in a program.

In literature are well known many works that have polytime soundness but just few of them (using the imperative paradigm) are able to give a polytime completeness.

Our system, MAL0 (Multiplied, Affine, Linear, 0 dependeces ), is sound and complete. Moreover, our system can be used also to check if a program is running in probabilistic polytime (can be easily restrict to just polytime soundness). We claim that, contrary to works found in literature, our system is able to certify a program in polytime.

This is a joint work in progress with Jean-Yves Moyen.
LOVE 27/02/2019 Toward a bounded linear type system for pcf in call-By-value, par Barbara Petit
Barbara Petit  
B311
27/02/2019    15:22 -
Résumé :

Le 30 avril 2012, à 14h en salle B311, le séminaire LCR accueille Barbara Petit (Bologne).

 
LOVE 27/02/2019 Explicit substitutions at a distance, rewriting, and applications to the theory of lambda calculus, par Beniamino Accattoli
Beniamino Accattoli  
B311
27/02/2019    15:22 -
Résumé :

Le 14 mai 2012, à 14h en salle B311, le séminaire LCR accueille Beniamino Accattoli (LIX).

In some works in collaboration with Stefano Guerrini and Delia Kesner I developed a new approach to explicit substitutions, arising from Linear Logic proof-nets. The idea is to design calculi mimicking closely the dynamics of the graphical cut-elimination rules. Proof-nets and terms have very different notions of locality: this fact induce non-local, "at a distance" rewriting rules on terms. Substitution calculi at a distance are half-way lambda calculus and typical explicit substitution calculi: they retain most of the simplicity of lambda calculus, keeping the subtleties and the finer evaluation of explicit substitutions. In a series of recent works (some of which are joint works with Delia Kesner, Luca Paolini or Ugo Dal Lago) I explored systematically the rewriting theory of these calculi. In the talk I will survey the problems I studied (confluence, preservation of strong normalization, sigma-equivalence, developments, solvability, factorization, standardization, residuals) and the results I obtained, showing how they provide new understandings of classical notions and results - and sometimes even new results - in the theory of lambda-calculus.
LOVE 27/02/2019 The failure of the range property in the lambda theory h, par Andrew Polonsky
Andrew Polonsky  
B311
27/02/2019    15:22 -
Résumé :

Le 11 juin 2012, à 14h en salle B311, le séminaire LCR accueille Andrew Polonsky (Bergen).

We show that the lambda theory resulting from identification of all "meaningless" terms in the lambda calculus fails to satisfy the otherwise ubiquitous Range Property.  This is the condition that every term, seen via application as a map on closed terms, is either constant or has infinite range modulo identifications of the theory.  Specifically, we construct a term Xi such that in H one has for closed N:
Xi N = Xi I  <==>  Xi N =/= Xi Omega
The construction exposes certain pathological features of this
otherwise natural lambda theory.
LOVE 27/02/2019 Linearity in the non-Deterministic call-by-value setting, par Alejandro Di­az-Caro
Alejandro Di­az-Caro  
B311
27/02/2019    15:22 -
Résumé :

Le 7 juillet 2012, à 14h en salle B311, le séminaire LCR accueille Alejandro Di­az-Caro (LIPN).

We consider the non-deterministic extension of the call-by-value lambda calculus, which corresponds to the additive fragment of the linear-algebraic lambda-calculus. We define a fine-grained type system, capturing the right linearity present in such formalisms. After proving the subject reduction and the strong normalisation properties, we propose a translation of this calculus into the System F with pairs, which corresponds to a non linear fragment of linear logic. The translation provides a deeper understanding of the linearity in our setting, which we will discuss in this presentation.

Joint work with Barbara Petit. To appear in LNCS ( Proceedings of WoLLIC'12 ). arXiv:1011.3542
LOVE 27/02/2019 Caractérisation de co-NL par l'action d'un groupe, par Clément Aubert
Clément Aubert, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 13:30
Résumé :
Girard, dans Normativity in Logic (2011), propose un emploi innovant de la Géométrie de l'Interaction (GdI) dans le facteur hyperfini pour caractériser des classes de complexité. Ce papier étant très technique et parfois allusif, nous proposons avec Thomas Seiller (LAMA - Université de Savoie) une relecture des résultats qu'il présente. En allégeant et simplifiant certaines définitions et critères, en introduisant un modèle de calcul innovant (les machines à pointeurs non-déterministes), nous parvenons à prouver de nouveau que co-NL peut être caractérisé par l'action du groupe des permutations finies sur une algèbre de von Neumann.
Un bagage minimum de Logique Linéaire et de complexité sont souhaitables pour comprendre les grandes lignes, nous n'entrerons pas dans le détail des preuves techniques concernant la GdI ou les algèbres de von Neumann, préférant renvoyer le lecteur intéressé (et patient !) vers notre papier (en anglais), disponible à http://lipn.fr/~aubert/article-coNL.pdf
LOVE 27/02/2019 Opérades et Surjections, par Muriel Livernet
Muriel Livernet, LAGA, Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
Dans un premier temps j'expliquerai sur des exemples simples ce que sont les opérades. Dans un deuxième temps j'introduirai l'opérade des surjections et exposerai les questions combinatoires que l'on se pose afin de résoudre des problèmes en topologie algébrique.
LOVE 27/02/2019 Interaction Graphs and Complexity, par Thomas Seiller
Thomas Seiller, IHES  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
We obtained, with C. Aubert, new characterizations of complexity classes coNL and L using methods inspired from Girard's hyperfinite Geometry of Interaction (GoI). These characterizations had some drawbacks, among which:
- it used complicated tools from operator theory;
- it was not related to the interpretation of logic in the Geometry of Interaction construction;

This work revisits these previous results by using Interaction Graphs, a combinatorial GoI construction developed during my thesis that simplifies, unifies and generalizes Girard's GoI constructions. This change of perspective allows for a number of improvements, namely:
- the obtention of simplified characterizations of the classes coNL and L;
- the obtention of new characterizations, e.g. Regular languages, NL;
- it relates the method to the reconstruction of logic in Interaction Graphs (hence in GoI);
- it offers new ways to obtain characterizations of other classe.
LOVE 27/02/2019 On the computational meaning of axioms, par Mattia Petrolo
Mattia Petrolo, IHPST, Paris 1  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
An anti-realist theory of meaning suitable for both logical and proper axioms is investigated. As opposed to other anti-realist accounts, like Dummett-Prawitz verificationism, the standard framework of classical logic is not called into question. The reason being that semantical features are not limited solely to inferential ones, but also computational aspects are considered as essential in the process of determination of meaning. In order to deal with such computational aspects, a relaxation of syntax is shown to be necessary. This leads to the presentation of a general kind of proof theory, where the objects of study are not only typed objects like deductions, but untyped ones, where formulas have been replaced by geometrical configurations.

This is joint work with Alberto Naibo and Thomas Seiller
LOVE 27/02/2019 De la charactérisation des modèles de H*, par Flavien Breuvart
Flavien Breuvart, PPS/LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 11:30
Résumé :
Je donnerais une caractérisation (pour une large classe de model du lambda calcul pur) des modèles qui sont pleinement adéquat pour la normalisation de tête, càd dont la théorie est H*. Un K-model extentionel D est pleinement adéquat sii il est hyperimmune, càd que les comportements mal fondés ne sont pas capturées par aucun terme récursif.
LOVE 27/02/2019 Lambda-calculus and the Invariance Thesis, par Beniamino Accattoli
Beniamino Accattoli, Università di Bologna  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :

Slot and van Emde Boas’s invariance thesis states that reasonable machines can simulate each other within a polynomially overhead in time. Is λ-calculus a reasonable ma- chine? Is there a way to measure the computational complexity of a λ-term? This paper presents the first complete positive answer to this long-standing problem. Moreover, our answer is completely machine-independent and based over a standard notion in the theory of λ-calculus: the invariant cost model is the length of a leftmost-outermost derivation to normal form. Such a theorem cannot be proved by directly relating λ-calculus with Turing machines or register machines, because of the size explosion problem: there are terms that in a linear number of steps produce an exponential output. The first step towards the solution is to shift to a notion of evaluation for which length and size of the output are linearly related. This is done by adopting the linear substitution calculus (LSC), a calculus of explicit substitutions modelled after linear logic proof nets and that admits a decomposition of leftmost-outermost derivations with the desired property. Thus, the LSC is invariant with respect to, say, register machines. The second step is to show that LSC is invariant with respect to the λ-calculus. The size explosion problem seems to imply that this is not possible: having the same notions of normal form, evaluation in the LSC is exponentially longer than in the λ-calculus. We solve such an impasse by introducing a new form of shared normal form and shared reduction, deemed useful. Useful evaluation avoids those unsharing steps that only explicit the output without contributing to β-redexes, i.e. the steps that cause the blow-up in size. The main technical contribution of the paper is indeed the definition of useful reduction and the thorough analysis of their properties.

LOVE 27/02/2019 Paramétricité et type identité : application à la structure d'É-groupoide des types, par Marc Lasson
Marc Lasson, PPS - PiR2  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé : 
La paramétricité est un concept introduit par Reynolds afin d'étudier
l'abstraction de type polymorphe du système F. Elle renvoie au
fait que des programmes bien typés ne peuvent ``inspecter le type de leurs
arguments'': ils doivent se comporter uniformément au regard des
types abstraits. Reynolds formalise cette notion en montrant que les
programmes polymorphes du système F satisfont des relations
logiques définies par induction sur la structure des types. Le système de
types sous-jacent à coq est suffisamment expressif pour exprimer
sa propre théorie de la paramétricité. Dans cet exposé, nous nous
intéresserons aux conséquences de cette remarque lorsqu'elle est
appliquée au type des égalités, et nous montrerons en particulier comment
montrer des résultats de paramétricité concernant les espaces de lacet
(loop spaces, en anglais) et en déduire des résultats sur la structure de
groupoide de la théorie des types.
LOVE 27/02/2019 Two Intensional Phenomena: The Size of Church-Rosser Diagrams, and Characterization of PTIME via Overlapping Cons-Free Systems, par Jakob Grue Simonsen
Jakob Grue Simonsen, Datalogisk Institut, Copenhague  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
We will informally discuss two very different problems that both concern the intensional behaviour of very simple calculi: First-order term rewriting systems, respectively lambda calculus.

The first problem concerns finding bounds on the size of confluence and Church-Rosser diagrams: If s is a term in a confluent, we know that every "peak" t *<-s ->* t' has a corresponding "valley" t ->* s' *<- t', but it is not at all clear how the number of steps in the "valley" relates
to the number of steps in the "peak" and to the size of the starting term s. We will discuss how valley sizes can always be computed, how
the sizes may majorize any computable function on the integers, how exponential bounds can be found for first-order term rewriting, and
for lambda calculus how there is an enormous difference between the best-known upper bound (not even elementary recursive) and the worst-case example known (doubly exponential).

The second problem concerns implicit complexity and how to characterize the set of PTIME-decidable sets by first-order term rewriting systems
in the most liberal fashion possible: No restrictions on reduction strategy (hence no insistence on call-by-name, call-by-value or other
functional-programming-inspired strategies), no restrictions on overlaps between left-hand sides of rules, and as few linearity constraints as we can get away with (and absolutely no explicit typing of any kind).

The talk will be kept at high-level and present the interesting problems and challenges; we will only delve into technical details if the audience feels like it. The material presented is based on joint, ongoing, work with Jeroen Ketema and Daniel de Carvalho.
LOVE 27/02/2019 Ludique et types: éléments de déconstruction, par Christophe Fouqueré
Christophe Fouqueré, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
We will discuss/analyze the following observations and the questions they rise:

Observations:
- Each formula of MALL2 is denoted by a behaviour in Ludics.
- Cut-elimination is fully plugged into / at the heart of Ludics.
- And with properties expected for a logic.

Questions:
- Can we characterize exactly behaviours that denote MALL(c/2/inf) formulas?
- Can we define the algebraic structure of a behaviour? I.e. a language for behaviours?
- Can we develop a sequent calculus for this language?
LOVE 27/02/2019 Behavior driven design for tests and verification, par Ulrich Kühne
Ulrich Kühne, University of Bremen  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé : 
In the course of an exploratory project on hardware and system design and verification, we are looking for new ways how to bridge the gap between early abstract models and later implementation phases. One possible approach is the adaptation of agile techniques to the hardware domain, enhanced by model checking techniques. While in the design of hardware systems, testing and verification are usually applied as a post-process, software developement is pushed towards agile techniques like Test Driven Development (TDD), where tests play a central role.  Behavior driven development (BDD) extends TDD as a well established software development technique. Essentially, in both techniques testing and implementing is interleaved, with the test cases being written first. In BDD, test cases are written in natural language which enables the discussion with stakeholders and easy requirements tracking throughout the design. In this talk, I will present a BDD tool for the Verilog hardware design language, which extends BDD with formal techniques. From test cases, properties can be generalized, making the verification more reliable, without the need to manually specify temporal properties.
LOVE 27/02/2019 Can Dialectica break bricks?, par Pierre-Marie Pédrot
Pierre-Marie Pédrot, PPS, Université Paris 7  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :

The Dialectica translation is a logical transformation described by Gödel in 1958, but designed in the 30's. At the end of the 80's, it was given a categorical counterpart, which happened to be compatible with the usual decomposition of intuitionistic logic into linear logic. Still, it was lacking a true Curry-Howard interpretation.

We will fill this hole by presenting the computational content of Dialectica by means of an untyped lambda-calculus translation. We will show that this translation has a really simple explanation as soon as we put our source term in the Krivine abstract machine, except for a disturbing detail, seemingly deeply rooted in linear logic. We will also show how our presentation can be naturally applied to a dependently-typed system almost without adaptation, thus giving a hindsight on how linear dependent types may be built (or not).
LOVE 27/02/2019 Data-race freedom by typing in Mezzo, par Thibaut Balabonski
Thibaut Balabonski, INRIA  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 11:30
Résumé : 
Mezzo is a typed programming language in the ML family whose static discipline controls aliasing and ownership. This rules out certain mistakes, including representation exposure and data races, and opens up new opportunities, such as gradual initialization or (more generally, and somewhat speculatively) the definition and enforcement of object protocols.

In this talk, I will explain the basic design of Mezzo on examples, and show how its type system inspired by separation logic gives a simple way of tracking ownership of fragments of shared memory between concurrent threads. Beyond the usual claim that "well-typed programs do not go wrong", we guarantee that well-typed Mezzo programs have no data-races.
LOVE 27/02/2019 Quelques remarques d'ordre logique sur la théorie des types homotopiques (1ère partie), par Christophe Fouqueré
Christophe Fouqueré, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
A partir du livre "Homotopy Type Theory", seront abordés les points suivants: théorie des types (à la Martin-Löf), notions (très) élémentaires d'homotopie et axiome d'univalence, hiérarchisation des types et conséquences sur la partie interprétant la logique (en particulier le tiers-exclus). Nous n'aborderons pas nombre de points (théorie des catégories, types homotopiques d'ordre supérieur, reconstruction des réels, ...) hautement intéressants de ce livre.
LOVE 27/02/2019 Présentation de l2coq : une bibliothèque pour des preuves linéaires en Coq, par Micaela Mayero
Micaela Mayero, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
Dans cette séance je présenterai l2coq, développé par O. Laurent et D. Pous. Il s'agit d'un "sous-ensemble de Coq" (sous la forme d'une bibliothèque "restrictive") permettant de faire des preuves de propriétés linéaires (ILL, ELL, LLL, SLL). Olivier en avait fait une présentation le jour de la soutenance d'HDR de Virgile. En 1 an, l2coq a continué d'évoluer. Je vous propose de revenir sur les bases de l2coq en vous montrant également le code et j'expliquerai pourquoi j'ai mis quelques mots entre guillemet dans les phrases précédentes. Pour cela, je ferai des rappels (ou pas pour certains) de la théorie de Coq en me basant sur l'exposé précédent de Christophe, la partie théorie des types. Vers la fin ou en cours d'exposé, je vous ferai une démo, durant laquelle nous pourrons tenter ensemble de faire des preuves formelles de propriétés linéaires (ILL dans un premier temps).
LOVE 27/02/2019 Quelques remarques d'ordre logique sur la théorie des types homotopiques (2e partie), par Christophe Fouqueré
Christophe Fouqueré, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 13:30
Résumé :
A partir du livre "Homotopy Type Theory", seront abordés les points suivants: théorie des types (à la Martin-Löf), notions (très) élémentaires d'homotopie et axiome d'univalence, hiérarchisation des types et conséquences sur la partie interprétant la logique (en particulier le tiers-exclus). Nous n'aborderons pas nombre de points (théorie des catégories, types homotopiques d'ordre supérieur, reconstruction des réels, ...) hautement intéressants de ce livre.
LOVE 27/02/2019 Models of a Non-Associative Composition, par Guillaume Munch-Maccagnoni
Guillaume Munch-Maccagnoni, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
We characterise the polarised evaluation order through a categorical structure where the hypothesis that composition is associative is relaxed. Duploid is the name of the structure, as a reference to Jean-Louis Loday's duplicial algebras. The main result is a reflection Adj→Dupl where Dupl is a category of duploids and duploid functors, and Adj is the category of adjunctions and pseudo maps of adjunctions. The result suggests that the various biases in denotational semantics: indirect, call-by-value, call-by-name... are a way of hiding the fact that composition is not always associative.
LOVE 27/02/2019 Proving complexity bounds in linear logic with context semantics, par Matthieu Perrinel
Matthieu Perrinel, ENS Lyon  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé : 
First, I will present a simplified version of Ugo Dal Lago's context
semantics on proof-nets. Next, I will present abstract properties based on
context semantics which entail complexity bounds. I will use this
properties to make short proofs of strong complexity bounds for ELL and
LLL. Finally, I will sketch how we are currently using context semantics to
give new type systems characterizing Ptime and the first LL-based type
system characterizing primitive recursive functions.
LOVE 27/02/2019 Intensionnalité vs. extensionnalité : où est-elle la frontière ? (3e partie), par Jean-Yves Moyen
Jean-Yves Moyen, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
Au cours de ces trois séances de groupe de travail, je ferai le "débriefing" de mon CRCT et je vous présenterai les résultats obtenus à Nancy en collaboration avec Guillaume Bonfante et Pierre, ou à Copenhague en collaboration avec James Avery et Jakob Simonsen (qui sera par ailleurs prof invité chez nous en février).

Au gré de vos interruptions et de nos discussions, nous parlerons sans doute de Rice et de Gödel, de cardinaux et de grands ordinaux, d'ordre supérieur et de non déterminisme, de treillis, de partitions, peut-être de topologie. Les catégoriciens pourront s'exercer à faire commuter des diagrammes. Ne reniant pas mes origines, tout cela sera enrobé dans une couche de complexité implicite.


Le point de départ est une relecture du théorème de Rice entamée avec Pierre il y a quelques années. Au lieu de parler de "propriétés extensionnelles", le résultat est vu comme parlant de l'équivalence extensionnelle (p et q sont équivalents si ils calculent la même fonction). Autrement dit, on quotiente l'ensemble des programmes par leur extension.

Cette vision fait de Rice une équivalence parmi d'autres et on peut chercher d'autres équivalences "intéressantes" entre programmes. Notamment, l'ensemble des équivalences formant un treillis complet, on peut étudier ce treillis.
LOVE 27/02/2019 Intensionnalité vs. extensionnalité : où est-elle la frontière ? (2e partie), par Jean-Yves Moyen
Jean-Yves Moyen, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
Au cours de ces trois séances de groupe de travail, je ferai le "débriefing" de mon CRCT et je vous présenterai les résultats obtenus à Nancy en collaboration avec Guillaume Bonfante et Pierre, ou à Copenhague en collaboration avec James Avery et Jakob Simonsen (qui sera par ailleurs prof invité chez nous en février).

Au gré de vos interruptions et de nos discussions, nous parlerons sans doute de Rice et de Gödel, de cardinaux et de grands ordinaux, d'ordre supérieur et de non déterminisme, de treillis, de partitions, peut-être de topologie. Les catégoriciens pourront s'exercer à faire commuter des diagrammes. Ne reniant pas mes origines, tout cela sera enrobé dans une couche de complexité implicite.


Le point de départ est une relecture du théorème de Rice entamée avec Pierre il y a quelques années. Au lieu de parler de "propriétés extensionnelles", le résultat est vu comme parlant de l'équivalence extensionnelle (p et q sont équivalents si ils calculent la même fonction). Autrement dit, on quotiente l'ensemble des programmes par leur extension.

Cette vision fait de Rice une équivalence parmi d'autres et on peut chercher d'autres équivalences "intéressantes" entre programmes. Notamment, l'ensemble des équivalences formant un treillis complet, on peut étudier ce treillis.
LOVE 27/02/2019 Intensionnalité vs. extensionnalité : où est-elle la frontière ? (1ère partie), par Jean-Yves Moyen
Jean-Yves Moyen, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
Au cours de ces trois séances de groupe de travail, je ferai le "débriefing" de mon CRCT et je vous présenterai les résultats obtenus à Nancy en collaboration avec Guillaume Bonfante et Pierre, ou à Copenhague en collaboration avec James Avery et Jakob Simonsen (qui sera par ailleurs prof invité chez nous en février).

Au gré de vos interruptions et de nos discussions, nous parlerons sans doute de Rice et de Gödel, de cardinaux et de grands ordinaux, d'ordre supérieur et de non déterminisme, de treillis, de partitions, peut-être de topologie. Les catégoriciens pourront s'exercer à faire commuter des diagrammes. Ne reniant pas mes origines, tout cela sera enrobé dans une couche de complexité implicite.


Le point de départ est une relecture du théorème de Rice entamée avec Pierre il y a quelques années. Au lieu de parler de "propriétés extensionnelles", le résultat est vu comme parlant de l'équivalence extensionnelle (p et q sont équivalents si ils calculent la même fonction). Autrement dit, on quotiente l'ensemble des programmes par leur extension.

Cette vision fait de Rice une équivalence parmi d'autres et on peut chercher d'autres équivalences "intéressantes" entre programmes. Notamment, l'ensemble des équivalences formant un treillis complet, on peut étudier ce treillis.
LOVE 27/02/2019 Bisimulations from graphical encodings (DPOs, RPOs, cospans, and all that), par Fabio Gadducci
Fabio Gadducci, Università di Pisa  
Amphi Copernic, Institut Galilée, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé : 
The talk presents a personal recollection of recent results on the synthesis of labelled transition systems (LTSs) for process calculi. 
The starting point is a visual technique for modelling the reduction semantics of nominal calculi: processes are mapped into graphs equipped with "interfaces", such that the denotation is fully abstract with respect to the structural congruence. The encoding allows for the reuse of standard graph rewriting theory and tools for simulating the reduction semantics of the calculus, such as the "double pushout" (DPO) approach and its concurrent semantics (which allows for the simultaneous execution of independent reductions)
Graphs with interfaces are just an instance of a cospan category (over the category of graphs). which is amenable to the synthesis mechanism based on "borrowed contexts" (BCs), proposed by Ehrig and Koenig, which are in turn an instance of "relative push outs" (RPOs), originally introduced by Milner and Leifer. The BC mechanism allows for the effective construction of an LTS that has graphs with interfaces as both states and labels, and such that the associated bisimilarity is automatically a congruence. 
Since the category of cospans over graphs admits RPOs (as proved by Sassone and Sobocinski), its choice as the domain of the encoding for nominal calculi ensures that the synthesis of an LTS can be performed, and that a compositional observational equivalence is obtained. The talk discusses the LTS distilled by exploiting the encoding of CCS and Mobile Ambients processes.
LOVE 27/02/2019 From Mind to Turing to Mind, par Henk Barendregt
Henk Barendregt, Radboud University Nijmegen  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 13:30
Résumé :
Based on introspection Alan Turing analyzed the process by which humans perform  computations. Recent papers on consciousness go in the other direction: this is seen as a hybrid Turing machine process. Hybrid in the sense that it acts both discretely and in parallel, where the Turing machine quadruplets are implemented by a neural net.

We also focus on mind-states and their possible implementations in the brain, based on recent progress in neuroscience.

If the claims in the talk are validated one day, then this would be emperical evidence for the Church-Turing thesis
LOVE 27/02/2019 Graphical Foundations for Dialogue Games, par Cai Wingfield
Cai Wingfield, University of Bath  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 14:00
Résumé : 
In 2007, Harmer, Hyland and Melliès gave a formal mathematical foundation for game semantics using a notion they called a schedule, a structure describing interleavings of plays in games.  Their definition was combinatorial in nature, but researchers often draw pictures when describing schedules in practice.  Moreover, several proofs of key properties, such as that the composition of schedules is associative, involve cumbersome combinatorial detail, whereas in terms of pictures the proofs are straightforward, reflecting the geometry of the plane.  Here, we give a geometric formulation of schedules, prove that they are isomorphic to Harmer et al.'s definitions, and illustrate their value by giving such geometric proofs.  Harmer et al.'s notions may be combined to describe plays in multi-component games, and researchers have similarly developed intuitive graphical representations of plays in these games.  We give a characterisation of these diagrams and explicitly describe how they relate to the underlying schedules, finally using this relation to provide new, intuitive proofs of key categorical properties.

This is a joint work with Guy McCusker and John Power.
LOVE 27/02/2019 Forcing in classical realizability: the case study of Herbrand trees, par Lionel Rieg
Lionel Rieg, ENS Lyon  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 14:30
Résumé :
Krivine presented in 2010 a methodology to combine Cohen's forcing with the theory of classical realizability and showed that the forcing condition can be seen as a reference that is not subject to backtracks. The underlying classical program transformation was then analyzed by Miquel (2011) in a fully typed setting in classical higher-order arithmetic (PAw+).

As a case study of this methodology, I present a method to extract a Herbrand tree from a classical realizer of an existential formula, following the idea of the proof of Herbrand theorem.  Unlike the traditional proof based on Konig's lemma (using a fixed enumeration of atomic formulas), our method is based on the introduction of a particular Cohen real.  It is formalized as a proof in PAw+, making explicit the construction of generic sets in this framework in the particular case where the set of forcing conditions is arithmetical.  We then analyze the algorithmic content of this proof.
LOVE 27/02/2019 Some Results for Linear Logic Full Completeness, par Hugh Steele
Hugh Steele, IML, Aix-Marseille  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 14:00
Résumé : 
Many full completeness theorems have been established for fragments of
linear logic since the notion was first defined by Samson Abramsky and
Radha Jagadeesan in their 1992 paper. For the most part, these results
are obtained on a case-by-case basis: the subject of each proof is
precisely one category.

In this talk it is shown that the Hyland-Tan double glueing
construction can transform all tensor-generated compact closed
categories with finite biproducts into fully complete models of
unit-free MLL. The arguments employed are based around considering the
combinatorics behind the construction using standard linear algebra.
It is also discussed how another double glueing construction may be
able to create similar categories satisfying unit-free MALL full
completeness.
LOVE 27/02/2019 Hypercoherence Spaces form a double-glued Category , par Hugh Steele
Hugh Steele, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
Ehrhard's Hypercoherence Spaces proved a useful medium through which to study strongly stable semantics. The category of hypercoherence spaces (HypCoh) has also been shown to be the bedrock of one of the very few fully complete models of unit-free multiplicative additive linear logic, satisfying Joyal's softness condition. Much like in the category of coherence spaces (Coh), an object of HypCoh is a set equipped with a collection of its subsets, with morphisms being relations respecting restrictions set by these `cliques'. However, unlike Coh, HypCoh has not been formalised as a true double-glued category.

In this talk I show that HypCoh is indeed such a category (if you're willing to bend the rules a little!). We also see how far the spirit of the glueing construction may be generalised to produce categories with similar properties.
LOVE 27/02/2019 Are partial orderings intrinsic to computations?, par Antonino Salibra
Antonino Salibra, Università Ca' Foscari Venezia  
Salle à fixer, Université de Villetaneuse
27/02/2019    15:22 - 13:30
Résumé : 
Answering a question by Honsell and Plotkin, we show that there are two equations between lambda terms, the so-called subtractive equations, consistent with lambda calculus but not contemporaneously satisfied in any Scott continuous model. We also relate the subtractive equations to the open problem of the order-incompleteness of lambda calculus, by studying the connection between the notion of absolute unorderability in a specific point and a weaker notion of subtractivity, namely n-subtractivity, for partially ordered algebras. Finally we study the relation between n-subtractivity and relativized separation conditions in topological algebras, obtaining an incompleteness theorem for a general topological semantics of lambda calculus.
LOVE 27/02/2019 Some Results for Linear Logic Full Completeness, par Hugh Steele
Hugh Steele, IML, Aix-Marseille  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 13:30
Résumé : 
Many full completeness theorems have been established for fragments of
linear logic since the notion was first defined by Samson Abramsky and
Radha Jagadeesan in their 1992 paper. For the most part, these results
are obtained on a case-by-case basis: the subject of each proof is
precisely one category.

In this talk it is shown that the Hyland-Tan double glueing
construction can transform all tensor-generated compact closed
categories with finite biproducts into fully complete models of
unit-free MLL. The arguments employed are based around considering the
combinatorics behind the construction using standard linear algebra.
It is also discussed how another double glueing construction may be
able to create similar categories satisfying unit-free MALL full
completeness.
LOVE 27/02/2019 On type isomorphisms in simultaneous presence of sums and functions, par Danko Ilik
Danko Ilik, LIX, Ecole polytechnique  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé : 
We consider the problem of characterizing isomorphisms of types, or, equivalently, constructive cardinality of sets, in the simultaneous presence of disjoint unions, Cartesian products, and exponentials. Mostly relying on results about polynomials with exponentiation that have not been used in our context, we derive: that the usual finite axiomatization known as High-School Identities (HSI) is complete for a significant subclass of types; that it is decidable for that subclass when two types are isomorphic; that, for the whole of the set of types, a recursive extension of the axioms of HSI exists that is complete; and that, for the whole of the set of types, the question as to whether two types are isomorphic is decidable when base types are to be interpreted as finite sets. We also point out certain related open problems.
LOVE 27/02/2019 A Core Quantitative Coeffect Calculus, par Aloïs Brunel
Aloïs Brunel, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:15
Résumé :
Monadic notions of computation are well-established mechanisms used to express effects in pure functional languages. Less well-established is the notion of comonadic computation. However, recent works have shown the usefulness of comonads to structure context dependent computations. In this talk, we present a language, called lRPCF, inspired by a generalized interpretation of the exponential modality of bounded linear logic. In lRPCF exponential modalities carry a label--an element of a semiring--providing additional information on how a program uses its context. This additional information is used to express comonadic type analysis.
LOVE 27/02/2019 Game semantics and applications to compilation (1/3): Semantic foundations of heterogeneous compilation, par Dan Ghica
Dan Ghica, University of Birmingham  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 15:30
Résumé : 
This is an introductory, motivational and methodological talk in which I will describe my "Seamless Computing" research programme. By "seamless" I mean that programming languages for unconventional architectures (e.g. distributed, reconfigurable, heterogeneous) can still conform to the long-established principles of machine independence, recast in this new setting. I will talk about when and how such conventional languages (higher-order, imperative, concurrent) can be compiled in a seamless way, using ideas based on the Geometry of Interaction and on game semantics.
LOVE 27/02/2019 Game semantics and applications to compilation (2/3): Abstract machines for game semantics, par Dan Ghica
Dan Ghica, University of Birmingham  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 15:30
Résumé : 
We will examine new abstract machines for game semantics which correspond to networks of conventional computers, and which can be used as an intermediate representation for distributed compilation. This is achieved in two steps. First we introduce the HRAM, a Heap and Register Abstract Machine, an abstraction of a conventional computer, which can be structured into HRAM nets, an abstract point-to-point network model. HRAMs are multi-threaded and subsume communication by tokens (cf. IAM) or jumps (cf. JAM). Game Abstract Machines (GAM), are HRAMs with additional structure at the interface level, but no special operational capabilities. We show that GAMs cannot be naively composed, but composition must be mediated using special HRAM combinators. HRAMs are flexible enough to allow the representation of game models for languages with state (non-innocent games) or concurrency (non-alternating games). We illustrate the potential of this technique by implementing a toy distributed compiler for ICA, a higher-order programming language with shared state concurrency, thus significantly extending our previous distributed PCF compiler. We show that compilation is sound and memory-safe, i.e. no (distributed or local) garbage collection is necessary. [Joint work with Olle Fredriksson, to appear at LICS'13]
LOVE 27/02/2019 Vers une meilleur compréhension de l'adéquation complète, par Flavien Breuvart
Flavien Breuvart, Paris 7 (PPS)  
Salle A303, LIPN
27/02/2019    15:22 - 14:30
Résumé : 
L'adéquation complète est une propriété liant un modèle dénotationnel et
une syntaxe qui assure une identité entre l’équivalence observationnel et
l'équivalence dénotationnel. Deux programmes sont dits
observationnellement équivalents s'ils se comportent à l’identique quelque
soit le contexte (cf bisimulations) et sont dits dénotationnellement
équivalent s'ils ont la même interprétation dans le modèle.
Nous allons alors regarder de plus près cette propriété pour se rendre
compte qu'elle implique généralement des preuves non triviales. Puis nous
étudierons les différentes techniques de preuves de la littérature. Et
enfin, partant d'une technique de preuve original, nous essayerons
d'établir une caractérisation de l'adéquation complète dans le cas
particulier du lambda-calcul et des modèles de Krivines (ou des modèles de
filtres ou encore des typages avec intersection).
LOVE 27/02/2019 Linear Dependent Types For Differential Privacy, par Marco Gaboardi
Marco Gaboardi, University of Pennsylvania / Università di Bologna  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 14:30
Résumé : 
Differential privacy offers a way to answer queries about
sensitive information while offering strong, provable privacy guarantees.
 Several tools have been developed for certifying that a given query is
differentially private. In one approach, Reed and Pierce[31] proposed a
functional programming language, Fuzz, for writing differentially private
queries. Fuzz uses linear types to track sensitivity, as well as a
probability monad to express randomized computation; it guarantees that any
program that has a certain type is differentially private. Fuzz can
successfully verify many useful queries. However, it fails when the
analysis depends on values that are not known statically.
We present DFuzz, an extension of Fuzz with a combination of linear indexed
types and lightweight dependent types. This combination allows a richer
sensitivity analysis that is able to analyze a larger class of queries,
including queries whose sensitivity depends on runtime information. As in
Fuzz, the differential privacy guarantees follows directly from the
soundness theorem for the type system. We demonstrate the enhanced
expressivity of DFuzz by certifying differential privacy a broad class of
iterative algorithms that could not be typed previously. We conclude by
discussing the challenges of DFuzz type checking.
LOVE 27/02/2019 Unification and Logarithmic space , par Marc Bagnol
Marc Bagnol, IML, Université Aix-Marseille  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
I will present an algebraic characterization of the complexity
classes Logspace and NLogspace, using an algebra with a composition
law based on unification. This bridge between unification and
complexity classes is inspired from proof theory and more specifically
linear logic and Geometry of Interaction.
LOVE 27/02/2019 Unfolding-based Reachability Checking of Petri Nets, par César Rodríguez
César Rodríguez, LCR  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 17:00
Résumé :
In model checking, a well known source of state-space explosion (SSE) is the explicit representation of concurrent actions by their interleavings. Partial-order reductions attempt to address this by constructing an equivalent state space where irrelevant executions of the original are discarded. A comparatively less well-known approach emerges from the use of partial-order semantics, where the state space is instead represented by a partial order where concurrent actions are simply left unordered. Petri net unfoldings are arguably the most prominent verification technique issued from this idea. In this talk, three different semantics for Petri nets will be presented, the last one of which will be the aforementioned unfolding semantics. We will then see how unfoldings can be employed in practical verification and, time permitting, how to improve the method to address additional sources of SSE.
LOVE 27/02/2019 Asynchronous Interaction with Theorem Provers: ProofGeneral's Last March, par Carst Tankink
Carst Tankink, Inria Saclay  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
This year ProofGeneral, the generic Emacs-interface for proof assistants, celebrates its 20th birthday. The tool is showing its age, however, by only allowing a user to work at a single point at the time, and having to re-evaluate an entire proof script in reaction to changes at the beginning. In this talk, I will discuss our recent efforts to changing this situation: based on a previous endeavour in Isabelle, we have adapted the Coq proof assistant to work with the jEdit text editor. This editor has no user-visible notion of "State": the entire proof is always available to the proof assistant, allowing it to react to changes in the document in a more intelligent manner: by scheduling proofs in parallel and by postponing computation that are of no direct interest to the author. I will not go into full technical details in this talk, but give a demo of the current prototype, and discuss the ramifications of such a model in the longer term.
LOVE 27/02/2019 Construction de l'exponentielle libre en logique linéaire, par Luc Pellissier
Luc Pellissier, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
Groupe de travail sur une extension des méthodes introduites par Paul-André Melliès et Nicolas Tabareau pour calculer le comonoïde commutatif libre dans une catégorie avec produits (c.-à-d. un modèle de la logique linéaire multiplicative additive). On introduira les concepts nécessaires (PROPs, extensions de Kan, fins, etc.) et on expliquera sous quelles conditions on peut donner une formule close pour le calcul du comonoïde commutatif libre. On verra que ces conditions sont vérifiées dans tous les modèles connus de la logique linéaire, alors que les conditions originalement proposées par Melliès et Tabareau ne sont pas vérifiées par le modèle des espaces de finitude.
LOVE 27/02/2019 The implementation of GPGPU for Model Checking Problems, par WU Zhimin
WU Zhimin, Nanyang Technological University, Singapore  
Salle A303
27/02/2019    15:22 - 16:30
Résumé :
In this presentation, I will introduce the implementation of GPGPU techniques in model checking area. I target Nvidia GPU so firstly, the latest CUDA Compute Architecture will be introduced, together with the key points of GPU Program optimization. Then I will refer to some existing research on GPU accelerated Model Checking Problems. Finally, I will briefly introduce my research work. (This will be an informal presentation.)
LOVE 27/02/2019 Modèles et paradigmes de programmation parallèle distribuée, par Camille Coti
Camille Coti, AOC, LIPN, Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 16:30
Résumé :
Dans cette présentation, qui sera plus un panorama qu'un séminaire de recherche, je présenterai quelques grands paradigmes de programmation parallèle distribuée à travers les modèles de mémoire distribuée et de communications inter-processus. Le but de mon exposé sera de présenter comment le caractère distribué des données est représenté et manipulé dans ces paradigmes de programmation afin de réfléchir à quelles techniques de programmation adopter selon les patterns d'accès aux données d'un programme séquentiel que l'on souhaite paralléliser. Je mettrai l'accent sur la mémoire distribuée, la mémoire partagée distribuée, les sacs de tâches, les communications implicites unilatérales et bilatérales, la parallélisation automatique par compilation.
LOVE 27/02/2019 Introduction to Partial Order Reductions , par César Rodríguez
César Rodríguez, LCR, LIPN, Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 17:00
Résumé :
In model checking, a well known source of state-space explosion (SSE) is the explicit representation of concurrent actions by their interleavings. Partial-order reductions (PORs) are a family of techniques attempting to cope with this by constructing an equivalent state space where irrelevant executions of the original are discarded. This talk will be a gentle introduction to the topic. We will focus on Godefroid's persistent sets, prove that a selective exploration based on them visits all deadlocks, discuss the two main classes of algorithms for computing them, and finish, time permitting, with an overview of the conceptual similarities and differences between PORs and the unfolding technique.
LOVE 27/02/2019 Approche philologique des langages de programmation, par Baptiste Mélès
Baptiste Mélès, Archives Poincaré  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
La théorie des langages de programmation s'appuie généralement sur des langages de programmation théoriques — lambda-calcul, machines de Turing, et leurs variantes — que l'on suppose représenter fidèlement — à compilation près ! — les propriétés des langages de programmation de la « vraie vie », si l'on entend par là ceux que les programmeurs utilisent pour écrire des programmes utiles au quotidien : C, C++, Perl, etc. Or nous allons voir que les langages de programmation de la vraie vie possèdent bien des propriétés dont nul ne voudrait dans un langage théorique, et que la compilation écrase : des commandes inutiles, des redondances, des résidus purement historiques... Qui plus est, loin d'être un fait simplement négatif, ces propriétés constituent une bonne part de leur expressivité du point de vue du programmeur, et sont autant de points communs avec les langues naturelles. Nous verrons ainsi que des outils linguistiques et philologiques peuvent être mobilisés pour décrire une « sémantique du programmeur », qui échappe pour une bonne part aussi bien aux sémantiques courantes des langages de programmation qu'aux tentatives de description formelle de l'expressivité des langages de programmation.
LOVE 27/02/2019 New applications of moment-SOS hierarchies, par Victor Magron
Victor Magron, Imperial College London  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
Semidefinite programming is relevant to a wide range of mathematic fields, including combinatorial optimization, control theory, matrix completion. In 2001, Lasserre introduced a hierarchy of semidefinite relaxations for particular polynomial instances of the Generalized Moment Problem (GMP). My talk emphasizes new applications of this moment-SOS hierarchy, investigated during my PhD and Postdoc research. In the context of formal proofs for nonlinear optimization, one can combine the moment-SOS hierarchy with maxplus approximation of semiconvex functions. Such a framework is mandatory for formal certification of nonlinear inequalities, occurring by thousands in the proof of Kepler Conjecture by Hales. I also present how to approximate, as closely as desired, the Pareto curve associated with bicriteria polynomial optimization problems or the projections of semialgebraic sets. For each problem, one builds a hierarchy of semidefinite programs, so that the sequence of bounds converges in L1 norm. Finally, this hierarchy allows to analyze programs containing loop invariants with polynomial assignments.
LOVE 27/02/2019 Chemins en ludique non-linéaire, par Alice Pavaux
Alice Pavaux, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
La ludique est une théorie logique basée sur l'interaction, introduite il y a une quinzaine d'années par J.-Y. Girard. Elle s'inscrit dans un contexte marqué par les avancées importantes en théorie de la démonstration et en sémantique des langages de programmation permises par la logique linéaire. On se propose ici d'étudier les mécanismes de l'interaction dans une variante non-linéaire de la ludique, afin de poser les outils nécessaires à l'étude des types dans ce cadre. Cela se fera en décrivant les chemins suivis au cours de l'interaction au sein des desseins, les objets de la ludique. La non-linéarité permet de ne pas se restreindre au fragment multiplicatif-additif de la logique linéaire.
LOVE 27/02/2019 Abstraction and Modular Verification of Services Using Symbolic Observation Graph (SOG), par Hanene Ochi
Hanene Ochi, LCR, LIPN, Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 16:30
Résumé :
For automatically composing services in a correct manner, information about their behaviors (an abstract model) has to be published in a repository. This abstract model must be sufficient to decide whether two, or more, services are compatible (the composition is possible) without including any additional information that can be used to disclose the privacy of these services. The compatibility between two services can be based either on some generic properties or specific ones . This talk will present my work during my thesis about the problem considering these kinds of compatibility criteria, and we will introduce approches for the automatic abstraction of services and to the modular checking of their compatibility using their abstract models only. To abstract services, we use the symbolic observation graph (SOG) approach that preserves necessary informa tion for service composition and hides private information. We will show how the SOG can be adapted and used so that the verification of generic and specific compatibility criteria can be performed on the composition of the abstract models of services instead of the original composite service.
LOVE 27/02/2019 Precise Robustness Analysis of Real-Time Systems, par Étienne André
Étienne André, LCR, LIPN, Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 17:00
Résumé :
Quantifying the robustness of a real-time system consists in measuring the maximum extension of the timing delays such that the system still satisfies its specification. In this work, we introduce a more precise notion of robustness, measuring the allowed variability of the timing delays in their neighbourhood. We consider here the formalism of time Petri nets extended with inhibitor arcs. We use the inverse method, initially defined for timed automata. Its output, in the form of a parametric linear constraint relating all timing delays, allows the designer to characterise the system local robustness, and hence to identify the delays allowing the least variability. We also exhibit a condition and a construction for rendering robust a non-robust system. This work is a joint work with Laure Petrucci.
LOVE 27/02/2019 CosyVerif: An Open Source Extensible Verification Environment, par Étienne André
Étienne André, LCR, LIPN, Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 17:00
Résumé :
Over the past two decades, numerous verification tools have been successfully used for verifying complex concurrent systems, modelled using various formalisms. However, it is still hard to coordinate these tools since they rely on such a large number of formalisms. Having a proper syntactical mechanism to interrelate them through variability would increase the capability of eff ective integrated formal methods. Here, we propose a modular approach for defining new formalisms by reusing existing ones and adding new features and/or constraints. Our approach relies on standard XML technologies; their use provides the capability of rapidly and automatically obtaining tools for representing and validating models. It thus enables fast iterations in developing and testing complex formalisms. As a case study, we applied our modular definition approach on families of Petri nets and timed automata. This work is implemented in the CosyVerif platform, a modular framework integrating verification software tools of the Paris regions. This is a joint work with the CosyVerif team.
LOVE 27/02/2019 Teaching Formal Methods: Experience at UPMC and UP13 with CosyVerif, par Laure Petrucci
Laure Petrucci, LCR, LIPN, Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 17:00
Résumé :
Nowadays, students are more and more demanding for practical coursework, which is a challenge when teaching formal approaches to software engineering. The solution is to provide environments for such hands-on sessions and homework, but this raises numerous difficulties. The environment must be: (i) multi-platform (Mac OS, Linux, Windows) so as to enable student practice at home, (ii) easy to deploy, (iii) easy to use and to take charge of, and (iv) flexible enough to enable the integration of new notations and associated services. CosyVerif is a software environment dedicated to graphical notations, that provides the mechanisms and means for an easy integration of additional existing software for teaching (or demonstration) purposes. This makes it an interesting platform to establish new courses. This paper presents our experience using CosyVerif for teaching Petri nets and parametric timed automata in two universities of the Paris region, i.e. Université Pierre et Marie Curie, and Université Paris 13. We also use CosyVerif to build demonstrators of Ph.D. students' work.
LOVE 27/02/2019 Cost Linear Temporal Logic for Verification, par Maximilien Colange
Maximilien Colange, CUI Université de Genève  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 16:30
Résumé :
Qualitative formal verification aims at checking that a given formal property holds on a model, given as an automaton. The automata-based approach expresses the property as an automaton then analyses its synchronisation with the model automaton. This method can be extended with various automata flavors to handle quantitative properties. We focus on an extension of Linear Temporal Logic (LTL) with counting capabilities: Cost Linear Temporal Logic (CLTL). This logics can be translated into Büchi automata equipped with counters, so as to nicely extend the automata approach to model-checking. We describe the new properties that this extension allows to handle, illustrated with examples. We also explain how it is linked to existing qualitative LTL model-checking, and the new challenges it poses. We also propose a CEGAR-like approach to answer compute the bounds of the values reached by the automata.
LOVE 27/02/2019 Cost Linear Temporal Logic for Verification, par Maximilien Colange
Maximilien Colange, CUI Université de Genève  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 14:40
Résumé :
Qualitative formal verification aims at checking that a given formal property holds on a model, given as an automaton. The automata-based approach expresses the property as an automaton then analyses its synchronisation with the model automaton. This method can be extended with various automata flavors to handle quantitative properties. We focus on an extension of Linear Temporal Logic (LTL) with counting capabilities: Cost Linear Temporal Logic (CLTL). This logics can be translated into Büchi automata equipped with counters, so as to nicely extend the automata approach to model-checking. We describe the new properties that this extension allows to handle, illustrated with examples. We also explain how it is linked to existing qualitative LTL model-checking, and the new challenges it poses. We also propose a CEGAR-like approach to answer compute the bounds of the values reached by the automata.
LOVE 27/02/2019 Vérification de Spécifications EB-3 à l'aide de Techniques de Model Checking, par Dimitrio Vekris
Dimitrio Vekris, LACL, Université Paris-Est Créteil  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 15:20
Résumé :
EB-3 est un langage de spécification développé pour la spécification des systèmes d'information. Le noyau du langage EB-3 comprend des spécifications d'algèbre de processus afin de décrire le comportement des entités du système et des fonctions d'attributs qui sont des fonctions récursives dont l'évaluation se fait sur la trace d'exécution du système décrivant les attributs des entités. La vérification de propriétés temporelles en EB-3 est un sujet de grande importance pour des utilisateurs de EB-3. Dans cet exposé, on se focalise sur les propriétés de vivacité concernant des systèmes d'information exprimant l'éventualité que certaines actions puissent s'exécuter. La vérification des propriétés de vivacité se fait à l'aide de model checking. En se basant sur une sémantique opérationnelle de EB-3, selon laquelle les fonctions d'attributs sont évaluées pendant l'exécution du programme puis stockées, on définit une traduction automatique de EB-3 vers LNT, qui est un langage simultané enrichi d'une algèbre de processus. Notre traduction assure la correspondance un à un entre les états et les transitions des systèmes étiquetés de transition correspondent respectivement à des spécifications EB-3 et LNT. Ensuite, on automatise la traduction grâce à l'outil EB3toLNT fournissant aux utilisateurs de EB-3 tous les outils de vérification fonctionnelle disponible dans CADP.
LOVE 27/02/2019 Specification and verification of Time Petri Nets with Coq, par Amal Chamakh
Amal Chamakh, LCR, LIPN, Université Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 17:00
Résumé :
Model checking and theorem proving, have long reached their limitation as general-purpose techniques, and most of the research now is concentrated on efficient specialization of both approaches to relatively narrow problem domains. The state space explosion problem leaves little hope for automatic finite-state verification techniques like model checking to remain practical, especially when designs become parameterized. The use of theorem proving techniques is inevitable to cope with the new verification challenges. "Pure" theorem proving, on the other hand, can also be quite tedious and impractical for complex designs. Ideally, one would like to find an efficient combination of model checking and theorem proving, and the quest for such a combination has long been one of the major challenges in the field of formal verification. In this paper, we address the combination of model checking and theorem proving approaches in order to specify and to model check Time Petri Nets (TPN) model-based systems. In particular, we show how a TPN is specified using the Coq proof assistant, and how the fireability/unfireability of a timed sequence of transitions can be proved. This allows, for instance, to prove the reachability of a given state by the firing of a given timed/untimed trace or to prove that a counter-example supplied by a given (untimed) model checker is a real counterexample of a timed system. %First, we provide a formalization of the net model in COQ via the parsing of its Petri Net Markup Language (PNML) description. Then the COQ proof assistant is used to prove the firability (or the opposite) of traces given by model checking as a counter-example when a propriety being checked is found to be non-valid, hence, states reachability is proved.
LOVE 27/02/2019 Une introduction à la théorie de Squier, par Yves Guiraud
Yves Guiraud, Inria PiR2  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
Un monoïde ayant une présentation par un système de réécriture convergent fini a un problème du mot décidable. Dans les années 1980, Jantzen s'interroge sur la réciproque : un monoïde ayant un problème du mot décidable admet-il toujours une présentation par un système de réécriture convergent fini ? Squier a répondu négativement à cette question en reliant des propriétés algorithmiques des systèmes de réécriture, comme la terminaison et la confluence, à des invariants algébriques, comme l'homologie ou l'homotopie. Dans cet exposé, je présenterai le résultat initial de Squier, dans le formalisme de la réécriture de dimension supérieure. Puis, nous verrons comment le travail de Squier permet aujourd'hui d'utiliser la réécriture comme méthode constructive pour calculer des invariants de structures algébriques.
LOVE 27/02/2019 Model checking en logique de dépendance, par Nicolas de Rugy-Altherre
Nicolas de Rugy-Altherre, Équipe de logique, Paris 7  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:45
Résumé :
La logique de dépendance et ses variantes (indépendance et inclusion) ont été introduites par Vänäänen il y a quelques années pour parler de façon "propre" de dépendance en logique. Je présenterai cette logique et ses résultats principaux en complexité.
LOVE 27/02/2019 Coherence spaces for computable analysis, par Kazushige Terui
Kazushige Terui, RIMS Kyoto University  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
Abstract: There have been two mainstream approaches in computable analysis: the type-two theory of effectivity (TTE) and the theory of domain representations. This paper proposes an intermediary approach based on coherence spaces, which is as concrete as TTE and as structured as domain theory. We import various concepts from TTE such as admissibility, and provide admissible representations for the real line, Euclidean spaces and function spaces over them. This allows us to represent, for instance, a real continuous function by a stable map. A natural question is then what linear maps correspond to in terms of analysis. Our answer is that they correspond to uniformly continuous functions. This leads to an internal expression of Heine's theorem (every continuous function on a compact interval of the real line is uniformly continuous) as the existence of a certain map from a stable function space to a linear function space. We finally illustrate an application of coherence spaces as a type system for lambda calculus, which allows us to verify local properties of real functions. This is a joint work with Kei Matsumoto.
LOVE 27/02/2019 Modelling Timed Concurrent Systems Using Activity Diagram Patterns, par Étienne André
Étienne André, LCR, LIPN, Université Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 17:00
Résumé :
UML is the de facto standard for modelling concurrent systems in the industry. Activity diagrams allow designers to model workflows or business processes. Unfortunately, their informal semantics prevents the use of automated verification techniques. In this paper, we first propose activity diagram patterns for modelling timed concurrent systems; we then devise a modular mechanism to compose timed diagram fragments into a UML activity diagram that also allows for refinement, and we formalise the semantics of our patterns using time Petri nets. Our approach guides the modeller task% (helping to avoid common mistakes), and allows for automated verification. Joint work with Christine Choppy and Thierry Noulamo
LOVE 27/02/2019 The Plotkin's call-by-value lambda-calculus from a linear-logical viewpoint, par Giulio Guerrieri
Giulio Guerrieri, PPS, Université Paris Diderot  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
We translate the terms of ordinary lambda-calculus into proof-nets accordingly the Girard's call-by-value "boring'' encoding of intuitionistic implication A->B = !A-o!B. We show that (1) the Plotkin's call-by-value beta-reduction is (bi)simulated in proof-nets via cut-elimination; (2) there is a sequentialization theorem that characterizes all and only the proof-nets which are translations of some lambda-term; (3) the equivalence relation on lambda-terms which identifies lambda-terms having the same translation in proof-nets is the call-by-value counterpart of Regnier's sigma-equivalence and is not included in Plotkin's call-by-value beta-equivalence. The semantics of lambda-terms is preserved by our call-by-value sigma-equivalence. Adding an oriented version of the call-by-value sigma-rules to the call-by-value beta-reduction (and keeping the same syntax of ordinary lambda-calculus) we preserve confluence and we get a call-by-value operational characterization of solvable and potential valuable terms (this is not possible in original Plotkin's call-by-value lambda-calculus). Moreover, we give a semantic characterization of solvable and potential valuable terms in a relational model, based on Linear Logic, satisfying the Taylor expansion formula. As a technical tool, we also use a resource-sensitive calculus in which the elements of the model are definable.
LOVE 27/02/2019 Functors are Type Refinement Systems, par Noam Zeilberger
Noam Zeilberger, MSR-INRIA Joint Centre, Mathematical Components group  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
The standard reading of type theory through the lens of category theory is based on the idea of viewing a type system as a category of well-typed terms. In this joint work with Paul-André Melliès we propose a basic revision of this reading: rather than interpreting type systems as categories, we describe them as functors from a category of typing derivations to a category of underlying terms. Then, turning this around, we explain how in fact *any* functor gives rise to a generalized type system, with an abstract notion of typing judgment, typing derivations and typing rules. This leads to a purely categorical reformulation of various natural classes of type systems as natural classes of functors. In the talk I want to motivate and introduce this general framework (which can also be seen as providing a categorical analysis of _refinement types_), and as a larger example give a sketch of how the framework can be used to formalize an elegant proof of a coherence theorem by John Reynolds. If time permits, I will also describe some of the natural questions raised by this perspective that are the subject of ongoing research.
LOVE 27/02/2019 An infinitary model of linear logic, par Charles Grellois
Charles Grellois, PPS & LIAFA, Université Paris Diderot  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
We construct an infinitary variant of the relational model of linear logic, where the exponential modality is interpreted as the set of finite or countable multisets. We explain how to interpret in this model the fixpoint operator Y as a Conway operator alternatively defined in an inductive or a coinductive way. We then extend the relational semantics with a notion of color or priority in the sense of parity games. This extension enables us to define a new fixpoint operator Y combining both inductive and coinductive policies. We conclude by sketching the connection between the resulting model of lambda-calculus with recursion and higher-order model-checking.
LOVE 27/02/2019 Linear numeral systems, par Ian Mackie
Ian Mackie, LIX - École polytechnique  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
We take a fresh look at an old problem of representing natural numbers in the lambda-calculus. Our interest is in finding representations where we can compute efficiently (and where possible, in constant time) the following functions: successor, predecessor, addition, subtraction and test for zero. Surprisingly, we find a solution in the linear lambda-calculus, where copying and erasing are not permitted.
LOVE 27/02/2019 On an Extension of Freeze LTL with Ordered Attributes, par Normann Decker
Normann Decker, Institute for Software Engineering and Programming Languages, University of Lübeck  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 10:30
Résumé :
We present an extension of Freeze LTL, a temporal logic equipped with registers, over data words. Each position in a (multi-attributed) data word carries a letter from a finite alphabet and assigns a data value to a fixed, finite set of attributes. While reasoning on collections of data values is valuable for expressing correctness properties of executions of dynamic programs the satisfiability problem of Freeze LTL is undecidable if more than one register is available or tuples of data values can be stored and compared arbitrarily. Our extension therefore allows for specifying a dependency relation on attributes. These dependencies introduce a restricted, yet flexible way of storing and comparing collections of attribute values. This new dimension of flexibility is orthogonal to, e.g., the number of registers or the available temporal operators. In this setting we characterise precisely the type of dependency relations that maintain decidability of the logic. To this end, we employ reductions from and to nested counter systems. Moreover, by a complexity theoretic characterisations we can show that our extension is strict and induces a semantic hierarchy of logical fragments.
LOVE 27/02/2019 Building Bridges Between Sets of Partial Orders, par Hernán Ponce de León
Hernán Ponce de León, Department of Information and Computer Science, Aalto University (Finland)  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 17:00
Résumé :
Partial orders are a fundamental mathematical structure capable of representing concurrency and causality on a set of atomic events. In many applications it is essential to consider multiple partial orders, each representing a particular behavioral scenario or an operating mode of a modeled system. In this talk I will present two mathematical formalisms capable of the compressed representation of sets of partial orders: Labeled Event Structures (LESs) and Conditional Partial Order Graphs (CPOGs). I will demonstrate their advantages and disadvantages and propose efficient algorithms for transforming of a set of partial orders from a given compressed representation in one formalism into an equivalent representation in another formalism without the explicit enumeration of each scenario. These algorithms make use of an intermediate mathematical formalism, which we call Conditional Labeled Event Structures (CLESs), that combines the advantages of LESs and CPOGs. This is joint work with Andrey Mokhov (Newcastle University)
LOVE 27/02/2019 Effective verification of low-level software with nested interrupts, par Lihao Liang
Lihao Liang, Université d'Oxford  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 15:30
Résumé :
Interrupt-driven software is difficult to test and debug, especially when interrupts can be nested and subject to priorities. Interrupts can arrive at arbitrary times, leading to an explosion in the number of cases to be considered. We present a new formal approach to verifying interrupt-driven software based on symbolic execution. The approach leverages recent advances in the encoding of the execution traces of interacting, concurrent threads. We assess the performance of our method on benchmarks drawn from embedded systems code and device drivers, and experimentally compare it to conventional formal approaches that use source-to-source transformations. Our experimental results show that our method significantly outperforms conventional techniques. To the best of our knowledge, our technique is the first to demonstrate effective formal verification of low-level embedded software with nested interrupts. Joint work with Daniel Kroening, Tom Melham, Peter Schrammel and Michael Tautschnig
LOVE 27/02/2019 Enhanced Distributed Behavioral Cartography of Parametric Timed Automata, par Hoang Gia Nguyen
Hoang Gia Nguyen, LCR, LIPN, Université Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 15:30
Résumé :
Parametric timed automata (PTA) allow the specification and verification of timed systems incompletely specified, or subject to future changes. The behavioral cartography splits the parameter space of PTA in tiles in which the discrete behavior is uniform. Applications include the optimization of timing constants, and the measure of the system robustness w.r.t. the untimed language. Here, we present enhanced distributed master-worker algorithms to compute the cartography efficiently. Experimental results show that our new algorithms significantly outperform previous distribution techniques.
LOVE 27/02/2019 "Formalising Concurrent UML State Machines Using Coloured Petri Nets", par Mohamed Mahdi Benmoussa
Mohamed Mahdi Benmoussa, LCR, LIPN, Université Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 15:30
Résumé :
While UML state machines are widely used to specify dynamic systems behaviours, their semantics is described informally, which prevents the complex systems verification. In this paper, we propose a formalisation of concurrent UML state machines using coloured Petri nets. We consider in particular concurrent aspects (orthogonal regions, forks, joins, shared variables), the hierarchy induced by composite states and their associated activities, internal/external/local transitions, and entry/exit/do behaviours.
LOVE 27/02/2019 gdt Homotopy Type Theory - séance 1, par Andrew Polonsky
Andrew Polonsky, équipe LCR, LIPN, Université Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
The first of a little series of talks on Homotopy Type Theory (i.e., higher-order algebraic treatment of the notion of equality in dependant type theory). Logical relations are a technique for proving meta-theoretic properties of type systems. In recent years, they have received a lot of attention as it became clear that logical relations give the most natural definition of extensional equality in type theory. A major open problem is to define a type system which contains extensional equality as an internal type constructor. For this, it is necessary to reflect the external logical relation back into the syntax of the type language. In this talk I will describe how to do this.
LOVE 27/02/2019 Reachability Preservation Based Parameter Synthesis for Timed Automata, par Étienne André
Étienne André, LCR, LIPN, Université Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 15:30
Résumé :
The synthesis of timing parameters consists in deriving conditions on the timing constants of a concurrent system such that it meets its specification. Parametric timed automata are a powerful formalism for parameter synthesis, although most problems are undecidable. We first address here the following reachability preservation problem: given a reference parameter valuation and a (bad) control state, do there exist other parameter valuations that reach this control state iff the reference parameter valuation does? We show that this problem is undecidable, and introduce a procedure that outputs a possibly underapproximated answer. We then show that our procedure can efficiently replace the behavioral cartography to partition a bounded parameter subspace into good and bad subparts; furthermore, our procedure can even outperform the classical bad-state driven parameter synthesis semi-algorithm, especially when distributed on a cluster.
LOVE 27/02/2019 Configuration Structures, par Clément Aubert
Clément Aubert, INRIA, LACL, Université Paris Est-Créteil  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
A standard contextual equivalence for process algebras is strong barbed congruence. Configuration structures are a denotational semantics for processes in which one can define equivalences that are more discriminating, i.e. that distinguish the denotation of terms equated by barbed congruence. Hereditary history preserving bisimulation (hhpb) is such a relation. We define a strong back and forth barbed congruence using a reversible process algebra and show that the relation induced by the back and forth congruence is equivalent to hhpb. Hence we give a characterization of hhpb as a contextual equivalence in a reversible process algebra. Joint work with Ioana Cristescu.
LOVE 27/02/2019 On the dependencies of logical rules, par Alexis Saurin
Alexis Saurin, PPS, Université Paris Diderot  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
Many correctness criteria have been proposed since linear logic was introduced and it is not clear how they relate to each other. We present proof-nets and their correctness criteria from the perspective of dependency, as introduced by Mogbil and Jacobé de Naurois. More precisely, we introduce a new correctness criterion, called DepGraph, and show that together with Danos' contractibility criterion and Mogbil and Naurois criterion, they form the three faces of a notion of dependency which is crucial for correctness of proof-structures. Finally, we extract the logical meaning of the dependency relation and show that it allows to recover and characterize some constraints on the ordering of inferences which are implicit in the proof-net. Joint work with Marc Bagnol and Amina Doumane.
LOVE 27/02/2019 Action synthesis for branching time logic: theory and applications, par Micha? Knapik
Micha? Knapik, Instytut Podstaw Informatyki, Polskiej Akademii Nauk  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 15:30
Résumé :
Action-Restricted Computation Tree Logic (ARCTL) is a simple extension of CTL, proposed by Pecheur and Raimondi, where the actions allowed along the considered runs can be explicitly indicated by path selectors. ARCTL allows to express properties such as "a safe state is unavoidable for every path built from Forward and Left actions", denoted by AF{Forward,Safe}safe. By replacing the concrete sets of actions with free variables we obtain a parametric version of the logic pmARCTL, where properties such as AF{X}safe are allowed, where X is a parameter. We introduce a fixed-point theory that allows for the exhaustive synthesis of all the valuations of the variables which make the pmARTCL formulae hold in a given model. The theory has been implemented in an open source stand-alone tool and evaluated on scalable examples with promising results.
LOVE 27/02/2019 Model-checking for efficient malware detection, par Tayssir Touili
Tayssir Touili, LCR, LIPN, Université Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 15:30
Résumé :
The number of malware is growing extraordinarily fast. Therefore, it is important to have efficient malware detectors. Malware writers try to obfuscate their code by different techniques. Many of these well-known obfuscation techniques rely on operations on the stack such as inserting dead code by adding useless push and pop instructions, or hiding calls to the operating system, etc. Thus, it is important for malware detectors to be able to deal with the program's stack. In this talk I will show a new model-checking approach for malware detection that takes into account the behavior of the stack. Our approach consists in : (1) Modeling the program using a Pushdown System (PDS). (2) Introducing new logics, called SCTPL and SLTPL, to represent the malicious behavior. SCTPL (resp. SLTPL) can be seen as an extension of the branching-time temporal logic CTL (resp. the linear-time temporal logic LTL) with variables, quantifiers, and predicates over the stack. (3) Reducing the malware detection problem to the model-checking problem of PDSs against SCTPL/SLTPL formulas. We show how our new logics can be used to precisely express malicious behaviors that could not be specified by existing specification formalisms. We then consider the model-checking problem of PDSs against SCTPL/SLTPL specifications. We provide efficient algorithms to solve these problems. We implemented our techniques in a tool, and we applied it to detect several viruses. Our results are encouraging. In particular, our tool was able to detect more than 800 viruses. Several of these viruses could not be detected by well-known anti-viruses such as Avira, Avast, Norton, Kaspersky and McAfee.
LOVE 27/02/2019 BE-PUM: A tool of Binary Emulation for Pushdown Model generation, par Quan Thanh Tho
Quan Thanh Tho, Ho Chi Minh City University of Technology, Vietnam  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 13:15
Résumé :
In this talk, we present the tool BE-PUM (Binary Emulation for PUshdown Model generation) for binary analysis. As suggested by its name, BE-PUM generates pushdown model, which is considered as a control flow graph (CFG) combined with a memory execution model. BE-PUM also introduces a concolic approach in order to generate CFG in a more precise manner. As such, BE-PUM is able to handle various popular obfuscation techniques of malwares, such as indirect jump or self- modification code. In experiments, we are able to produce models for around 1700 samples of real malware. Compared to JakStab and IDA Pro, two state-of-the-art tools in this field, BE-PUM shows better tracing ability, sometimes with significant differences.
LOVE 27/02/2019 Interacting Hopf algebras: the theory of linear systems, par Fabio Zanasi
Fabio Zanasi, Radboud University of Nijmegen  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
We present by generators and equations the theory IH whose free model is the category of linear subspaces over a field k. Terms of IH are string diagrams which, for different choices of k, express different kinds of networks and graphical formalisms used by scientists in various fields, such as quantum circuits, electrical circuits and signal flow graphs. The equations of IH arise by distributive laws between PROPs of Hopf algebras – from which the name interacting Hopf algebras. The characterisation in terms of subspaces allows to think of IH as a string diagrammatic syntax for linear algebra: linear maps, spaces and their transformations are all faithfully represented in the graphical language, resulting in an alternative, often insightful perspective on the subject matter. As main application, we use IH to axiomatise a formal semantics of signal processing circuits, for which we study full abstraction and realisability. Our analysis suggests a reflection about the role of causality in the semantics of computing devices. This is a joint work with Filippo Bonchi and Pawel Sobocinski.
LOVE 27/02/2019 The Y=Y(SI) problem, par Andrew Polonsky
Andrew Polonsky, PPS, Paris 7  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
We discuss an important problem in untyped lambda calculus. Put forward by Statman, it asks whether there exists a fixed point combinator Y such that Y=Ydelta, where delta = SI = \yx.x(yx). It is conjectured that there is no such Y. After basic introduction and examples, we will show how Statman's conjecture naturally generalizes in two directions. In the first perspective, we investigate general conditions on terms G1,..,GN which are fpc generators: for all terms M, M fpc => M G1 .. GN fpc In the second direction, we look at the simply-typed \Y-calculus, in which a "formal" fpc is introduced together with the rewrite rule Yx –> x(Yx) Given an arbitrary fpc Y, there is an obvious interpretation of this calculus in the untyped lambda calculus. The Y=Y(SI) conjecture is reduced to the conservativity of this interpretation, for any Y.
LOVE 27/02/2019 Hacking Nondeterminism with Induction and Coinduction, par Damien Pous
Damien Pous, LIP, ENS Lyon  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
Finite automata are used in a wide range of verification problems. We introduce "bisimulation up to congruence" as a technique for proving language equivalence of non-deterministic finite automata. Exploiting this technique, we devise an optimisation of the classical algorithm by Hopcroft and Karp which, as we show, is exploiting a weaker "bisimulation up to equivalence" technique. The resulting algorithm can be exponentially faster than the recently introduced "antichain algorithms".
LOVE 27/02/2019 Timed Aggregate Graph : a finite graph for model checking of Time Petri Nets , par Amal Chamakh
Amal Chamakh, LCR, LIPN, Université Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 15:00
Résumé :
Time Petri Nets (TPNs) are one of the most powerful formalisms for the specification and the verification of systems involving explicit timing constraints. To deal with model checking of timed systems modeled by TPNs, we propose a new finite graph, called Timed Aggregate Graph (TAG), abstracting the behavior of bounded TPNs with strong time semantics. The main feature of this abstract representation compared to existing approaches is the encoding of the time information. This is done in a pure way within each node of the TAG allowing to compute the minimum and maximum elapsed time in every path of the graph. The TAG preserves timed traces and reachable states of the corresponding TPN and allows for on-the-fly verification of reachability properties. We also introduce an algorithm for a modular construction of the TAG, to better confine the state explosion problem.
LOVE 27/02/2019 Parameter Synthesis for Parametric Interval Markov Chains, par Laure Petrucci
Laure Petrucci, LCR, LIPN, Université Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 15:00
Résumé :
Interval Markov Chains (IMCs) are the base of a classic probabilistic specification theory introduced by Larsen and Jonsson in 1991. They are also a popular abstraction for probabilistic systems. In this paper we study parameter synthesis for a parametric extension of Interval Markov Chains in which the endpoints of intervals may be replaced with parameters. In particular, we propose constructions for the synthesis of all parameter values ensuring several properties such as consistency and consistent reachability in both the existential and universal settings with respect to implementations. We also discuss how our constructions can be modified in order to synthesise all parameter values ensuring other typical properties. Joint work with Benoît Delahaye and Didier Lime
LOVE 27/02/2019 Relational type-checking of connected proof-structures, par Luc Pellissier
Luc Pellissier, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
It is possible to define a typing system for Multiplicative Exponential Linear Logic (MELL): in such a system, typing judgments are of the form ? R : x : ?, where R is a MELL proof-structure, ? is the list of types of the conclusions of R, and x an element of the relational interpretation of ?, meaning that x is an element of the relational interpretation of R (of type ?). As relational semantics can be used to infer execution properties of the proof-structure, these judgment can be considered as forms of quantitative typing. We provide an abstract machine that decides, if R satisfies a geometric condition, whether the judgment ? R : x : ? is valid. Also, the machine halts in bilinear time in the sizes of R and x.
LOVE 27/02/2019 Caractérisation impérative des algorithmes séquentiels en temps quelconque, primitif récursif et polynomial, par Yoann Marquer
Yoann Marquer, IRIF  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
Les fonctions calculables ont été formalisées par différents modèles de calcul (récursion, lambda-calcul, machines de Turing) ayant le même comportement entrées-sortie : c'est la thèse de Church. Par exemple, une machine de Turing à un ruban peut simuler les résultats calculés par une machine à deux rubans. Pourtant, pour la reconnaissance de palindrome la machine à un seul ruban nécessite une complexité en temps supérieure. Ainsi, il faut étudier les étapes intermédiaires. Nous définissons donc une simulation pas à pas entre exécutions, utilisant uniquement des variables temporaires et une dilatation temporelle. La thèse de Church concernait donc les fonctions, et il nous faut une nouvelle thèse pour les algorithmes. Nous avons choisi celle de Gurevich pour sa présentation axiomatique : un algorithme séquentiel est un objet vérifiant les trois postulats de temps séquentiel, d'états abstraits et d'exploration bornée. De plus, il a montré que les algorithmes séquentiels coïncident avec son modèle des Abstract State Machines. Nous dirons donc qu'un modèle de calcul est algorithmiquement complet s'il existe une simulation mutuelle d'exécutions entre lui et les ASMs. Pour obtenir des résultats sur des modèles de calcul plus usuels, nous formalisons les langages impératifs par un système de transition. En étudiant leur sémantique opérationnelle pas à pas et en développant une notion de graphe d'exécution, nous montrons qu'une variante du langage While de Jones est algorithmiquement complète. Ce résultat étant à structures de données près, il correspond donc à une équivalence entre les structures de contrôle des ASMs et des langages impératifs. De plus, étant préoccupés par la faisabilité des algorithmes, nous montrons que les structures du premier ordre utilisées par Gurevich permettent bien d'implémenter les structures de données usuelles. Notre soucis de la faisabilité nous a également conduit à étudier en terme de complexité implicite deux restrictions des ASMs : celles en temps primitif récursif (les opérations usuelles et terminales) et celles en temps polynomial (les exécutions réalistes). Nous montrons d'une part que si les structures de données sont également primitives récursives, alors une variante LoopC du langage Loop de Meyer et Ritchie est complète pour les algorithmes en temps primitif récursif. D'autre part, une restriction syntaxique LoopCstat de LoopC est complète pour les algorithmes en temps polynomial, sans restriction sur les structures de données et en caractérisant syntaxiquement le degré du polynôme.
LOVE 27/02/2019 Open Call-by-Value, par Giulio Guerrieri
Giulio Guerrieri, IRIF  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
The elegant theory of the call-by-value lambda-calculus relies on weak evaluation and closed terms, that are natural hypotheses in the study of programming languages. To model proof assistants, however, strong evaluation and open terms are required, and it is well known that the operational semantics of call-by-value becomes problematic in this case, as first pointed out by Paolini and Ronchi della Rocca. Here we study the intermediate setting—that we call Open Call-by-Value—of weak evaluation with open terms, on top of which Grégoire and Leroy designed the abstract machine of Coq. Various calculi for Open Call-by-Value already exist, coming from logical, semantical, or implementative points of view, each one with its pros and cons. This paper presents a detailed comparative study of their operational semantics. First, we show that all calculi are equivalent from a termination point of view, justifying the slogan Open Call-by-Value. Second, we compare their equational theories. Third, we present a detailed quantitative analysis of the time cost model. Four, we introduce a new simple abstract machine, and prove it a reasonable implementation of Open Call-by-Value with respect to its cost model. Along the way, there emerges a sharp deconstruction of call-by-value evaluation and of the complexity of its implementations. (Joint work with Beniamino Accattoli)
LOVE 27/02/2019 Interaction Graphs and Quantitative Semantics, par Thomas Seiller
Thomas Seiller, DIKU, Copenhague  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
Interaction Graphs (IG) models were introduced as a generalisation of GirardÂ’s Geometry of Interaction (GOI) constructions based on the interpretation of proofs as (finite, weigthed) graphs. Recent results use IG models to bring into vision a new relation between dynamic and denotational semantics. The first contribution of this work is the definition of categories of triskells, which generalises both the bicategory of spans and the categories of matrices and arrays over a semiring (also known as categories of weighted relations). Secondly, it sheds light onto a new relationship between dynamic and quantitative denotational semantics for multiplicative linear logic (MLL), providing formal grounds to the claim that IG models are a quantitative generalisation of dynamic semantics, i.e. GOI and game semantics. Finally, this functor is shown to preserve not only the interpretation of proofs but also induced double-glueing refinements: it is shown to lift to a map from the double-glueing construction defining IG models to the double-glueing construction yielding coherence spaces. For this purpose, a very general notion of quantitative coherence spaces is introduced, and shown to model full linear logic.
LOVE 27/02/2019 String diagrams for Proof nets, par Matteo Acclavio
Matteo Acclavio, I2M, Marseille  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
Sequentialization of MELL proof nets needs additional tools extern to interaction nets syntax: connectivity, switchings, boxes and jumps. In this talk we introduce string diagrams syntax for monoidal categories in order to present a model for proof nets (with the relative cut elimination) with a unique local sequentialization criterion for MLL with constants and an idea for a generalization of this result for MELL proof nets.
LOVE 27/02/2019 New Results on Morris's Observational Theory: the benefits of separating the inseparable, par Giulio Manzonetto
Giulio Manzonetto, LIPN, Université Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
We study the theory of contextual equivalence in the untyped lambda-calculus, generated by taking the normal forms as observables. Introduced by Morris in 1968, this is the original extensional lambda theory H+ of observational equivalence. On the syntactic side, we show that this lambda-theory validates the omega-rule, thus settling a long-standing open problem. On the semantic side, we provide sufficient and necessary conditions for relational graph models to be fully abstract for H+. We show that a relational graph model captures Morris's observational pre-order exactly when it is extensional and lambda-König. Intuitively, a model is lambda-König when every lambda-definable tree has an infinite path which is witnessed by some element of the model. Joint work with Flavien Breuvart, Domenico Ruoppolo & Andrew Polonsky
LOVE 27/02/2019 La hiérarchie du temps logarithmique, par Damiano Mazza
Damiano Mazza, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
Pendant le développement de travaux en cours avec Cynthia Kop et Jakob Simonsen j'ai eu l'occasion d'étudier un peu plus de près la classe de complexité LH, ou hiérarchie en temps logarithmique, qui est peut-être plus connue dans sa version non-uniforme sous le nom de AC^0 (circuits booléens avec fan-in arbitraire, de taille polynomiale et profondeur constante). Je vais vous parler un peu de cette hierarchie et plus en particulier de son niveau 0, appelé DLOGTIME, qui constitue probablement l'une des plus petites classes de complexité ayant un emploi non-trivial en complexité algorithmique.
LOVE 27/02/2019 Automatic Extraction of Malicious Behaviors, par Khanh-Huu-The Dam
Khanh-Huu-The Dam, LCR, LIPN, Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 15:00
Résumé :
The number of new malwares is increasing everyday. Thus malware detection is nowadays a big challenge. The existing techniques for malware detection require a huge effort of engineering to manually extract the malicious behaviors. To avoid this tedious task, we propose in this paper an approach to automatically extract the malicious behaviors. We model a program using an API call graph, and we represent the malicious behaviors using a malicious API graph. We then reduce the malicious behavior extraction problem to the problem of retrieving from the benign and malicious API call graphs the set of subgraphs that are relevant for malicious behaviors. We solve this issue by applying and adapting well-known efficient Information Retrieval techniques based on the TFIDF scheme. We use our automatically extracted malicious behavior specification for malware detection using a kind of product between graphs. We obtained interesting experimental results, as we get 99.04% of detection rate. Moreover, we were able to detect several malwares that well-known and widely used antiviruses such as Panda, Avira, Kaspersky, Avast, Qihoo- 360, McAfee, AVG, BitDefender, ESET-NOD32, F-Secure, and Symantec could not detect. This is a joint work with Tayssir Touili.
LOVE 27/02/2019 Integer-Complete Synthesis for Bounded Parametric Timed Automata, par Étienne André
Étienne André, LCR, LIPN, Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 16:30
Résumé :
Ensuring the correctness of critical real-time systems, involving concurrent behaviors and timing requirements, is crucial. Parameter synthesis aims at computing dense sets of valuations for the timing requirements, guaranteeing a good behavior. However, in most cases, the emptiness problem for reachability (i.e. whether there exists at least one parameter valuation for which some state is reachable) is undecidable and, as a consequence, synthesis procedures do not terminate in general, even for bounded parameters. In this paper, we introduce a parametric extrapolation, that allows us to derive an underapproximation in the form of linear constraints containing all the integer points ensuring reachability or unavoidability, and all the (non-necessarily integer) convex combinations of these integer points, for general PTA with a bounded parameter domain. Our algorithms terminate and can output constraints arbitrarily close to the complete result. Joint work with Didier Lime and Olivier H. Roux.
LOVE 27/02/2019 Les algèbres implicatives, d'après A. Miquel (1ère partie), par Luc Pellissier
Luc Pellissier, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
Les structures implicatives sont des structures algèbriques extrèmement simples généralisant à la fois les modèles dénotationnels du ?-calcul et les algèbres de Heyting. Elles permettent donc d'interpréter à la fois les termes et les types, qui se retrouvent ainsi identifiés. Les structures implicatives sont donc une fondation naturelle pour le forcing (où l'on interprète les formules dans des algèbres de Boole – dans le cas classique – ou de Heyting – dans le cas intuitionniste) et la réalisabilité (où l'on interprète les formules par des ensembles de ?-termes). On verra qu'en effet, une structure implicative munie d'un quotient adéquat engendre un tripos, c'est-à-dire un modèle de la logique intitutionniste d'ordre supérieure (imprédicative).
LOVE 27/02/2019 Les algèbres implicatives, d'après A. Miquel (2ème partie), par Luc Pellissier
Luc Pellissier, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
CÂ’est la suite, donc, on parlera de passoires https://www.youtube.com/watch?v=TMt6TDQe4nQ
LOVE 27/02/2019 Some interplays between proof theory and computational complexity, par Anupam Das
Anupam Das, LIP, ENS Lyon  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
Proof complexity is the branch of proof theory concerned with the size of proofs. Due to old and well-known results of Cook and Reckhow, many important questions about computational complexity are equivalent to natural problems in proof complexity. For instance, coNP = NP just if there is an 'efficient' proof system for classical propositional logic. I will survey a now well-developed line of work on the proof complexity of 'deep inference' systems which has culminated in several novel phenomena in proof complexity, including improved bounds for monotone proof systems. I will also discuss remaining open problems in the area and some of their consequences. A closely related area to proof complexity is bounded arithmetic, which studies weak fragments of arithmetic whose representable functions are typically feasible complexity classes, via bounds on quantifiers. They also act as uniform versions of corresponding propositional systems, forming a three-way correspondence. I will show how this methodology can be extended to certain deep inference and monotone systems via intuitionistic versions of bounded arithmetic, making use of a novel technique that combines the usual 'witness function method' of bounded arithmetic with realisability style extraction. I will further motivate the study of such theories in 'linear logic' in order to address the remaining correspondences, and present some recent work along this line. Finally I will present an upcoming research project that aims to unify various strands of this research in order to develop a comprehensive approach to monotone complexity classes.
LOVE 27/02/2019 Implémentation de complexité implicite dans les compilateurs, par Thomas Rubiano
Thomas Rubiano, LIPN, Université Paris 13  
Salle A303, bâtiment A, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
La complexité implicite s’intéresse à la gestion des ressources, temps ou espace, consommées par un programme. Comme les méthodes de complexité implicite fonctionnent à l’aide de critères purement syntaxiques, ces analyses peuvent être faites au moment de la compilation du programme (et pas au cours de son exécution) et le “certificat” obtenu peut alors être directement associé à l’exécutable. De plus, les compilateurs manipulent dans leurs représentations intermédiaires des langages proches de l’assembleur avec un accès au graphe de flot de contrôle. Ainsi, on dispose directement des outils nécessaires pour exprimer certaines méthodes de complexité implicite. Le but initial de la thèse était d’écrire, un plugin pour effectuer la détection de programmes qui calculent en espace constant (Non-Size-Increasing Programs) au cours de la compilation et en déduire automatiquement des optimisations d’allocation de mémoire. Le premier compilateur cible a été llvm, une passe a donc été implémentée. Ensuite, il était prévu d’une part de continuer à implémenter des méthodes de complexité implicite dans les compilateurs –notamment la Size Change Termination ou les polynômes mwp qui s’expriment bien sur un langage impératif de bas niveau. D’autre part, de chercher à exprimer d’autres analyses dans ce genre de langage afin de comparer de manière plus systématique les différentes analyses existantes. C'est en apprenant les techniques utilisées dans ces deux dernières théories que nous nous sommes intéressés à implémenter une optimisation de pelage de boucle présentée sur un langage WHILE dans un brouillon de Lars Kristiansen. Nous l'avons repris et baptisée: "Calcul de degré d'invariance et composition de commandes pour du pelage de boucle". Après avoir fait quelques tests sur le langage C à l'aide d'un parser « jouet » en python. Une passe LLVM est en cours de développement… Les analyses de complexité implicites sont actuellement décrites sur des langages « jouets ». En les portant sur des « vrais » langages de programmation, la thèse a pour but de fournir à la communauté un outil permettant de traiter une grande quantité d’exemples et d’avoir une idée plus précise de l’expressivité réelle de ces analyses. De plus elle crée un pont avec la communauté compilation afin que chacune apporte à l'autre. Cette thèse est financée par le projet ANR ELICA
LOVE 27/02/2019 Vers une théorie de la réécriture probabiliste, par Flavien Breuvart
Flavien Breuvart, LIPN, Université Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 11:00
Résumé :
Après une récapitulation des définitions fondamentales et enjeux de la théorie de la réduction de termes (TRS et HORS), nous allons nous poser la question de l'ajout de composantes probabilistes. Nous verrons que des problématiques importantes apparaissent à un niveau très élémentaire. En fait, elles apparaissent déjà au niveau des ARS (graphe orientés infinis décrivant une dynamique) qui sont extrêmement généraux et contiennent les automates dont la généralisation probabiliste a été abondamment étudiée. En utilisant ces travaux sur les automates, et plus généralement sur les co-algèbres, nous avons décrit un formalisme pouvant, nous l'espérons, traiter élégamment des problèmes de réécritures probabilistes.
LOVE 27/02/2019 Regular Model Checking: Vérification et systèmes de réécriture, par Tayssir Touili
Tayssir Touili, LIPN, Université Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
Nous nous intéressons dans cet exposé au model-checking des systèmes infinis, notamment les systèmes paramétrés et les programmes récursifs parallèles. Nous présentons un cadre uniforme pour la vérification algorithmique de ces systèmes. Ce cadre est basé sur la représentation des ensembles de configurations par des automates de mots ou d'arbres, et la représentation des relations de transition des systèmes par des règles de réécritures de mots ou de termes. Le problème de la vérification est ensuite réduit au calcul des ensembles des accessibles dans ce cadre.
LOVE 27/02/2019 Proving array-manipulating programs without arrays , par David Monniaux
David Monniaux, VERIMAG, Université de Grenoble  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 15:00
Résumé :
Automatically verifying safety properties of programs is hard. Many approaches exist for verifying programs operating on Boolean and integer values (e.g. abstract interpretation, counterexample-guided abstraction refinement using interpolants), but transposing them to array properties has been fraught with difficulties. Our work addresses that issue with a powerful and flexible abstraction that morphes concrete array cells into a finite set of abstract ones. This abstraction is parametric both in precision and in the back-end analysis used. One possible application would be distributed systems, where processes are modeled using arrays indexed by the process ID.
LOVE 27/02/2019 Approches pour la modélisation et vérification des systèmes temporisés en utilisant les diagrammes états-transitions et les réseaux de Petri colorés, par Mahdi Benmoussa
Mahdi Benmoussa, LCR, LIPN, Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 16:30
Résumé :
(Répétition avant soutenance de thèse.) Nous présentons dans ce travail de thèse des approches pour la spécification et la vérification des systèmes temporisés. La première partie concerne une méthode de spécification en utilisant les diagrammes états-transitions pour modéliser un système donné en partant d'une description textuelle. Elle comporte plusieurs étapes et utilise des observateurs d'états et des événements afin d'engendrer le diagramme états-transitions. Un outil qui implémente les différentes étapes de la méthode de spécification pour une application semi-automatique est présenté. La seconde partie concerne une traduction des diagrammes états-transitions vers les réseaux de Petri colorés, ce qui permet d'utiliser les méthodes de vérification. Nous prenons en considération dans cette traduction un ensemble important des éléments syntaxiques des diagrammes états-transitions, tels que la concurrence, la hiérarchie, etc. Un outil qui implémente la traduction pour un passage automatique des diagrammes états-transitions vers les réseaux de Petri colorés est en cours de développement. La dernière partie concerne l'intégration des contraintes temporelles dans les deux approches précédentes. Nous définissons des annotations pour les diagrammes états-transitions dont nous fournissons la syntaxe et la sémantique. Ces annotations seront ensuite utilisées dans la méthode de spécification et la traduction. Le but est de proposer des annotations faciles à comprendre et à utiliser avec une syntaxe qui prend en compte des contraintes parmi les plus utilisées.
LOVE 27/02/2019 Parametric model checking timed automata under non-Zenoness assumption, par Gia
Gia, Hoang Gia Nguyen  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 16:30
Résumé :
Real-time systems often involve hard timing constraints and concurrency, and are notoriously hard to design or verify. Given a model of a real-time system and a property, parametric model-checking aims at synthesizing timing valuations such that the model satisfies the property. However, the counter-example returned by such a procedure may be Zeno (an infinite number of discrete actions in a finite time), which is unrealistic. On the one hand, we show that synthesizing parameter valuations such that at least one counter-example run is non-Zeno is undecidable for Parametric Timed Automata (PTA). On the other hand, we propose a procedure based on a transformation of PTA into Clock Upper Bound PTA to derive such valuations.
LOVE 27/02/2019 What’s decidable about parametric timed automata?, par Étienne André
Étienne André, LCR, LIPN, Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 16:00
Résumé :
Parametric timed automata (PTA) are a powerful formalism to reason, simulate and formally verify critical real-time systems. After two decades of research on PTA, it is now well-understood that any non-trivial problem studied is undecidable for general PTA. We provide here a survey of decision and computation problems for PTA. On the one hand, bounding time, bounding the number of parameters or the domain of the parameters does not (in general) lead to any decidability. On the other hand, restricting the number of clocks, the use of clocks (compared or not with the parameters), and the use of parameters (e.g. used only as upper or lower bounds) leads to decidability of some problems.
LOVE 27/02/2019 Harnessing Malware Intelligence for Defense and Attribution, par Arun Lakhotia
Arun Lakhotia, University of Louisiana at Lafayette  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 14:00
Résumé :
The number of unique malware has been doubling every year for over two decades. The majority of effort in malware analysis has focused on methods for preventing malware infection. We view the exponential growth of malware as an underutilized source of intelligence. Given that the number of malware authors are not doubling each year, the large volume of malware must contain evidence that connects them. The challenge is how to extract the connections and do so in a timely manner to be useful. This talk will describe Cythereal MAGIC, a cloud-based malware analysis service, for mining large scale malware repositories. MAGIC, an offshoot of research conducted under the DARPA Cyber Genome program, uses malware "genome" to construct features that are resilient to many obfuscations. The correlations discovered by MAGIC can be used to prevent and detect zero-day malware. The correlations can also be used to investigate malware attacks for attribution.
LOVE 27/02/2019 CARET Model Checking For Pushdown Systems, par Huu-Vu Nguyen
Huu-Vu Nguyen, LCR, LIPN, Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 15:00
Résumé :
CARET (A temporal logic of calls and returns) was introduced by Alur et al. This logic allows to write linear temporal logic formulas while taking into account matching of calls and returns. However, CARET model checking for Pushdown Systems (PDSs) was never considered in the literature. Previous works only dealt with the model checking problem for Recursive State Machine (RSMs). While RSMs are a good formalism to model sequential programs written in structured programming languages like C or Java, they become non suitable for modeling binary or assembly programs, since, in these programs, explicit push and pop of the stack can occur. Thus, it is very important to have a CARET model checking algorithm for PDSs. We tackle this problem in this paper. We also consider CARET model checking with regular valuations, where the set of configurations in which an atomic proposition holds is a regular language. We reduce these problems to the emptiness problem of Büchi Pushdown Systems. We implemented our technique in a tool, and we applied it to different case studies. Our results are encouraging. In particular, we were able to apply our tool to detect several malwares. This is a joint work with Tayssir Touili.
LOVE 27/02/2019 Malware Detection Based On Graph Classification, par Khanh Huu The Dam
Khanh Huu The Dam, LCR, LIPN, Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 14:00
Résumé :
Malware detection is nowadays a big challenge. The existing techniques for malware detection require a huge effort of engineering to manually extract the malicious behaviors. To avoid this tedious task of manually discovering malicious behaviors, we propose in this paper to apply learning for malware detection. Given a set of malwares and a set of benign programs, we show how learning techniques can be applied in order to detect malware. For that, we use abstract API graphs to represent programs. Abstract API graphs are graphs whose nodes are API functions and whose edges represent the order of execution of the different calls to the API functions (i.e., functions supported by the operating system). To learn malware, we apply well-known learning techniques based on Random Walk Graph Kernel (combined with Support Vector Machines). We can achieve a high detection rate with only few false alarms (98.93% for detection rate with 1.24% of false alarms). Moreover, we show that our techniques are able to detect several malwares that could not be detected by well-known and widely used antiviruses such as Avira, Kaspersky, Avast, Qihoo-360, McAfee, AVG, BitDefender, ESET-NOD32, F-Secure, Symantec or Panda. This is a joint work with Tayssir Touili.
LOVE 27/02/2019 Syntaxe transcendentale: première lecture., par Christophe Fouqueré
Christophe Fouqueré, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
JY Girard, avec ses 3 articles sur la "syntaxe transcendentale", aborde la logique sous un angle à la fois philosophico-logique et sous un angle technique, pour aller au-delà de ce qui est fait jusqu'à présent: non seulement la logique linéaire propositionnelle mais encore le traitement de l'égalité donc du premier ordre. Modestement, je commencerai par présenter la partie technique, qui reprend et étend le modèle des réseaux de preuves, en présentant la représentation de MALL et des exponentielles.
LOVE 27/02/2019 Expérimenter un modèle de programmation fonctionnel, réactif et concurrent (à environnement global) compositionnel en OCaml., par Jean-Vincent Loddo
Jean-Vincent Loddo, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
Note: Il s'agit d'un groupe de travail informel et non d'une présentation. Abstract: OCaml est un langage nativement multi-paradigme, permettant un style de programmation fonctionnel, impératif et objet. Une librairie de processus légers (threads), fournie avec le langage et s'appuyant sur le système d'exploitation sous-jacent, permet d'ajouter à la liste précédente le style de programmation concurrent à mémoire partagée (ou environnement "global"). Or, cette variante du style concurrent paraît tellement difficile et source d'erreurs ("race conditions", "deadlocks", "resource starvation") qu'elle est souvent réputée impraticable. Ce constat a probablement influencé la recherche sur les paradigmes concurrents, qui s'est orientée, depuis la fin des années '70 et début '80, sur le modèle opposé des algèbres de processus, c'est-à-dire à environnement "local" ou échange de messages (CSP de Hoare 1985, CCS de Milner 1989, LOTOS ISO 1985). L'intérêt soulevé par les mémoires transactionnelles à partir des années 2000, témoigne toutefois d'un retour à la mode de l'environnement global dans un cadre de programmation multi-thread. Entre-temps, un autre style de programmation, très adapté aux programmes interactifs et typiquement avec interface graphique, le style "réactif" (ou programmation événementielle) a fait brèche dans la culture des programmeurs et le support de ce style est offert dans un nombre grandissant de langages "mainstream", impératifs ou fonctionnels. Tout cela peut s'ajouter et se combiner à l'ancienne notion de "promesse" ("future") proposée comme mécanisme de synchronisation de programmes hybrides fonctionnels-concurrents (Friedman & Wise 1976, Baker & Hewitt 1977). Dans cet exposé nous présenterons une tentative de synthèse des styles fonctionnel, réactif et concurrent à environnement global, qui soit compositionnelle, c'est-à-dire permettant de composer des éléments modulaires. Cette solution, qui prend la forme contingente d'une librairie OCaml, a été inspirée par l'implémentation courante du logiciel Marionnet (simulateur de réseaux TCP/IP) et devrait, à terme, permettre la ré-implantation d'une partie critique du code.
LOVE 27/02/2019 Reachability Analysis of Pushdown Systems with an Upper Stack, par Adrien Pommellet
Adrien Pommellet, LCR, LIPN, Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 15:00
Résumé :
Pushdown systems (PDSs) are a natural model for sequential programs, but they can fail to accurately represent the way an assembly stack actually operates. Indeed, one may want to access the part of the memory that is below the current stack or base pointer, hence the need for a model that keeps track of this part of the memory. To this end, we introduce pushdown systems with an upper stack (UPDSs), an extension of PDSs where symbols popped from the stack are not destroyed but instead remain just above its top, and may be overwritten by later push rules. We prove that the sets of successors post* and predecessors pre* of a regular set of configurations of such a system are not always regular, but that post* is context-sensitive, so that we can decide whether a single configuration is forward reachable or not. In order to underapproximate pre* in a regular fashion, we consider a bounded-phase analysis of UPDSs, where a phase is a part of a run during which either push or pop rules are forbidden. We then present a method to overapproximate post* that relies on regular abstractions of runs of UPDSs. Finally, we show how these approximations can be used to detect stack overflows and stack pointer manipulations with malicious intent.
LOVE 27/02/2019 Introduction à la théorie de la complexité géométrique, d'après K. Mulmuley, par Luc Pellissier
Luc Pellissier, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
La théorie de la complexité géométrique est un programme de recherche porté par Ketan Mulmuley, qui vise à résoudre des questions de complexité après les avoir traduites comme des inclusions de surfaces algébriques représentant des groupes de symétries. Après avoir présenté la théorie avec beaucoup de recul, on présentera un résultat de séparation obtenu ainsi (entre P et une classe ad hoc).
LOVE 27/02/2019 Retrofitting linear types, par Arnaud Spiwack
Arnaud Spiwack, Tweag I/O  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
Type systems based on linear logic and their friends have proved that they are both capable of expressing a wealth of interesting abstractions. Among these the ability to mix garbage-collected and explicitly managed data in the same language. This is of prime interest for distributed computations that need to reduce latency induced by GC pauses: a smaller GC heap is a happier GC heap. I had always had the belief that to add linear types to a language was a rather intrusive procedure and that a language with linear types would basically be an entirely new language. The Rust language is a case in point: it has a linear-like type system, but it's a very different language from your run-of-the-mill functional language. This turns out not to be the case: this talk presents a way to extend a functional programming language. We are targeting Haskell but there is little specific to Haskell in this presentation. I will focus mostly on the type system and how it can be generalised: among other things the type system extends to dependent types.
LOVE 27/02/2019 Hybride Modelling, Analysis and Quantitative Verification of Large Biological Regulatory Networks, par Louis Fippo Fitime
Louis Fippo Fitime, LCR, LIPN, Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 11:30
Résumé :
Biological Regulatory Networks (BRNs) are usually used in systems biology for modelling, understanding and controlling the dynamics of different biological functions (differentiation, proliferation, proteins synthesis, apoptose) inside cells. Those networks are enhanced with experimental data that are nowadays more available which give an idea on the dynamics of BRNs components. Formal analysis of such models fails in front of the combinatorial explosion of generated behaviours despite the fact that BRNs provide abstract representation of biological systems. This thesis handles hybrid modelling, the simulation, the formal verification and control of Large Biological Regulatory Networks. This modelling is done thanks to stochastic automata networks, thereafter to Process Hitting by integrating time-series data. Firstly, this thesis proposes a refining of the dynamics by estimation of stochastic and temporal (delay) parameters from time-series data and integration of those parameters in automata networks models. This integration allows the parametrisation of the transitions between the states of the system. Then, a statistical analysis of the traces of the stochastic simulation is proposed to compare the dynamics of simulations with the experimental data. Secondly, this thesis develops static analysis by abstract interpretation in the automata networks allowing efficient under- and over-approximation of quantitative (probability and delay) reachability properties. This analysis enables to highlight the critical components to satisfy these properties. Finally, taking advantage from the previous developed static analyses for the reachability properties in the qualitative point of view, and from the power of logic programming (Answer Set Programming), this thesis addresses the domain of control of system by proposing the identification of bifurcation transitions. Bifurcations are transitions after which the system can no longer reach a state that was previously reachable.
LOVE 27/02/2019 Preserving Partial Order Runs in Parametric Time Petri Nets, par Cesar Rodriguez
Cesar Rodriguez, LCR, LIPN, Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 16:30
Résumé :
Parameter synthesis for timed systems aims at deriving parameter valuations satisfying a given property. In this paper we target concurrent systems; it is well known that concurrency is a source of state-space explosion, and partial order techniques were defined to cope with this problem. Here we use partial order semantics for parametric time Petri nets as a way to significantly enhance the result of an existing synthesis algorithm. Given a reference parameter valuation, our approach synthesizes other valuations preserving, up to interleaving, the behavior of the reference parameter valuation. We show the applicability of our approach using acyclic asynchronous circuits. Join work with Thomas Chatain and Étienne André.
LOVE 27/02/2019 Des preuves, oui, mais formelles !, par Micaela MAYERO
Micaela MAYERO, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
Dans cet exposé, très informel, lui, je parlerai de l'évolution des outils de preuves formelles ces 20, voire ces 30, dernières années. Nous nous appuierons sur quelques exemples afin de montrer comment les formalisations contribuent à la fois au développement de ces outils via des avancés théoriques majeurs ainsi qu'aux domaines qui s'engagent peu à peu dans leur utilisation. Suite à une première partie accessible à tout public, nous parlerons de la logique sous-jacente à l'un des système connaissant le plus d'avancées et de changements: Coq. Nous aborderons les évolutions de la théorie des types avec (im)prédicativité, la logique classique avec le choix de la totalité et d'autres avancées, pour finir, si nous avons le temps, par quelques mots sur CoqHoTT et l'axiome d'univalence.
LOVE 27/02/2019 Syntaxe transcendentale: seconde lecture., par Christophe Fouqueré
Christophe Fouqueré, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
Suite de la première lecture: JY Girard, avec ses 3 articles sur la "syntaxe transcendentale", aborde la logique sous un angle à la fois philosophico-logique et sous un angle technique, pour aller au-delà de ce qui est fait jusqu'à présent: non seulement la logique linéaire propositionnelle mais encore le traitement de l'égalité donc du premier ordre. Modestement, je commencerai par présenter la partie technique, qui reprend et étend le modèle des réseaux de preuves, en présentant la représentation de MALL et des exponentielles.
LOVE 27/02/2019 Équivalences entre programmes, par Jean-Yves Moyen
Jean-Yves Moyen, LIPN - University of Copenhagen  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
Partant du théorème de Rice, on définit l'équivalence extensionelle comme "deux programmes sont équivalents si ils calculent la même fonction." Le théorème de Rice stipule alors une indécidabilité forte de cette équivalence (aucune union de classes n'est décidable). Qu'en est-il des autres équivalences entre programmes ? Certaines sont décidables (eg, avoir le même nombre de lignes de codes), d'autres non. L'ensemble des équivalences possède une structure de treillis complet et le théorème de Rice parle de l'indécidabilité d'un filtre principal de ce treillis. À partir de ces constatations, j'explore deux pistes parallèles. D'une part, quelle est l'importance de l'équivalence extensionelle dans ces résultats ? Est-ce qu'on peut obtenir d'autres résultats similaires à partir d'une autre équivalence ? D'autre part, comment étudier l'ensemble du treillis des équivalences ? Est-ce qu'on peut trouver des sous-ensembles qui conservent la structure lié à l'ordre tout en étant plus facilement manipulables (notamment, dénombrables) ?
LOVE 27/02/2019 Why complexity theorists should care about philosophy, par Thomas Seiller
Thomas Seiller, University of Copenhagen (DIKU)  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
Theoretical computer science was somehow born almost a hundred years ago when logicians asked themselves the question: "What is a computable function?". This question, purely theoretical, was answered before the first computer was designed, in the form of the Church-Turing thesis: a computable function is one that can be defined in one of the following equivalent models: recursive functions, Turing machines, or lambda-calculus. The apparition of actual computing devices however made it clear from the start that another question made more sense for practical purposes, namely: "What is an *efficiently* computable function?". This question was tackled by three different work in the span of a single year, marking the birth of computational complexity. Nowadays, computational complexity is an established field: many methods and results have been obtained, and the number of complexity classes grows every year. However, a number of basic open problems remain unanswered, in particular concerning classification of complexity classes. Even worse than that, a number of results – called barriers – show that no known method will succeed in producing a new separation result, i.e. show that two classes (e.g. P and NP, or L and P) are disjoint. From a purely theoretical point of view, this lack of methods might be explained by a historic tradition of viewing programs as functions. Once this misconception identified, it points to a lack of adequate foundations for the theory of computation. Fortunately, some recent technical developments may provide a solution to this problem.
LOVE 27/02/2019 Monades et comonades (suite), par Flavien Breuvart
Flavien Breuvart, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
Dans cette deuxième séance du GdT modades et comonades, je présenterais les monades et comonades gradées. J'insisterais, en particulier, sur ma vision de ces objets comme potentielle piste pour faire interagir interprétation abstraite et typage dans les langages fonctionnels.
LOVE 27/02/2019 Directed homology theories for geometric models of true concurrency, par Jérémy Dubut
Jérémy Dubut, ENS Cachan  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
Studying a system through its geometry is the main purpose of directed algebraic topology. This topic emerged in computer science, more particularly in true concurrency, where Pratt introduced his higher dimensional automata (HDA) in 1991 (actually, the idea of geometry of concurrency can be tracked down Dijkstra in 1965). Those automata are geometric by nature: every set of n processes executing independent actions can be modeled by a n-cube, and such an automata then gives rise to a topological space, obtained by glueing such cubes together, with a specific direction of time coming from the execution flow. It then seems natural to use tools from algebraic topology to study those spaces: paths model executions, homotopies of paths, that is continuous deformations of paths, model equivalence of executions modulo scheduling of independent actions, and so on, but all those notions must preserve the direction somehow. This brings many complications and the theory must be done again, essentially from scratch. In this talk, after developing this idea of geometry of true concurrency, I will focus on homology. Homology is a nice computable tool from algebraic topology and it is a challenge in directed algebraic topology to find a satisfactory analogue that behaves well with direction. I will present our candidate of `directed homologyÂ’, called natural (or bimodule) homology. This object consists in a functor with values in modules, which looks at the classical homology of trace spaces (a nice abstraction of what we may call `space of executionsÂ’) and how those homologies evolve with time. This evolution can be studied through an abstract notion of bisimulation of functors with values in modules, that has many equivalent characterizations (using relations, using lifting properties, using Grothendieck construction, Â…) and whose existence is decidable in simple cases. Finally, among nice properties of our directed homology, I will show you that it is computable on simple spaces, which are already enough to model simple truly concurrent systems. Joint work with Eric Goubault and Jean Goubault-Larrecq.
LOVE 27/02/2019 An interpretation of system F through bar recursion, par Valentin Blot
Valentin Blot, Queen Mary University of London  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
There are two possible computational interpretations of second-order arithmetic: Girard's system F or Spector's bar recursion and its variants. While the logic is the same, the programs obtained from these two interpretations have a fundamentally different computational behavior and their relationship is not well understood. We make a step towards a comparison by defining the first translation of system F into a simply-typed total language with a variant of bar recursion. This translation relies on a realizability interpretation of second-order arithmetic. Due to Gödel's incompleteness theorem there is no proof of termination of system F within second-order arithmetic. However, for each individual term of system F there is a proof in second-order arithmetic that it terminates, with its realizability interpretation providing a bound on the number of reduction steps to reach a normal form. Using this bound, we compute the normal form through primitive recursion. Moreover, since the normalization proof of system F proceeds by induction on typing derivations, the translation is compositional. The flexibility of our method opens the possibility of getting a more direct translation that will provide an alternative approach to the study of polymorphism, namely through bar recursion.
LOVE 27/02/2019 Bar-récursion, analyse et réalisabilité classique, par Hadrien Batmalle
Hadrien Batmalle, IRIF  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
La réalisabilité classique est une théorie née des travaux de Jean-Louis Krivine dans les années 1990, à la frontière entre la logique et l'informatique théorique. Côté informatique, elle offre un cadre adapté à l'interprétation calculatoire de preuves classiques. Côté logique, elle apparaît comme une généralisation prometteuse du forcing de Cohen. À un modèle du lambda-calcul, on peut ainsi associer un modèle de la théorie des ensembles ZF. On s'intéresse ici à des modèles de programmation vérifiant une propriété de continuité: il peut s'agir de modèles basés sur les domaines de la sémantique dénotationnelle, ou bien de modèles de termes d'une version infinitaire du lambda-calcul. Dans ces modèles, l'instruction 'quote' (qu'on utilise usuellement en réalisabilité classique pour interpréter l'axiome du choix dépendant) n'est pas disponible. On utilise donc la technique de la bar-récursion pour interpréter l'axiome du choix dépendant. Or (en considérant la réalisabilité classique comme une généralisation du forcing), il apparaît que la bar-récursion est de plus l'analogue de la condition de chaîne descendante dans les algèbres de forcing (qui correspond à une propriété de préservation des réels). On obtient alors que toute formule de l'analyse vraie dans le modèle ambiant est réalisée dans ces nouveaux modèles, ce qui nous amène à la question suivante: quel est le comportement des programmes réalisant des formules de l'analyse?
LOVE 27/02/2019 Petite introduction à la logique catégorique, par Damiano Mazza
Damiano Mazza, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
On entend dire parfois que le lambda-calcul est "le langage interne des catégories cartesiennes fermées". Le "langage interne" d'une catégorie est une notion très générale (mais, à vrai dire, pas tout à fait formelle) de logique catégorique. Dans cet exposé, j'introduirai les concepts de base pour comprendre cette notion et expliquer comment elle est reliée à la sémantique dénotationnelle.
LOVE 27/02/2019 Inductive and Functional Types in Ludics, par Alice Pavaux
Alice Pavaux, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
Ludics is a logical framework in which types/formulas are modelled by sets of terms with the same computational behaviour. We investigate the representation of inductive data types and functional types in ludics. We study their structure following a game semantics approach. Inductive types are interpreted as least fixed points, and we prove an internal completeness result giving an explicit construction for such fixed points. The interactive properties of the ludics interpretation of inductive and functional types are then studied. In particular, we identify which higher-order functions types fail to satisfy type safety, and we give a computational explanation.
LOVE 27/02/2019 Partiality and container monads, par Niccolò Veltri
Niccolò Veltri, TTÃœ Küberneetika Instituut  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
We investigate monads of partiality in Martin-Löf type theory, following Moggi’s general monad-based method for modelling effectful computations. These monads are often called lifting monads and appear in category theory with different but related definitions. In this talk, we unveil the relation between containers and lifting monads. We show that the lifting monads usually employed in type theory can be specified in terms of containers. Moreover, we give a precise characterization of containers whose interpretations carry a lifting monad structure. We show that these conditions are tightly connected with Rosolini’s notion of dominance. We provide several examples, putting particular emphasis on Capretta’s delay monad and its quotiented variant, the non-termination monad.
LOVE 27/02/2019 Coherence for skew near-semiring categories, par Tarmo Uustalu
Tarmo Uustalu, Tallinn University of Technology  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
We consider skew near-semiring categories, a relaxation of near-semiring categories where the unitors, associators, annihilator and distributor are not required to be natural isomorphisms, they are just natural transformations in a particular direction. We prove a coherence theorem for such categories. The theorem states that, in a free skew near-semiring category over a set of objects, any two maps between an object and an object in normal form are equal. Our main motivating examples for skew near-semiring categories are from programming with effects. While (relative) monads and lax monoidal functors are the same as skew monoids in particular skew monoidal categories, (relative) MonadPlus and Alternative instances are skew near-semiring objects. This is joint work with Mauro Jaskelioff, Exequiel Rivas and Niccolò Veltri.
LOVE 27/02/2019 Réseaux de preuve pour MLL+Mix et algorithmes sur les graphes arêtes-coloriés, par Nguy?n Lê Thành D?ng
Nguy?n Lê Thành D?ng, Education national (future LIPN ?)  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
Le critère de correction de Danos-Regnier mène à poser le problème d'algorithmique des graphes suivant : étant donné un graphe apparié, trouver un cycle (ou un chemin) passant au plus une fois par chaque paire. Ce problème a été traité en théorie des graphes sous la forme plus générale de graphes munis d'une coloration sur leurs arêtes ("edge-colored graphs") ; la solution fait intervenir une réduction aux couplages parfaits et rejoint donc le travail de C. Retoré sur les "handsome proof-nets". Partant de cela, on obtient facilement d'une part un critère de correction pour MLL+Mix en temps linéaire, et d'autre part que le problème de correction des réseaux MLL+Mix est probablement plus difficile que celui pour MLL sans la règle Mix (qui est NL-complet). Ce dernier résultat explique que la littérature sur les critères de correction pour MLL+Mix soit plus maigre que celle pour MLL. Nous verrons également d'autres conséquences de ces liens entre logique linéaire et théorie des graphes, notamment en lien avec le graphe de dépendances d'un réseau introduit par Bagnol, Doumane et Saurin.
LOVE 27/02/2019 Circular Proofs for Subtyping and Termination, par Rodolphe Lepigre
Rodolphe Lepigre, Université de Savoie  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
In a recent (submitted) work with Christophe Raffalli, we designed a rich type system for an extension of System F with subtyping. It includes primitive sums and products, existential types, and (co-)inductive types. Using a combination of (pointed) subtyping and circular proofs, we were able to express the system with typing and subtyping rules that are syntax-directed (up to circularity). During my talk, I will try to give you a flavour of the techniques we used. In particular, I will show how choice operators can be used to get rid of typing contexts, and to allow the commutation of quantifiers with other connectives. I will then introduce the circular proof framework that is used for handling inductive and co-inductive types in subtyping rules, and general recursion in typing rules.
LOVE 27/02/2019 Smooth models of Differential Linear Logic, par Marie Kerjean
Marie Kerjean, IRIF  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
Differential Linear Logic was constructed following a study of discrete vectorial models of Linear Logic. We want to extend the semantics of Linear Logic in the natural domain of continuous objects and analysis. From the basic fact that Seely's formulas is the direct interpretation of the Kernel Theorem for distributions, we explain two developments : On one hand we axiomatize a Smooth Differential Linear Logic with a graded syntax where to each solvable Linear partial differential equation one associate an exponential. We construct a model of nuclear Fréchet/ Df spaces for this syntax. On the other hand, we argue that the interpretation of the $\parr$ as Schwartz's epsilon product should be the cornestone of the construction of a smooth classical model of DiLL. From a first-model of $k$-reflexive spaces, and based on pioneering works by Kriegl, Michor and Meise, we construct a variety of (at least two) new models of DiLL. This part is joint work with Y. Dabrowski.
LOVE 27/02/2019 Inlining après l'élimination de fermeture pour OCaml, par Pierre Chambart
Pierre Chambart, OCamlPro  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
Usuellement, dans les langages de haut niveau, l'inlining est fait sur un langage intermédiaire proche d'un lambda calcul, où celà revient pour les cas simple à de la beta-réduction. Pour diverses raisons, dans OCaml, nous avons décidé d'introduire un autre langage intermédiaire où les fermetures sont explicite (flambda) sur lequel les optimisations haut niveau sont effectuées. Nous discuterons des avantages et complexités qui viennent avec ce choix.
LOVE 27/02/2019 Formal language theory beyond trees and forests , par Tobias Heindel
Tobias Heindel, University of Copenhagen  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 16:30
Résumé :
The talk presents the theorems of Myhill-Nerode and Chomsky-Schützenberger, replacing trees and words by rewriting diagrams of semi-Thue systems, which are the paradigm example of planar acyclic circuit diagrams (PLACIDs)---the “graphical syntax” of monoidal categories. The talk will focus on the proposal of a definition of recognizable language in monoidal categories, namely sets of arrows that coincide with the inverse image of their direct image under a monoidal functor to a finite monoidal category. For the case of PLACIDs, this class of languages is shown to coincide with the languages of automata in the sense of Bossut, under modest assumptions on gates of circuit diagrams; moreover, the usual notion of recognizable tree language is recovered. The talk presents the Myhill-Nerode theorem as a tool for solving Bossut's open problem of automata complementation. The remainder of the talk describes work in progress and future work, in particular the Chomsky-Schützenberger theorem for PLACIDs.
LOVE 27/02/2019 A discussion on the conjectures NP vs PSPACE and NP vs coNP, par Hermann Hauesler
Hermann Hauesler , PUC-Rio  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
The aim of this talk is to open a discussion on the justification of the conjectures NP = coNP and NP = PSPACE by means of purely proof-theoretical arguments.
LOVE 27/02/2019 [soutenance] , par Thomas Rubiano
Thomas Rubiano, LIPN  
TBA
27/02/2019    15:22 - 13:00
Résumé :
LOVE 27/02/2019 Réduction et Approximations Linéaires , par Luc Pellissier
Luc Pellissier, LIPN  
TBA
27/02/2019    15:22 - 17:00
Résumé :
TBA
LOVE 27/02/2019 Séminaire SV : Fadwa Rekik, par Fadwa Rekik
Fadwa Rekik, ATER à Galilée  
Salle A303, bâtiment A, campus de Villetaneuse
27/02/2019    15:22 - 16:00
Résumé :
L’architecture orientée service (SOA) est un paradigme qui offre des mécanismes permettant une grande flexibilité des architectures des systèmes logiciels tout en réduisant leurs coûts de développement puisqu’elle se base sur des entités modulaires et réutilisables appelées services. Ces services peuvent être réutilisés dans le cadre d’une composition ou d’une chorégraphie de services pour la construction de nouveaux processus métiers transverses. De son côté, le paradigme de l’Ingénierie Dirigé par les Modèles (IDM) offre au travers de ses deux principes fondateurs, l’abstraction et l’automatisation, deux moyens puissants de gestion de la complexité sans cesse croissante des systèmes. Combiner les deux paradigmes et concevoir ainsi une approche de type SOA dirigée par les modèles semble une piste prometteuse. Cependant, malgré les progrès de l’application des principes de l’IDM la spécification et le développement des applications SOA, plusieurs problèmes restent à résoudre. Un de ces problèmes est d’effectuer une vérification rigoureuse des modèles de spécification des applications orientées services. Ces modèles sont généralement composés de plusieurs vues sémantiquement liées les unes aux autres. Un deuxième problème est la transformation de ces modèles de spécification en code exécutable. En particulier, les chorégraphies de service doivent être transformées en orchestrations exécutables tout en préservant la sémantique des scénarios de haut niveau décrits par ces chorégraphies et en tenant compte des aspects critiques inhérents aux systèmes distribués tels que l’asynchronisme. La vérification de l'exécution est aussi nécessaire afin de détecter les comportements erronés lors de l’exécution. Pour relever ces défis, nous proposons une approche SOA dirigée par les modèles qui repose sur le standard OMG SoaML. Lors de la spécification, la cohérence des modèles SoaML est vérifiée en utilisant la validation statique des modèles moyennant des règles OCL que nous avons définies. Nous avons spécifié également des règles de transformation pour permettre la génération automatique d'artefacts exécutables. Enfin, nous avons défini un cadre de test à base de modèles pour vérifier la conformité de l’exécution des chorégraphies de services, incluant les orchestrateurs générés, aux modèles de spécification. L'ensemble de notre méthode a été outillé en extension de l’outil de modélisation UML, Papyrus, et de l’outil d’analyse formelle, Diversity.
LOVE 27/02/2019 Séminaire SV : Hiba Ouni, par Hiba Ouni
Hiba Ouni  
Salle A303, bâtiment A, campus de Villetaneuse
27/02/2019    15:22 - 16:00
Résumé :
Titre : Parallel Symbolic Observation Graph Abstract: Model checking is a powerful technique for verifying and analyzing complex systems in many application fields. The analysis process of complex and concurrent systems often requires large computation resources which represents a real challenge. Even with simple configurations, the well-known state explosion problem is faced as the generated state space of such systems grows exponentially with the number of the system components. Numerous methods and techniques have been developed to overcome this problem including parallel and distributed-memory processing. In this work, we aim at improving the performances of the so called Symbolic Observation Graph (SOG) construction by using parallelization techniques. A SOG is a hybrid structure where the transitions of a system are divided into observed and unobserved ones. The nodes of this graph are then defined as sets of states linked with unobserved transitions (and encoded symbolically with a BDD) and edges are labeled with observed transitions only (and are explicitly represented). We propose two parallel algorithms to build the SOG. The first algorithm is dedicated for shared memory architectures, and is based on the distribution of the SOG construction on several threads using a dynamic load balancing scheme. The second algorithm is proposed for distributed memory architectures, and distributes the SOG construction on processes using a static load balancing scheme. These two algorithms are implemented and their performances are studied and compared to each other and to the sequential construction of the SOG.
LOVE 27/02/2019 A unified framework for notions of algebraic theory, par Soichiro Fujii
Soichiro Fujii, NII Tokyo  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 18:30
Résumé :
Universal algebra uniformly captures various algebraic structures, by expressing them as equational theories or (abstract) clones. The ubiquity of algebraic structures in mathematics has also given rise to several variants of universal algebra, such as symmetric and non-symmetric operads, clubs, and monads. In this talk, I will present a unified framework for these cousins of universal algebra, or notions of algebraic theory. First I will explain how each notion of algebraic theory can be identified with a certain monoidal category, in such a way that theories correspond to monoids. Then I will introduce a categorical structure underlying the definition of models of theories. In specific examples, it often arises in the form of oplax action or enrichment. Finally I will uniformly characterize categories of models for various notions of algebraic theory, by a double-categorical universal property in the pseudo-double category of profunctors.
LOVE 27/02/2019 Probabilistic Rewriting, par Claudia Faggian
Claudia Faggian, IRIF  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
We investigate how techniques from Rewrite Theory can help us to study calculi whose evaluation is both probabilistic and non-deterministic (think untyped probabilistic lambda-calculus, in which non-determinism arises from choosing between different redexes). We are interested in relations between week and strong normalization, and whatever the result is unique. In particular, we characterize the properties “non-determinism is irrelevant” and “strategy A is always better than strategy B”. As an application, it turns out that probabilistic lambda-calculus equipped with weak call-by-value reduction has striking properties.
LOVE 27/02/2019 Des Preuves Syntactiques aux Preuves Combinatoires, par Matteo Acclavio
Matteo Acclavio, LIX  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
Dans cet exposé nous allons étudier les preuves combinatoires de Hughes comme notion de identité de preuve pour la logique classique. Nous montrons comment divers formalismes, notamment le caclulus des sequents, les tableaux analytiques et la résolution, peuvent être traduits en preuves combinatoires, et quelle notion d'identité ils appliquent. (Joint work with Lutz Strassburger)
LOVE 27/02/2019 Gdt Complexité suite, par Paulin de Naurois
Paulin de Naurois, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
Suite du premier gdt
LOVE 27/02/2019 Un calcul des séquents avec des types dépendants pour l'arithmétique classique, par Etienne MIQUEY
Etienne MIQUEY, Gallinette (Nantes)  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 13:00
Résumé :
En 2012, Hugo Herbelin définit dPA?, un langage typé qui fournit, dans un cadre compatible avec la logique classique, un terme de preuve pour l’axiome du choix dépendant, qui peut être vu comme une adaptation de la preuve constructive de l’axiome du choix en théorie des types de Martin-Löf ou une internalisation dans un système de preuve de l’approche en réalisabilité de Berardi, Bezem et Coquand. Malheureusement ce calcul ne dispose pas d'une preuve de normalisation, la difficulté d'une telle preuve est liée à la présence simultanée de types dépendants (pour la partie constructive du choix), d'opérateurs de contrôle (pour la logique classique), d'objets co-inductifs (pour "encoder" les fonctions de type N ? A par des streams (a?,a?,...)) et d'évaluation paresseuse avec partage (pour ces objets co-inductifs). Durant cet exposé, nous verrons comment définir une variante de dPA? en calcul des séquents dont on pourra prouver la correction. Au passage, on montrera la normalisation du call-by-need classique (présenté comme une extension du ?µµ?-calcul avec des environnements partagés) en utilisant notamment des techniques de réalisabilité à la Krivine ; et l'on développera un calcul des séquents classique avec types dépendants, dont la correction est prouvable à l'aide d'une traduction CPS tenant compte des dépendances.
LOVE 27/02/2019 Session-based concurrency, reactively, par Mauricio Cano
Mauricio Cano  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
This talk concerns formal models for the analysis of communication/centric software systems that feature declarative and reactive behaviors. We focus on session-based concurrency, the interaction model induced by session types, which uses (variants of) the pi-calculus as specification languages. While well-established, such process models are not expressive enough to specify declarative and reactive behaviors common in emerging communication-centric software systems. Here we propose the synchronous reactive programming paradigm (SRP) as a uniform foundation for session-based concurrency. We present correct encodings of session-based calculi into ReactiveML, a synchronous reactive programming language. Our encodings bridge the gap between process specifications and concurrent programs in which session-based concurrency seamlessly coexists with declarative, reactive, timed, and contextual behaviors.
LOVE 27/02/2019 Coends and proof equivalence in MLL2, par Paolo Pistone
Paolo Pistone  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 13:00
Résumé :
> Proof nets provide permutation-independent representations of proofs and are used to investigate coherence problems for monoidal categories. We investigate a coherence problem concerning Second Order Multiplicative Linear Logic MLL2, that is, the one of characterizing the equivalence over proofs generated by the interpretation of quantifiers by means of ends and coends. This equivalence is naturally induced by the usual second order translation of multiplicative units and connectives and is related to the investigations on the parametric models of System F. > By adapting the "rewiring approach" used in the proof net characterization of the free *-autonomous category, we provide a compact representation of proof nets for a fragment of MLL2 related to the Yoneda isomorphism. We prove that the equivalence generated by coends over proofs in this fragment is fully characterized by the rewiring equivalence over proof nets.
LOVE 27/02/2019 Definable Ellipsoid Method, Sums-of-Squares Proofs, and the Graph Isomorphism Problem, par Joanna Ochremiak
Joanna Ochremiak  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:30
Résumé :
The isomorphisms between two graphs can be described by the solutions of a system of polynomial inequalities and equations. We analyse the relative power of different proof systems which can be used to certify that a system corresponding to a pair of non-isomorphic graphs has no solution. Our results complete a full cycle of implications to show that, for the graph isomorphism problem, the Sherali-Adams, Polynomial Calculus and Sums-of-Squares proof systems are equally powerful, up to a constant loss in the degree. We prove this statement purely about the relative strength of proof systems through an excursion into the descriptive complexity of the ellipsoid method and bounded-variable infinitary logics. This is joint work with Albert Atserias.
LOVE 27/02/2019 CoGITARe, par Flavien Breuvart
Flavien Breuvart, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 11:45
Résumé :
Mon ARNJCJC CoGITARe a été accepté cet été. Ce séminaire a pour but de présenter le projet, ses objectifs et ses différentes facettes en essayant de rester haut niveau.
LOVE 27/02/2019 A UML-based Proposal for IoT System Requirements Specification, par Gianna Reggio
Gianna Reggio, DIBRIS – Università di Genova, Italy  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 16:00
Résumé :
The talk presents a preliminary version of IotReq, a method for the elicitation and specification of the requirements for an IoT system. The first task suggested by IotReq is the modelling of the domain, using the UML and following the service-oriente d paradigm, then the goals of the IoT system to build are elicited and specified, again using the UML and extending the domain model, producing a specification of the functional requirements. IotReq also provides preliminary indications for specifying the technological nonfunctional requirements. A case study, the specication of the requirements for a system to support the GenoaÂ’s Science Festival is presented too.
LOVE 27/02/2019 One-Sided Communications for more Efficient Parallel State Space Exploration over RDMA Clusters , par Sami Evangelista
Sami Evangelista, LIPN, Équipe LoVe  
Salle A303, bâtiment A, Université de Villetaneuse
27/02/2019    15:22 - 16:00
Résumé :
This talk presetns the use of one-sided communications in the context of state space exploration. This operation is often the core component of model checking tools that explores a system state space to look for behaviours deviating from its specification. It basically consists in the exploration of a (usually huge) directed graph whose nodes and edges represent respectively system states and system changes. We revisit the state of the art distributed algorithm and adapt it to RDMA clusters with an implementation over the OpenSHMEM library and report on preliminary experiments conducted on the Grid'5000 cluster. This asynchronous approach thus reduces the significant communication costs induced by process synchronisation in two-sided communications.
LOVE 27/02/2019 GdT : SL=L, par Paulin
Paulin, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 11:30
Résumé :
groupe de travail sur le résultat d'égalité de classes SL=L (Annonce très tardive car oubliée, désolé...)
LOVE 27/02/2019 GADTs , par Flavien
Flavien, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 15:30
Résumé :
Il s'agit d'une présentation général des GADTs par Flavien, avec une explication de leurs intérêts pratique. Cela sera suivit d'un cas d'étude présenté par Jean-Vincent sur lequel on pourra réfléchir tous ensemble. Le créneau est long, car on ira manger entre les deux parties.
LOVE 27/02/2019 Arrows , par Exequiel Rivas
Exequiel Rivas, Irif  
Salle A303, bâtiment A, Université de Villetaneuse
27/02/2019    15:22 - 17:00
Résumé :
Using monads for structuring computational effects had a big impact in the functional programming community. Arrows (Hughes 2000) are a generalisation of monads which provides support for computational effects that may be partially static. This talk will begin with an introduction on the subject, and then continue to discuss one the possible semantics of arrows from a categorical perspective.
LOVE 27/02/2019 Soft modalities as prices: a game model for intuitionistic linear logic with subexponentials, par Carlos Olarte
Carlos Olarte, Universidade Federal do Rio Grande do Norte  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
We look at substructural calculi from a game semantic point of view, guided by certain intuitions about resource conscious and, more specifically, cost conscious reasoning. To this aim, we start with a game for aILL (affine intuitionistic linear logic), where player I defends a claim corresponding to a (single-conclusion) sequent, while player II tries to refute that claim. Branching rules for additive connectives are modeled by choices of II, while branching for multiplicative connectives leads to splitting the game into parallel subgames, all of which have to be won by player I to succeed. The game comes into full swing by using subexponentials for representing two types of options - volatile and permanent - for purchasing resources. This leads to a new type of subexponetial calculus where costs are attached to sequents. Different proofs are interpreted as more or less expensive strategies to obtain a certain resource from a bunch of resources (priced options). Finally, we generalize the concept of costs and option's prices in proofs by using a semiring structure. This general framework allows us to interpret a wider range of subexponential systems and give meaning to the use of resources in proofs in a more flexible way.
LOVE 27/02/2019 State Compression Based on One-Sided Communications for Distributed Model Checking, par Laure Petrucci
Laure Petrucci, LIPN, Équipe LoVe  
Salle A303, bâtiment A, Université de Villetaneuse
27/02/2019    15:22 - 16:00
Résumé :
We propose a distributed implementation of the collapse compression technique used by explicit state model checkers to reduce memory usage. This adapatation makes use of lock-free distributed hash tables based on one-sided communication primitives provided by libraries such as OpenSHMEM. We implemented this technique in the distributed version of the model checker Helena. We report on experiments performed on the Grid'5000 cluster with an implementation over OpenMPI. These reveal that, for some models, this distributed implementation can altogether preserve the memory reduction provided by collapse compression and reduce execution times by allowing the exchanges of compressed states between processes.
LOVE 27/02/2019 On importance splitting and the automation of rare event simulation, par Carlos E. Budde
Carlos E. Budde, University of Twente  
Salle A303, bâtiment A, Université de Villetaneuse
27/02/2019    15:22 - 13:30
Résumé :
In the analysis of formal models, simulation based approaches like statistical model checking offer a solution to the state space explosion that hinders verification, but may suffer from long execution times. This is exacerbated when the property value to approximate depends on an event seldom observed; in those cases rare event simulation (RES) techniques can speed up convergence by reducing the variance of the statistical estimator. However, RES techniques typically require non-trivial and domain-specific (or even model-specific) user input, which is a setback w.r.t. the push-button approach of standard model checking. In this talk I will briefly discuss methods to automate the implementation of a specific approach to RES called "importance splitting." I will overview some known implementations and discuss two algorithms recently developed to select "importance thresholds" and "splitting/effort factors," which are parameters with direct impact on the efficiency of importance splitting. A good performance of the outcomes of the algorithms proposed has been empirically demonstrated on several case studies.
LOVE 27/02/2019 Towards parallel verification of concurrent systems, par Hiba OUNI
Hiba OUNI  
Salle A303, bâtiment A, Université de Villetaneuse
27/02/2019    15:22 - 13:30
Résumé :
An efficient way to cope with the combinatorial explosion problem induced by the model checking process is to compute the Symbolic Observation Graph (SOG). The SOG is defined as a condensed representation of the state space based on a symbolic encoding of the nodes (sets of states). It has the advantage to be much reduced comparing to the original state space graph while being equivalent with respect to linear time properties. Aiming to go further in the process of tackling the state space explosion problem, we propose to parallelize the construction of the SOG using three different approaches. A multi-threaded approach based on a dynamic load balancing and a shared memory architecture, a distributed approach based on a distributed memory architecture and a hybrid (shared-distributed memory) approach that combines the two previous app roaches. We implement these algorithms, we study their performances and we compare them to each other and to the sequential construction of the SOG. Experiments show that parallel approaches can improve drastically the performances of the SOG computation regarding a sequential construction. Afterwards, we go a step forward in improving the SOG construction process by reducing, on the fly, the size of the graph. We provide a symbolic (LDD-based) dichotomy-based algorithm to canonically reduce the size of the SOG aggregates. We implement this algorithm within the three parallel approaches. We conduct experiments in order to measure the impact of the canonization on the SOG construction. Results show that the canonization allows to efficiently decrease memory consumption in all approaches. Also, it allows to improve the scalability for both distributed and hybrid approaches.
LOVE 27/02/2019 Linear Implicative Algebras, a Brouwer-Heyting-Kolmogorov interpretation of linear logic, par Luc Pellissier
Luc Pellissier, IRIF  
Salle B107, bâtiment B, Université de Villetaneuse
27/02/2019    15:22 - 12:00
Résumé :
Implicative Algebras were recently introduced by Alexandre Miquel as a unified framework for forcing and realisability, whose particularity is to interpret terms and formulæ uniformly. In this ongoing work, we show how linear logic fits in this picture: we present a notion of model of intuitionnistic linear logic in which sits both syntactic models and a localized phase semantics ; and show how to transform such a model into an algebra allowing to interpret faithfully all the connectives of classical linear logic.
AOC 12/02/2019 Méthodes pour la résolution de très grands problèmes combinatoires stochastiques. Application à un problème industriel d'EDF., par Rodolphe Griset
Rodolphe Griset, EDF  
Salle B107, bâtiment B, Université de Villetaneuse
12/02/2019    12:15 - 13:15
Résumé :
Cette exposé s'intéresse à la résolution de très grands problèmes d'optimisation combinatoire stochastique. Les recherches sont appliquées au problème de planification des arrêts pour rechargement des centrales nucléaires. Compte-tenu de la part prépondérante de celles-ci dans le mix-électrique, ce problème structure fortement la chaîne de management d’énergie d'EDF. Une première partie propose une formulation étendue à deux niveaux dans laquelle les décisions de premier niveau fixent les plannings d’arrêt et des profils de production des centrales, et celles de second niveau évaluent le coût de satisfaction de la demande associé. Cette formulation permet la résolution à l'optimum d'instances industrielles déterministes par un solveur en PLNE. Dans le cas stochastique, une telle résolution directe du problème n'est plus possible. Nous proposons une formulation permettant d’en résoudre la relaxation linéaire par génération de colonnes et de coupes, correspondant respectivement aux reformulations de Danzig-Wolfe du premier niveau et de Benders du second. Une phase heuristique permet ensuite de déterminer des solutions entières de bonne qualité pour des instances, jusqu'à une cinquantaine de scénarios représentatifs de l’incertitude sur les données. L’apport de l’approche est estimé en utilisant les outils industriels exploités par EDF pour évaluer les plannings. Une seconde partie porte sur l'intégration de méthodes d'optimisation robuste pour la prise en compte d’aléas sur la disponibilité des centrales. Nous nous plaçons dans un cadre où les recours possibles sur les dates d'arrêts ne sont pas exercés. Nous comparons des méthodes bi-objectif et probabiliste permettant de rendre le planning robuste pour les contraintes opérationnelles dont la relaxation est envisageable. Pour les autres, nous proposons une méthode basée sur un budget d’incertitude. Cette méthode permet de renforcer la stabilité du planning en limitant les besoins de réorganisation futurs. La prise en compte d’une loi de probabilité de l’aléa permet d’affiner le contrôle du prix de cette robustesse.
RCLN 11/02/2019 Review of neural automatic summarization of conversations for a medical chatbot, par Jessica Lopez Espejel
Jessica Lopez Espejel, CEA  
Salle B107, bâtiment B, Université de Villetaneuse
11/02/2019    14:00 - 16:00
Résumé :
Conversation analysis plays an important role in the development of simulation devices for training health professionals (doctors, nurses). The goal of the thesis is to develop an original automatic summarization method for medical conversations between a patient and a health professional based on recent convolutional and recurrent neural summarization advances. The proposed method should be adapted to the specific problems of summarizing dialogues (and trained with abundant data from medical conversations between doctor and patients). The hypothesis is that pertinent blocks of dialogue might be extracted by tagging medical topics to dialog blocks and detecting topic evolution through deep learning.
A3 07/02/2019 Stochastic Majorize-Minimize Subspace Algorithm for Large Scale Data Processing, par Emilie Chouzenoux
Emilie Chouzenoux, Université de Marne la Vallée, INRIA  
Salle B107, bâtiment B, Université de Villetaneuse
07/02/2019    12:15 - 13:45
Résumé :
Stochastic approximation techniques play a prominent role in solving many large scale problems encountered in machine learning or image/signal processing. In these contexts, the statistics of the data are often unknown a priori or their direct computation is too intensive, and they have thus to be estimated online from the observations. For batch optimization of an objective function being the sum of a data fidelity term and a penalization (e.g. a sparsity promoting function), Majorize-Minimize (MM) methods have recently attracted much interest since they are fast, highly flexible, and effective in ensuring convergence. The goal of this talk is to show how these methods can be successfully extended to the case when the data fidelity term corresponds to a least squares criterion and the cost function is replaced by a sequence of stochastic approximations of it. In this context, we propose an online version of an MM subspace algorithm and we establish its convergence by using suitable probabilistic tools. We also provide new results on the convergence rate of such kind of algorithm. Numerical results illustrate the good practical performance of the proposed algorithm associated with a memory gradient subspace, when applied to both non-adaptive and adaptive linear system identification scenarios.
A3 31/01/2019 Approches génériques pour le traitement des données textuelles et numériques volumineuses, changeantes et multi-vues et des données en graphes, par Jean-Charles Lamirel
Jean-Charles Lamirel, LORIA, Nancy  
Salle B107, bâtiment B, Université de Villetaneuse
31/01/2019    12:15 - 13:45
Résumé :
Face à la croissance continue des informations numériques, de multiples natures, qui sont disponibles en ligne, un des challenges importants pour les linguistes et les analystes de l'information, afin de pouvoir formuler des hypothèses et de valider des modèles, est d'exploiter des outils efficaces pour l'analyse de données, capables de s'adapter à des volumes importants de données hétérogènes, changeantes et souvent et de nature distribuée et multi-vues. Nous aborderons dans cette présentation les principes généraux de la maximisation des traits, une nouvelle approche statistique générique initialement dédiée au traitement des données textuelles volumineuses, mais généralisable à tout type de données numériques dynamiques et multi-vues ou à des données hybrides (textuelles-numériques) et à des données en graphe. Nous reviendrons sur ses différentes applications à succès dans les deux cadres, supervisé et non supervisé, en comparant ses performances avec celles des méthodes de l’état de l’art sur des corpus de données de référence. Nous montrerons les avantages supplémentaires liés à son intégration dans un paradigme d’analyse multi-vues basé sur le raisonnement bayésien non supervisé. Nous mettrons finalement en évidence l’intérêt de cette méthode pour l’extraction d’information dans les grands graphes et pour la comparaison de graphes de taille et de densité variable.
A3 17/01/2019 Characterizing community detection algorithms and detected modules in large-scale complex networks, par Vinh Loc DAO
Vinh Loc DAO, IMT Atlantique  
Salle B107, bâtiment B, Université de Villetaneuse
17/01/2019    12:15 - 13:45
Résumé :
La détection de communauté est une technique qui décompose des graphes en sous-graphes densément connectés, ce qui est particulièrement utile dans le cas de (très) grands réseaux complexes dont la visualisation est difficile. De très nombreuses méthodes, très variées ont été proposées ces dernières années. Dans un contexte où aucun consensus n'émerge autour de la notion même de communauté, ces méthodes provoquent de multiples discussions scientifiques autour de la qualité de leur résultat. Dans cette thèse, nous proposons plusieurs types d'évaluation comparative et approfondie de 16 méthodes bien connues de l'état de l'art ainsi que la caractérisation exhaustive des structures communautaires découvertes dans des réseaux réels variés provenant de domaines différents. Nos résultats - méthodes et analyses - constituent un début de boîte à outils pour l'analyste bien en peine de choisir la méthode adaptée à son étude.
AOC 18/12/2018 Integer Programming approaches for Vertex Coloring Problems and for some applied projects, par Diego Delle Donne
Diego Delle Donne, Seminaire  
Salle B107, bâtiment B, Université de Villetaneuse
18/12/2018    12:15 - 13:30
Résumé :
This seminar presents several variants of the classical vertex coloring problem together with an overview on some theoretical and practical results related to Integer Programming approaches for these problems. The practical aspect involves implementations of competitive algorithms for these problems while the theoretical aspect relates to polyhedral studies of some formulations with the goal of finding "nice" characterizations for the associ ated polytopes.
RCLN 05/11/2018 Learning to Navigate and Extract Information from Web Results, par Ivan Vladimir MEZA
Ivan Vladimir MEZA, UNAM Mexique  
Salle B107, bâtiment B, Université de Villetaneuse
05/11/2018    14:00 - 15:00
Résumé :
In this talk I present our progress into the ECOS-NORD project between LIPN-Paris 13 and IIMAS-UNAM at Mexico. The talk focus on our experimental setup that allows to learn to navigate web results and to extract information from them. In particular, at this stage we are focus on extracting biográfical information of researchers, in order to quantify the Mexican returning diaspora. Our experimental setup is based on a reinforcement learning setup, we use a labelled data to learn the main actions on the results grid. We will show preliminary results, and newlines of experimentation.
A3 25/10/2018 Apprentissage automatique et adaptatif pour le clustering de flux de données relationnelles, par Parisa Rastin
Parisa Rastin, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
25/10/2018    12:15 - 13:45
Résumé :
Les approches basées sur les prototypes sont très populaires en apprentissage non supervisé, en raison de la compacité du modèle résultant (les prototypes), de la puissance descriptive de ces prototypes et de la faible complexité de calcul du modèle (chaque objet est comparé à un petit nombre de prototypes). Nous proposons une approche de K-moyennes relationnelle utilisant un ensemble unique de points de support à travers le processus d'apprentissage, puis on introduit le formalisme des Coordonnées Barycentriques afin d'unifier la représentation des objets et des prototypes, ce qui permet un processus d'apprentissage incrémental simple pour le clustering relationnel. Notre motivation pratique est de réaliser un profilage en temps réel des utilisateurs connectés. Les tâches de profilage visent à reconnaître "l'état d'esprit" des utilisateurs à travers leur navigation sur différents sites en ligne.
MERCRED 03/10/2018 First Order Algorithms for Constrained Optimization Problems in Machine Learning, par Francesco Rinaldi
Francesco Rinaldi, Université de Padoue  
Salle B107, bâtiment B, Université de Villetaneuse
03/10/2018    14:00 - 15:00
Résumé :
Thanks to the advent of the "Big Data era", simple iterative first-order optimization approaches for constrained convex optimization have re-gained popularity in the last few years. In the talk, we first review a few classic methods (i.e., conditional and projected gradient method) in the context of Big Data applications. Then, we discuss both theoretical and computational aspects of some new active-set variants for those classic methods. Finally, we examine current challenges and future research perspectives. DISCLAIMER: This aimes to be a wide audience talk (for any LIPN member, Ph. D. students included) and you are not assume to know what is a "first-order optimization approach", a "conditional or projected gradient method" or an "active-set variant".
AOC 25/09/2018 Modèles d'optimisation pour le transport urbain "flexible", par Yasmin A. Rios-Solis
Yasmin A. Rios-Solis, Universidad Autónoma de Nuevo León  
Salle B107, bâtiment B, Université de Villetaneuse
25/09/2018    12:30 - 13:30
Résumé :
Je présenterai des problèmes de transport urbain (bus) qui se trouvent dans un contexte “flexible” ou plutôt, “désordonné”: chauffeurs absents, événements inattendus qui arrivent aux véhicules, pas de voie spéciale pour les bus, presque pas d’arrêts et compétition entre compagnies de transport. Pour ces problèmes, il faut de nouveau modèles d’optimisation, des preuves de complexité et de nouvelles méthodes de résolution. Au lieu de rentrer dans les détails mathématiques, je présenterai plutôt les thèmes de recherche qui émergent de ce contexte flexible.
RCLN 03/09/2018 Analysing large-scale Research Data with Semantic Technologies, par Francesco OSBORNE
Francesco OSBORNE, Knowledge Media Institute, Open University (UK)  
Salle B107, bâtiment B, Université de Villetaneuse
03/09/2018    16:00 - 17:30
Résumé :
Semantic Technologies provide useful solutions for the analysis of big scholarly data since they facilitate the integration of large datasets and support tasks such as Natural Language Processing and Information Retrieval. In particular, ontologies that describe research topics and their relationships proved to be effective tools for making sense of research dynamics, classifying publications, detecting research communities, and forecasting research trends. However, these knowledge bases are very expensive to craft and tend to become obsolete fairly quickly. In my talk, I will discuss the automatic approach that we designed to generate and update the Computer Science Ontology (CSO), a large-scale ontology of research topics including about 25K concepts. CSO has been used for supporting Springer Nature in classifying editorial products, informing marketing decisions, and evolving their internal taxonomy. I will present some systems adopting this knowledge base and describe their effect on the workflow of a major publishing company. I will also discuss the advantage of combining Machine Learning and Semantic Technologies for addressing complex tasks such as predicting research trends and forecasting technology migrations.
A3 05/07/2018 Towards more Autonomous Robots, par Eduardo Morales
Eduardo Morales, INAOE, Mexico  
Amphi Copernic, Institut Galilée, Université de Villetaneuse
05/07/2018    12:15 - 13:45
Résumé :
With the increasing incorporation of robots into daily life activities, autonomy and interaction with non expert users play a central role in robotics research. In this talk, I will describe two developments towards this aim. First I will describe how a robot can autonomously extract information from Internet to decide where to find an unknown object and how to learn on-line a recognition model. In the second part of the talk I will describe how a non-expert user can train a robot to perform simple tasks combining programming by demonstration, reinforcement learning and user's feedback.
MERCRED 04/07/2018 Cost Efficient Prediction of Wine Quality - A Machine Learning Approach, par Razvan Andonie
Razvan Andonie, Central Washington University  
Salle B107, bâtiment B, Université de Villetaneuse
04/07/2018    14:00 - 15:00
Résumé :
The quality of wines can be assessed both from chemical/biological tests and sensory tests (which rely mainly on human experts). Determining which is the subset of tests to be used is a difficult problem. Each test has its own contribution for predicting the quality of wines and, in addition, its own cost. We use our own database, consisting of 32 wine characteristics applied to 180 wine samples. In addition we use wine quality labels assigned by a wine expert. To the extent of our knowledge, this is the first study of this kind on wines from Washington State, and also the first wine study in general to include cost minimization of the measurements as a goal. Our approach is based on two stages. First, we identify reasonably good classifiers (from a given set of classifiers). Next, we search for the optimal subset of features to maximize the performance of the best classifier and also minimize the overall cost of the measurements. As a result, through our method we can answer queries like ``the best performing subset of tests for a given threshold costÂ’'.
RCLN 02/07/2018 Multi-Arabic Dialect Applications and Resources, par Nizar Habash
Nizar Habash, NYU Abu Dhabi  
Salle B107, bâtiment B, Université de Villetaneuse
02/07/2018    14:00 - 15:00
Résumé :
We present the Multi-Arabic Dialect Applications and Resources (MADAR) Project. MADAR is an effort to build parallel resources for 25 Arab city dialects including lexicons, parallel corpora, and orthographic and morphological annotation guidelines. The created resources have been used to develop dialect identification and machine translation applications. We discuss the challenges facing Arabic dialect modeling, as well as our solutions and results.
A3 28/06/2018 Hyperparameter Optimization for Neural Networks, par Razvan Andonie
Razvan Andonie, Central Washington University, USA  
Salle B107, bâtiment B, Université de Villetaneuse
28/06/2018    14:00 - 15:30
Résumé :
We introduce a dynamic early stopping condition for Random Search optimization algorithms. We test our algorithm for SVM hyperparameter optimization for classification tasks, on six commonly used datasets. According to the experimental results, we reduce significantly the number of trials used. Since each trial requires a re-training of the SVM model, our method accelerates the RS optimization. The code runs on a multi-core system and we analyze the achieved scalability for an increasing number of cores.
MERCRED 27/06/2018 Research Efforts at the Computational Approaches to Modeling Language Lab., par Nizar Habash
Nizar Habash, NYU Abu Dhabi, Saadiyat Island  
Salle Darwin, institut galilée
27/06/2018    14:00 - 15:00
Résumé :
TBA
RCLN 25/06/2018 The Arabic Ontology and Modernization of Lexical Semantic Resources, par Mustafa Jarrar
Mustafa Jarrar, Computer Science Department, Birzeit University, Palestine  
Salle B107, bâtiment B, Université de Villetaneuse
25/06/2018    14:00 - 15:00
Résumé :
The importance of lexical-semantic resources (linguistic ontologies, wordnets, thesauri, and dictionaries) is increasing in many modern application scenarios, such as multilingual big data, data governance, information retrieval, NLP, social networks, and others. In this talk we will present our experience in digitizing 150 multilingual lexicons and present the Arabic Ontology, which is a formal Arabic Wordnet with ontologically-clean content. We will also discuss how this content is ontologically we ll-founded and benchmarked to scientific advances rather than to speakersÂ’ nai?ve beliefs as wordnets typically do, in addition to top levels and other ontology engineering challenges and mappings to other ontologies.
A3 21/06/2018 Proposition et consommation de contenus sur le web : le problème de la diversité., par Lionel Tabourier
Lionel Tabourier, Complex Networks, LIP6  
Salle B107, bâtiment B, Université de Villetaneuse
21/06/2018    12:15 - 13:45
Résumé :
La question de la diversité des contenus proposés et consommés sur le web apparaît tôt dans la littérature de recherche d'information. Pourtant, ce n'est que récemment que celle-ci a évolué vers un débat de société, parce qu'un nombre croissant d'utilisateurs des moteurs de recherche ou des plateformes de recommandation sont confontés à leurs effets secondaires néfastes. Un des plus notables est l'enfermement dans des bulles d'information, c'est-à-dire l'exposition à des contenus de moins en moins divers, correspondant à un environnement culturel restreint. L'objet du projet ANR Algodiv (http://algodiv.huma-num.fr/) est d'étudier comment le concept de diversité est traduit et mis en oeuvre par les algorithmes du web. Dans cet exposé, je présenterai deux aspects de cette question, qui sont des chantiers de travail actifs du projet. D'abord, nous examinons l'effet des algorithmes de recommandation sur la diversité proposée aux utilisateurs. Moyennant une définition adéquate de la notion de diversité sur une plateforme de recommandation, nous cherchons à "auditer" les archétypes de recommandation, c'est-à-dire à mesurer la tendance d'une méthode à enfermer l'utilisateur à plus ou moins long terme. D'autre part, nous étudions les caractéristiques des pratiques de navigation des utilisateurs sur l'exemple de la navigation sur le site Melty (https://www.melty.fr/). Nous examinons à quel point ceux-ci tendent à consommer des contenus variés ou non en fonction de ce qui leur est proposé, de la période, du moyen d'accéder à l'information, etc.
A3 14/06/2018 Deep Cooperative Reconstruction with Privacy Constraints, par Denis Maurel
Denis Maurel, ISEP, équipe RDI  
Salle B107, bâtiment B, Université de Villetaneuse
14/06/2018    12:15 - 13:45
Résumé :
Nowadays, we can observe a multiplication of multi-view data in domains such as marketing, bank administration or even survey analysis. In this context, Machine Learning methods are used to analyze data from several heterogeneous sources (here called views) with the following problem: an individual described in some views might be missing in some other ones. This proliferation is accompanied by a global privacy awareness: one should never have access to data from all sources at once. To solve these problems, we propose a method called the Cooperative Reconstruction System (CRS) which aims at reconstructing missing individuals locally using information contained in external views without data transfer from a view to another.
MERCRED 13/06/2018 Network Interdiction, par Joe Naoum-Sawaya
Joe Naoum-Sawaya, Ivey Business School, London, ON, Canada  
TBA (Institut Galilée)
13/06/2018    14:00 - 15:00
Résumé :
Network interdiction is a class of leader-follower optimization problem that seeks to identify network components to disrupt and inflict a maximum damage to a network. The objective of such models is to study the structural connectivity of the network in order to identify vulnerabilities. The application areas are diverse and include energy, telecommunication, and supply chain networks among others. This talk will review two particular variations of network interdiction: connectivity disruption and flow disruption. The connectivity disruption model identifies the nodes in a network whose disruption minimizes the maximum number of connected node pairs. The flow disruption model identifies the edges whose disruption minimizes the maximum flow between sources and destinations. We will present optimization models as well as solution approaches. We will particularly focus on the cases where uncertainty is present in the edge weights and propose customized solution approaches based on robust optimization, cutting planes, and Benders decomposition. The proposed cutting planes and Benders decomposition exploit the structure of the underlying optimization model and allows the modeling and the solution of general classes of uncertainty sets.
CALIN 05/06/2018 Théorie de la complexité et géométrie des orbites du déterminant et du permanent, par Christophe Tollu
Christophe Tollu, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
05/06/2018    10:30 - 12:15
Résumé :
Après un rappel sur les circuits arithmétiques et le problème de Valiant (VP vs VNP), je présenterai quelques résultats récents sur la "complexité déterminantale" du permanent, puis montrerai comment la version purement algébrique du problème VP vs VNP se prête à une reformulation en termes de géométrie des orbites du déterminant et du permanent (pour l'action d'un groupe algébrique sur les polynômes homogènes). Plusieurs ingrédients de base du programme de théorie géométrique de la complexité de Mulmuley et Sohoni seront présentés au cours de l'exposé bien que celui-ci ne soit pas "A crash course on Geometric Complexity Theory".
A3 31/05/2018 Graphes dynamiques - Modélisation et Clustering, par Tabea Rebafka
Tabea Rebafka, LIP6, UPMC  
Salle B107, bâtiment B, Université de Villetaneuse
31/05/2018    12:15 - 13:45
Résumé :
To model recurrent interaction events we propose a new dynamic random graph model : an extension of the stochastic block model in continuous time, where every individual (node) belongs to a latent group and interactions (edges) between two individuals are modelled using inhomogeneous Poisson processes. We develop a semiparametric variational expectation-maximization algorithm to estimate model parameters and to perform a clustering of the nodes. We illustrate the performance of our method on real datasets.
CALIN 29/05/2018 Combinatorics of chemical reaction systems, par Nicolas Behr
Nicolas Behr, IRIF Paris VII, Endinburgh University  
Salle B107, bâtiment B, Université de Villetaneuse
29/05/2018    14:00 - 16:00
Résumé :
Reporting on recent work with G.H.E. Duchamp and K.A. Penson (arXiv:1712.06575), I plan to present a formulation of chemical reaction systems in the so-called stochastic mechanics formalism. This approach allows to uncover some deep relationships between the combinatorial techniques of boson normal-ordering and the dynamics of chemical reaction networks: each semi-linear reaction type induces an evolution within a space of probability distributions that can be computed explicitly via our techniques. For the interesting remaining types of reactions, some results involving systems of Sobolev-Jacobi orthogonal polynomials will be presented.
CALIN 29/05/2018 (CIP) Discussion on graph rewriting systems (with examples and equations), par Nicolas Behr
Nicolas Behr, IRIF Paris VII, Endinburgh University  
Salle B107, bâtiment B, Université de Villetaneuse
29/05/2018    11:00 - 12:15
Résumé :
Séminaire annulé à cause de difficultés de transport. Le séminaire de 14h00 est maintenu.
MERCRED 23/05/2018 A New Branch-and-Price-and-Cut Algorithm for One-Dimensional Bin Packing Problems, par Roberto Baldacci
Roberto Baldacci, Bologne  
Salle B107, bâtiment B, Université de Villetaneuse
23/05/2018    15:00 - 16:00
Résumé :
In this work, a new branch-and-price-and-cut algorithm is proposed to solve the one-dimensional bin packing problem (1D-BPP). The 1D-BPP is one of the most fundamental problems in combinatorial optimization and has been extensively studied for decades. Recently, Delorme et al. (2016) proposed 500 new test instances for the 1D-BPP; the best exact algorithm proposed in the literature can optimally solve 167 of these new instances, with a time limit of one hour imposed to each execution of the algorithm. The exact algorithm proposed in this paper is based on the classical set-partitioning model for the 1D-BPP and the subset-row inequalities proposed by Jepsen et al. (2008). We describe an ad-hoc label-setting algorithm to solve the pricing problem, dominance and fathoming rules to speedup its computation and a new primal heuristic. The exact algorithm can easily handle some practical constraints, like the incompatibility between the items, and therefore we also apply it to solve the 1D-BPP with conflicts (1D-BPPC). The proposed method is tested on a large family of 1D-BPP and 1D-BPPC classes of instances. For the 1D-BPP, the proposed method can optimally solve 237 instances of the new set of difficult instances; the largest instance involves 1003 items and bins of capacity 80,000. For the 1D-BPPC, the experiments show that the method is highly competitive with state-of-the-art methods, and successfully closed several open 1D-BPPC instances.
MERCRED 23/05/2018 Facteurs premiers de nombres remarquables, par Florian Luca
Florian Luca, Johannesburg  
Salle B107, bâtiment B, Université de Villetaneuse
23/05/2018    14:00 - 15:00
Résumé :
Soit une suite de nombres entiers et considérons le produit des n premiers termes. Combien ce produit a-t-il de facteurs premiers ? Quel est le plus grand ? Nous présenterons différents résultats concernant des suites célèbres : les nombres de Fermat, de Fibonacci, ...
CALIN 15/05/2018 Hom-idempotent graphs, normal Cayley graphs and stable Kneser graphs, par Mario Valencia Pabon
Mario Valencia Pabon, LIPN, Univ. Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
15/05/2018    14:00 - 15:00
Résumé :
Dans cet exposé, on parlera de la notion de hom-idempotence dans l'ensemble de graphes : un graphe G est dit hom-idempotent s'il existe un homomorphisme entre le graphe produit cartésien G*G et G lui-même. Cette notion est fortement liée à une classe particulière de graphes de Cayley qu'on appelle les graphes de Cayley normaux. On montrera que les graphes de Kneser K(n,k) ne sont pas hom-idempotents. On montrera aussi que les graphes s-stables de Kneser K(n,k)_s ne sont pas hom-idempotents si s=2 mais, pour n=sk+1, K(n,k)_s est hom-idempotent. Finalement, on appliquera la notion de hom-idempotence à la k-tuple coloration de graphes : une k-tuple coloration de graphes consiste en affecter à chaque sommet un k-ensemble de couleurs de sorte que sommets adjacents reçoivent k-ensembles disjoints. On montrera que la différence entre le nombre chromatique du graphe produit cartésien de graphes de Kneser K(n,k)*K(n,k) et le nombre chromatique d'une 2-tuple coloration du même graphe K(n,k)*K(n,k) n'est pas bornée.
AOC 15/05/2018 Strong and Cheap SDP and SOCP Hierarchies for Polynomi al Optimization, par Bissan Ghaddar
Bissan Ghaddar, University of Waterloo  
Salle B107, bâtiment B, Université de Villetaneuse
15/05/2018    12:30 - 13:30
Résumé :
In this talk, we propose alternative SDP and SOCP approximation hierarchies to obtain global bounds for general polynomial optimization problems (POP), by using SOS, and SDSOS polynomials to strengthen existing hierarchies for POPs. Specifically, we show that the resulting approximations are substantially more effective in finding solutions of certain POPs for which the more common hierarchies of SDP relaxations are known to perform poorly. Numerical results based on the proposed hierarchies are presented on non-convex instances form the literature as well as on instances from the GLOBAL Library.
CALIN 15/05/2018 Phylogenetic trees modeled by increasing Schröder trees, par Mehdi Naima
Mehdi Naima, LIPN (Doctorant Équipe CALIN, dir : Olivier Bodini)  
Salle B107, bâtiment B, Université de Villetaneuse
15/05/2018    11:00 - 12:00
Résumé :
In biology a phylogenetic tree is a classical tool to represent the evolutionary relationship among species. Our main frustration against the classical combinatorial models is related to the chrono- logical aspect that seems not considered by the models. E. g. the Schröder trees do not take into account the time evolution. We develop in this paper a model for phylogenetic trees satisfying in priority two constraints: (1) to take into account the chronological evolution and (2) to be efficient to simulate. Our model is based on some increasingly labeling of Schröder trees.
MERCRED 02/05/2018 Discrete convexity and applications to combinatorics and optimization, par Gleb Koshevoy
Gleb Koshevoy, Central Institute of Economics & Mathematics  
Salle B107, bâtiment B, Université de Villetaneuse
02/05/2018    14:00 - 15:00
Résumé :
I will explain theory convexity for lattices, free Abelian groups without torsion. I will show that a famous class of polytopes, polymatroids of combinatorial optimization, is related to one of classes of discrete convexity. Several instances of discretely convex functions related to combinatorics of Young tableaux will be demonstrated.
CALIN 24/04/2018 Facteurs cyclotomiques des polynômes de Serre, par Florian Luca
Florian Luca, University of the Witwatersrand  
Salle B107, bâtiment B, Université de Villetaneuse
24/04/2018    14:00 - 15:00
Document attaché
Résumé :
https://lipn.fr/~cb/Seminaires/resume.php?L=1165
CALIN 24/04/2018 CIP : Théorie de Picard-Vessiot et équations différentielles non commutatives, par Hoang Ngoc Minh
Hoang Ngoc Minh, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
24/04/2018    11:00 - 12:30
Résumé :
Attention : Horaire décalé à 11h00 vu les difficultés de transport.
MERCRED 18/04/2018 Apprentissage et génération de représentations optimisées de données complexes, par Abdelkader Benyettou
Abdelkader Benyettou, Université d'Oran, Algérie  
Salle B107, bâtiment B, Université de Villetaneuse
18/04/2018    14:00 - 15:00
Résumé :
On propose une approche mimétique pour l’apprentissage et la génération de représentations optimisées de données complexes à travers la sélection et la pondération simultanée des attributs basée sur une hybridation entre une approche évolutionnaire et l’apprentissage sous contraintes des machines à vecteurs de support. Cette technique a été expérimentée sur l’optimisation de la classification des documents web ainsi que des images aériennes. Cependant, les représentations usuelles des données complexes engendrent des matrices de très grandes dimensionnalités dont le traitement par une approche mimétique peut s’avérer très lourd en temps de calcul lors de la phase d’apprentissage. On propose une implémentation parallèle de l’algorithme proposé basée sur les modèles d’îlots afin de palier à ce problème. Nos expériences sur plusieurs benchmarks : Reuters- 21578, 7Sectors, Webkb et UCMerced LandUse ont montré qu’on peut réduire significativement le temps d’exécution ainsi que le nombre d’attributs avec une nette amélioration des performances en classification.
A3 05/04/2018 Apports de la Programmation Linéaire en Nombres Entiers pour la modélisation et l'extraction d'ensembles de motifs, par Abdelkader Ouali
Abdelkader Ouali, Équipe Modèles, Agents et Décision, laboratoire GREYC, université de Caen Normandie.  
Salle B107, bâtiment B, Université de Villetaneuse
05/04/2018    12:15 - 13:45
Résumé :
Un problème récurrent en extraction de motifs est la sélection de motifs pertinents parmi le grand ensemble de motifs découverts. Pour réduire le nombre de motifs extraits et donc de faciliter l'analyse du résultat de la fouille est l'extraction de motifs de plus haut niveau reposant sur des caractéristiques qui impliquent plusieurs motifs locaux. Ces motifs sont appelés ensembles de motifs ou pattern sets. Extraire le meilleur ensemble de motifs relativement à une mesure donnée permet de mieux cibler le processus d’extraction vers les meilleurs motifs mais rend la tâche plus ardue, notamment en raison de la taille importante de l'espace de recherche et le manque de techniques d'élagage efficaces pour ce type de problèmes. La plupart des approches existantes (souvent heuristiques) sacrifient la preuve d'optimalité au détriment de solutions approchées. Toutefois, la qualité de solutions obtenues par ces approches reste très variable. La PLNE (Programmation Linéaire en Nombres Entiers) est un au cadre générique qui procure un haut niveau de flexibilité et d’expressivité pour composer différentes types de contraintes. L'utilisation de la PLNE pour la modélisation de tâches d’optimisation en fouille de données est un domaine qui a été très peu exploré. C'est dans ce cadre que s'inscrivaient mes travaux de thèse. Dans cet exposé, je vais montrer comment la PLNE peut être utilisée pour modéliser différentes contraintes portant sur des ensembles de motifs. Outre le cadre général de l’extraction d'ensembles de motifs, je vais illustrer l’intérêt de mon approche sur deux problèmes bien connus en fouille de données : le clustering conceptuel et le problème de pavage (tiling). Enfin, je présenterai quelques résultats récents sur l'utilisation des moyennes ordonnées pondérées (communément appelées OWA pour Ordered Weighted) afin de trouver un équilibre optimal sur la taille des clusters du clustering conceptuel.
CALIN 27/03/2018 Cluster relations among Schur functions and a positivity conjecture, par Gleb Koshevoy
Gleb Koshevoy, Moscou (Poncelet Center CNRS UMI 2615)  
Salle B107, bâtiment B, Université de Villetaneuse
27/03/2018    14:00 - 15:30
Résumé :
Cluster algebras, invented by Sergey Fomin and Andrei Zelevinsky around 2000, are commutative algebras whose generators and relations are constructed in a recursive manner. Due to cluster recursion we obtain Laurent polynomials in the initial variables, so-called Laurent phenomenon of cluster algebras. The coordinate ring of base affine space C[N_-\SL_n] plays an important role in representation theory and is endowed with a cluster algebra structure. We show that under specialization of minors to Schur functions, Laurent polynomials of this cluster algebra turn into 'homogeneous' sums of Schur function. A positivity conjecture says that these sums have positive coefficients. This conjecture is true for finite cluster subalgebras.
AOC 27/03/2018 Complexity of the cluster deletion problem on cographs and subclasses of chordal graphs , par Mario Valencia Pabon
Mario Valencia Pabon, Paris 13  
Salle B107, bâtiment B, Université de Villetaneuse
27/03/2018    12:30 - 13:30
Résumé :
We consider the following vertex-partition problem on graphs, known as the CLUSTER DELETION (CD) problem: given a graph with real nonnegative edge weights, partition the vertices into clusters (in this case, cliques) to minimize the total weight of edges outside the clusters. The decision version of this optimization problem is known to be NP-complete even for unweighted graphs and has been studied extensively. In this talk, I will focus on the complexity of the decision CD problem for the family of chordal graphs, showing that it is NP-complete for weighted split graphs, weighted interval graphs and unweighted chordal graphs. We will also see that the problem is NP-complete for weighted cographs. Some polynomial-time solvable cases of the optimization problem will be identified, in particular CD for unweighted cographs, split graphs, unweighted proper interval graphs and weighted block graphs. This is a joint work with Flavia Bonomo and Guillermo Duràn (University of Buenos Aires).
CALIN 27/03/2018 Combinatorial bases of KZn, par Gleb Koshevoy
Gleb Koshevoy, Moscou (Poncelet Center CNRS UMI 2615)  
Salle B107, bâtiment B, Université de Villetaneuse
27/03/2018    11:00 - 12:00
Résumé :
TBA (discussion)
CALIN 20/03/2018 On lattice polytopes, convex matroid optimization, and degree sequences of hypergraphs, par Antoine Deza
Antoine Deza  
Salle B107, bâtiment B, Université de Villetaneuse
20/03/2018    14:00 -
Résumé :
We introduce a family of polytopes, called primitive zonotopes, which can be seen as a generalization of the permutahedron of type Bd. We discuss connections to the largest diameter of lattice polytopes and to the computational complexity of multicriteria matroid optimization. Complexity results and open questions are also presented. In particular, we answer a question raised in 1986 by Colbourn, Kocay, and Stinson by showing that deciding whether a given sequence is the degree sequence of a 3-hypergraph is computationally prohibitive. Based on joint works with Asaf Levin (Technion), George Manoussakis (Paris Sud), Shmuel Onn (Technion).
AOC 20/03/2018 On the Interplay between Simple Mixed Integer Programs and Lot-Sizing, par Laurence A. Wolsey
Laurence A. Wolsey, CORE, Universit\'e catholique de Louvain  
Salle B107, bâtiment B, Université de Villetaneuse
20/03/2018    12:30 - 13:30
Document attaché
Résumé :
After introducing some of the most basic lot-sizing problems and their properties, we show how the study of tight MIP formulations for the convex hull of solutions of such problems has provided more general results for MIPs and vice versa. In particular we demonstrate the importance of compact extended formulations as well as the role of mixing sets, network dual MIPs and single node flow models.
CALIN 06/03/2018 Two fast parallel GCD algorithms of many integers, par Sidi Mohamed Sedjelmaci
Sidi Mohamed Sedjelmaci  
Salle B107, bâtiment B, Université de Villetaneuse
06/03/2018    14:00 -
Résumé :
On montre que le calcul du PGCD de ???? integers de ????(????) bits peut se faire en parallèle en temps ????(???? / log ????) avec ????(????????^(1+????) ) processors, pour tout 2 ? ???? ? ????^(3/2) / log ????, c'est-à-dire que le temps de calcul en parallèle ne dépend pas dépend du nombre d'entiers m considéré dans cet intervalle.
CALIN 20/02/2018 Disques browniens, par Jérémie Bettinelli
Jérémie Bettinelli  
Salle B107, bâtiment B, Université de Villetaneuse
20/02/2018    14:00 -
Résumé :
À l'instar du mouvement brownien qui apparaît comme limite d'échelle universelle de toute marche aléatoire raisonable, les disques browniens sont des espace métrique aléatoires qui apparaissent comme limite d'échelle universelle de modèles raisonables de cartes aléatoire du disque. Ces objets généralisent la carte brownienne de Miermont et Le Gall obtenue en considérent des cartes aléatoire de la sphère. Nous présenterons les disques browniens et en donneront quelques propriétés remarquables. Ce travail est en commun avec Grégory Miermont.
CALIN 30/01/2018 Aspects énumératifs et bijectifs des cartes combinatoires, par Wenjie Fang
Wenjie Fang  
Salle B107, bâtiment B, Université de Villetaneuse
30/01/2018    15:00 -
Résumé :
Les cartes combinatoires, étant un modèle riche, portent plusieurs aspects : algébrique, géométrique, bijective, ... Dans cet exposé, je présente un ensemble de résultats et de connexions dans le domaine de l'énumération des cartes, obtenus à travers des aspects différents. Nous verrons comment utiliser les outils algébrique, comme caractères du groupe symétrique et équations fonctionnelles, à énumérer les cartes. Nous verrons aussi comment étudier les autres objets dans la combinatoire, ici les intervalles du treillis de Tamari, à travers de l'aspect bijectif des cartes.
AOC 30/01/2018 Decomposition methods for quadratic programming, par Emiliano Traversi
Emiliano Traversi, AOC -LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
30/01/2018    12:30 - 13:30
Résumé :
The purpose of this talk is to present two decomposition methods for quadratic problems. First, we propose a methodological analysis on a family of reformulations combining Dantzig-Wolfe decomposition and Quadratic Convex Reformulation principles for binary quadratic problems. As a representative case study, we apply them to a cardinality constrained quadratic knapsack problem. Secondly, we analyze a simplicial decomposition like algorithmic framework that handles convex quadratic programs in an effective way. In particular, we propose two tailored strategies for solving the master problem and we describe a few techniques for speeding up the solution of the pricing problem. We report extensive numerical experiments on both real-world and generic quadratic programs.
RCLN 29/01/2018 Approches non supervisées pour l'extraction de relations sémantiques, par Kata Gabor
Kata Gabor, RCLN, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
29/01/2018    14:00 - 15:00
Résumé :
Les approches actuellement utilisées pour l’extraction d’informations et de connaissances s'appuient majoritairement à la classification supervisée ou semi-supervisée. Elles exploitent des bases de connaissances structurées qui fournissent un modèle des connaissances, et le plus souvent également des données annotées par des humains. Or, de telles ressources sont couteuses à produire en matière de temps et d’expertise, et l'adaptation de domaine pose des difficultés. Nous cherchons à mettre en oeuvre des méthodes d'extraction d'informations qui minimisent les besoins en intervention humaine. Nous proposons et comparons plusieurs approches à la tâche d'extraction non supervisée de relations sémantiques à partir de corpus. Les approches ont été évaluées sur un corpus de domaine de taille limité, ainsi que sur un corpus et un jeu d'évaluation de vocabulaire générique. La première approche utilise des word embeddings pour caractériser le sens des concepts et pour calculer la similarité relationnelle entre plusieurs paires de concepts. La deuxième approche utilise la fouille de motifs séquentiels, combiné avec l'analyse sémantique, pour identifier les contextes qui permettent de détecter les relations. Finalement, nous proposons des pistes d'amélioration, en particulier en ce qui concerne l'hybridisation des deux approches.
CALIN 16/01/2018 Chute de dimension pour les marches aléatoires sur les arbres aléatoires, par Pierre Rousselin
Pierre Rousselin  
Salle B107, bâtiment B, Université de Villetaneuse
16/01/2018    14:00 -
Résumé :
Nous nous intéressons à différents modèles d'arbres aléatoires et aux marches aléatoires sur les sommets de tels arbres. Dans le cas où la marche aléatoire est transiente, la marche part presque sûrement vers l'infini en empruntant un rayon aléatoire. La loi de ce rayon est appelée la mesure harmonique sur le bord de l'arbre. Un phénomène de chute de dimension se produit : cette mesure harmonique est presque sûrement concentrée sur une partie petite (au sens de la dimension de Hausdorff) du bord de l'arbre. Autrement dit, les trajectoires de la marche aléatoires sont presque sûrement comprises dans un sous-arbre beaucoup plus fin que l'arbre original. Cette théorie a été initiée par Russel Lyons, Robin Pemantle et Yuval Peres dans les années 1990. Plus récemment, Nicolas Curien, Jean-François Le Gall, puis Shen Lin ont étudié ce phénomène sur un autre modèle d'arbres aléatoires. Nous rappellerons leurs résultats et discuteront des généralisations (https://arxiv.org/abs/1708.06965 et https://arxiv.org/abs/1711.07920) sur lesquelles nous avons travaillé.
CALIN 19/12/2017 Phase transition for the hard-core model in the 2-dimensional lattice, par Juan Vera Lizcano
Juan Vera Lizcano  
Salle B107, bâtiment B, Université de Villetaneuse
19/12/2017    14:00 -
Résumé :
The hard-core gas model is a natural combinatorial problem that has played an important role in the design of new approximate counting algorithms and for understanding computational connections to statistical physics phase transitions. For a graph G = (V, E) and a fugacity t > 0, the hard-core model is defined on the set of independent sets of G where each independent set I has weight w(I) = |I|^t . The equilibrium state of the system is described by the Gibbs distribution in which each independent set I has probability ~ w(I). A long-standing open problem to establish the critical fugacity t* for the hard-core gas model on the 2-dimensional integer lattice Z^2. In particular, t* is the conjectured critical point for the phase transition between uniqueness of infinite-volume Gibbs measures on Z^2 when t < t* and non-uniqueness when t > t*. Empirical results identified the critical point t* ~ 3.79. The best known bounds show 2.538 < t* < 5.3646. In this talk the techniques to obtain these bounds will be discussed. Special emphasis will be given to the lower bound, which is based on connections between the decay of correlations on the lattice and on its self-avoiding walk tree.
AOC 19/12/2017 Characterization of the Flexibility of an Energy Consumer and Optimization of its Energy Usage, par Claude Le Pape
Claude Le Pape, Schneider Electric  
Salle B107, bâtiment B, Université de Villetaneuse
19/12/2017    12:30 - 13:30
Résumé :
The exploitation of flexibility in energy production and consumption is essential to avoid costly reinforcements of the power system and maintain security of supply while increasing the penetration of renewable (and intermittent) sources of energy. Let us focus on the "demand" side, i.e., on actors which are mostly consumers of energy: manufacturing plants, water networks, commercial buildings (or even elements in a building such as an HVAC (Heating, Ventilation and Air Conditioning) system, an elevator or a pool of elevators), and aggregations of those, such as a district. These actors use energy for their own needs, i.e., manufacture and deliver products to their own customers, deliver drinkable water to their customers, provide a comfortable work place to the employees and visitors of the building, etc. They may also produce energy, either as part of the process they manage (e.g., cogeneration in an industrial plant, elevator braking energy recovery) or with energy product ion resources installed for cost reduction and security reasons. Finally, they may also have energy storage resources, which could have been installed to build flexibility or for any other reason. Part or all of the stored energy capacity can then be used to reduce operational costs. Incentives to reduce or shift energy consumption in time must be considered with respect to the main objectives (and other cost factors) of the consuming organization. The very first thing to do is to characterize the available or potential sources of flexibility and how they could be used to make gains in terms of energy, revenues and cost savings, or environmental impact. • First, there may exist options for definitive savings of energy with no significant impact on the process for which the energy is used. In general, such savings will be doable provided they have an "acceptable" impact on the process or on its outcome. For example, the capacity to slightly dim lights in an elevator enables direct and definitive energy savings. Such dimming is acceptable if it does not occur too often. • Delays in consumption are possible when a given activity can be delayed (or performed in advance) or, more generally, when savings are possible at a given time but at the expense of further consumption before or after this time. For example, if enough water is available in a water tower, one can delay for a while the pumping of water into the water tower. At some point, however, pumping will be needed to ensure the water tower gets enough water to serve the local customers. Similarly, highly consuming activities in a manufacturing plant might be avoided during a given interval of time, provided these activities are not time-critical and the corresponding products are available in stock. At some point, however, it will become necessary to perform these activities, and consume the corresponding amount of energy to replenish the stock. • If energy storage (e.g., in batteries, in the form of hot water, etc.) is possible, then the stored energy can be used to provide an apparent consumption flexibility. For example, part of the energy stored in the battery of an elevator can be used to temporarily operate the elevator with no other impact on the elevator’s process. Considered separately, such sources of flexibility induce very different optimization models: multi-criteria regulation; scheduling with energy resource constraints and costs; energy flow optimization. Things get more complex when these sources of flexibility coexist and when multiple actors, each with its own constraints and objectives, share the same energy network. Practical optimization problems will be presented, using examples from two European projects (Arrowhead and Ambassador) and from the two PhD theses of Chloé Desdouits "Reduction of electricity consumption peaks and optimization problems induced on the demand side" and Peter Pflaum "Energy management strategies for smart grids".
RCLN 18/12/2017 Semantic similarity on transcriptional regulation literature, par Oscar Lithgow
Oscar Lithgow  
Salle B107, bâtiment B, Université de Villetaneuse
18/12/2017    12:30 - 14:00
Résumé :
Experimentally generated biological information needs to be organized and structured in order to become meaningful knowledge. However, the rate at which new information is being published makes manual curation increasingly unable to cope. Therefore, new curation strategies based on natural language processing are promising alternatives. Particularly, nowadays is improbable to consider all related research and reference every single piece of knowledge contained in the publication. Here is where we believe that computers and specifically, automatic natural language processing can help to inter-connect similar conveyed ideas among a collection of articles through discover ing semantically related sentences within a set of scientific articles and delivering those meaningful relations to the end user. Given our interest in applying such approaches to the benefit of curation of the biomedical literature, specifically about gene regulation in microbial organisms, we decided to also build a corpus with graded textual similarity evaluated by curators, and designed specifically oriented to our purposes.
A3 14/12/2017 Flots de liens pour la modélisation des interactions temporelles, par Matthieu Latapy
Matthieu Latapy, Lip6, Université Pierre et Marie Curie  
Salle B107, bâtiment B, Université de Villetaneuse
14/12/2017    12:15 - 13:30
Résumé :
Etudier la structure et la dynamique des interactions revêt un caractère crucial pour la compréhension de nombreux phénomènes et pour de nombreuses applications (détection d'événements dans du trafic, détection de fraudes, recommandation de produits, optimisation de réseaux, etc). La structure de telles interactions est étudiée en utilisant des graphes ou des réseaux (ensembles de noeuds et de liens) ; leur dynamique est étudiée en utilisant des signaux ou des séries temporelles (variations d'une propriété au cours du temps) ; pour étudier la dynamique de leur structure, on utilise des séquences de graphes. Toutefois, ces approches ne capturent que de façon très limitée la nature à la fois structurelle et temporelle des interactions, qui nécessite un cadre spécifique. Nous présentons ici une généralisation des graphes, que nous appelons des flots de liens, permettant un traitement cohérent des deux aspects. Nous obtenons un langage pour l'étude directe des séquences d'interactions, similaire à celui des graphes pour l'étude des relations.
CALIN 12/12/2017 A graph-based method to randomly generate subgroups of free groups, par Pascal Weil
Pascal Weil  
Salle B107, bâtiment B, Université de Villetaneuse
12/12/2017    15:00 -
Résumé :
The study of random algebraic objects sheds a different light on these objects, which complements the algebraic and the algorithmic points of view. When it comes to finitely generated subgroups of free groups, we have a remarkable graphical representation called the Stallings graph: the Stallings graph of a subgroup H is a finite labeled graph uniquely associated with H, efficiently computed from a set of generators of H (say, given as reduced words), and from which one can efficiently compute many invariants of H. I will discuss enumerating and randomly generating finitely generated subgroups of free groups, for the distribution given by Stallings graphs: for each positive integer n, one considers the finite number of subgroups whose Stallings graph has n vertices, and one considers the uniform distribution on that set. This requires understanding the combinatorial structure of Stallings graphs, which are interesting objects per se. I will also exhibit natural properties of subgroups which are `generic' for this distribution. This is joint work with F. Bassino (LIPN) and C. Nicaud (LIGM)
CALIN 21/11/2017 On the polynomial part of a restricted partition function, par Karl Dilcher
Karl Dilcher  
Salle B107, bâtiment B, Université de Villetaneuse
21/11/2017    11:00 -
Résumé :
We prove an explicit formula for the polynomial part of a restricted partition function, also known as the first Sylvester wave. This is achieved by way of some identities for higher-order Bernoulli polynomials, one of which is analogous to Raabe's well-known multiplication formula for the ordinary Bernoulli polynomials. As a consequence of our main result we obtain an asymptotic expression of the first Sylvester wave as the coefficients of the restricted partition grow arbitrarily large. (Joint work with Christophe Vignat).
CALIN 13/06/2017 Opérades des cliques décorées, par Samuele Giraudo
Samuele Giraudo  
Salle B107, bâtiment B, Université de Villetaneuse
13/06/2017    10:30 -
Résumé :
Nous proposons une construction fonctorielle de la catégorie des magmas unitaires vers celle des opérades non symétriques. Cette construction munit l'espace des configurations de diagonales décorées dans les polygones d'une structure d'opérade. On obtient ainsi diverses nouvelles opérades sur des sous-familles particulières de tels polygones : configurations sans croisement, configurations non imbriquées, configurations de Motzkin, etc. Nous montrons aussi comment cette construction permet de donner des définitions alternatives d'opérades déjà connues comme l'opérade des simples et doubles multi-tiles (provenant de la théorie des langages) et l'opérade de gravité.
AOC 30/05/2017 Combinatorial optimization problems in networks, par Nelson Maculan
Nelson Maculan, Federal University of Rio de Janeiro  
Salle B107, bâtiment B, Université de Villetaneuse
30/05/2017    12:30 - 13:30
Résumé :
We present optimization models with a polynomial number of variables and constraints for combinatorial optimization problems in networks: optimum elementary cycles (whose traveling salesman problem), optimum elementary paths even in a graph with negative cycles, and optimum trees (whose Steiner tree problem) problems. Computational results for the Steiner tree problem are also presented.
CALIN 23/05/2017 Magouilles diverses pour les machines à signaux, par Thierry Monteil
Thierry Monteil  
Salle B107, bâtiment B, Université de Villetaneuse
23/05/2017    14:00 -
Résumé :
Les machines à signaux sont un modèle de calcul déterministe dont espace et temps sont continus.

Si les accumulations d'événements sont interdites, ce modèle est connu pour être équivalent au modèle de BlumShubSmale linéaire. Nous construirons dans ce cadre un oracle universel optimal (en nombre de vitesses et de paramètres irrationnels). Nous verrons comment jouer au billard permet semi-décider l'algébricité d'un nombre réel alors que c'est impossible dans le modèle BSS-linéaire. Nous verrons comment modifier légèrement le modèle pour obtenir un modèle équivalent au modèle BSS standard.

Lorsque l'on permet aux accumulations d'événements de produire un signal, nous verrons, en jouant sur l'alternance discret/continu, comment construire des machines dont le pouvoir dépasse largement les modèles de calcul usuels, en particulier, nous construirons

  • une "courbe de Peano" c'est a dire une surjection de [0,1] dans [0,1]^2.
  • un "oracle universel continu", c'est à dire un machine à un paramètre M(p) telle que toute suite N->[0,1] est generèe un certain M(p).
  • une "fonction analytique universelle", c'est à dire une machine avec 2 parametres t,x telle que pour toute fonction analytique f de rayon de convergence >1, il existe t tel que f(x)=M(t,x) pour tout x dans [-1,1], en particulier, on peut calculer les fonctions exp(x), sin(), en déplaçant un curseur.
  • aussi, on peut prendre en compte la géométrie du modèle dans la formulation même de ce que peut "calculer" (ou "dessiner") une machine, pas seulement un booléen, un entier ou un réel comme dans le cas discret. Étant donnée une machine M, si certains types de collisions sont coloriés en rouge, l'ensemble de leurs accumulations au temps 1 est un compact. Il se trouve que cette restriction est la seule : il existe une machine à un parametre M(p) telle que pour tout compact K inclus dans [0,1], il existe p dans [0,1] tel que l'ensemble des accumulations rouges de M(p) au temps 1 est K.

L'exposé sera informel et sa compréhension ne nécessitera pas de prérequis.

A3 11/05/2017 Accountable classification without frontiers, par Khaled Belahcen
Khaled Belahcen, LGI, CentraleSupelec  
Salle B107, bâtiment B, Université de Villetaneuse
11/05/2017    12:15 - 13:30
Résumé :
We address the problem of multicriteria ordinal sorting through the lens of accountability, i.e. the ability of a human decision-maker to own a recommendation made by the system. We put forward a number of model features that would favor the capability to support the recommendation with a convincing explanation. To account for that, we design a recommender system implementing and formalizing such features. This system outputs explanations defined under the form of specific argument schemes tailored to represent the specific rules of the model. At the end, we discuss possible and promising argumentative perspectives.
AOC 09/05/2017 Derivative-Free Line search Methods for Solving Integer Programming Problems, par Francesco Rinaldi
Francesco Rinaldi  
Salle B107, bâtiment B, Université de Villetaneuse
09/05/2017    12:30 - 13:30
Résumé :
In this talk, we describe some derivative-free methods for integer programming problems with both bound constraints on the variables and general nonlinear c onstraints. The approaches combine linesearches with a specific penalty approach for handling the nonlinear constraints. The use of both suitable generated search directions and specific stepsizes in the linesearch guarantee that all the points are generated in the integer lattice. We analyze the theoretical properties of the methods and show extensive numerical experiments on both bound constrained and nonlinearly constrained problems.
A3 27/04/2017 RoSTBiDFramework: Optimised Framework based on Rough Set Theory for Big Data Pre- processing in Certain and Imprecise Contextsble, par Zeineb Chelly
Zeineb Chelly , Aberystwyth University, Wales, UK  
Salle B107, bâtiment B, Université de Villetaneuse
27/04/2017    12:30 - 13:45
Résumé :
Over the last decades, the amount of data has increased in an unprecedented rate, leading to a new terminology: "Big Data". Big data are specified by their Volume, Variety, Velocity and by their Veracity/Imprecision. Based on these 4V specificities, it has become difficult to quickly acquire the most useful information from the huge amount of data at hand. Thus, it is necessary to perform data (pre-)processing as a first step. In spite of the existence of many techniques for this task, most of the state-of-the-art methods require additional information for thresholding and are neither able to deal with the big data veracity aspect nor with their computational requirements. This project's overarching aim is to fill these major research gaps with an optimised framework for big data pre-processing in certain and imprecise contexts. Our approach is based on Rough Set Theory (RST) for data pre-processing and Randomised Search Heuristics for optimisation and will be implemented under the Spark MapReduce model. The project combines the expertise of the experienced researcher Dr Zaineb Chelly Dagdia in machine learning, rough set theory and information extraction with the knowledge in optimisation and randomised search heuristics of the supervisor Dr Christine Zarges at Aberystwyth University. Further expertise is provided by internal and external collaborators from academic and non-academic institutions, namely Lebbah and Azzag (University of Paris 13), Shen (University of Aberystwyth), Tino (University of Birmingham), Merelo (University of Granada) and an industrial partner from France.
A3 21/04/2017 Complex network analysis in ubiquitous and social environments, par Martin Atzmueller
Martin Atzmueller, University of Kassel, Faculty of Electrical Engineering/Computer Science  
Salle B107, bâtiment B, Université de Villetaneuse
21/04/2017    15:00 - 16:30
Résumé :
In the world of today, a variety of interaction data of humans, services and systems is generated, e.g. , by sensors and social media. This enables the observation and capture of physical and social activities, and subsequent extended analysis of interactions, structures and patterns covering both online and offline contexts. This talk focuses on behavioral analytics in social media and the physical world, and presents exemplary methods and results in the context of real-world systems. Specifically, we focus on the grounding and analysis of behavior, interactions and complex structures emerging from heterogeneous data, and according modeling approaches using complex network analysis.
AOC 18/04/2017 Deriving differential approximation results for k-CSPs from combinatorial designs, par Sophie Toulouse
Sophie Toulouse, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
18/04/2017    12:30 - 13:30
Résumé :
Given two integers q, k ? 2, k-CSP?q is the unconstrained optimization problem in which variables have domain Z_q and the goal is to optimize a weighted sum of constraints, each acting on at most k of the variables. Standard inapproximability results for Max-k-CSP?q often involve balanced k-wise independent distributions over Z_q or rather equivalently, orthogonal arrays of strength k over Z_q. We here illustrate how combinatorial designs are a relevant tool in order to establish approximation results for k-CSP?q with respect to the differential approximation measure, which compares the distance between the approximate value and the worst solution value to the instance diameter. First, connecting the average differential ratio to orthogonal arrays, we deduce that this ratio is ?(1/n^(k/2)) when q = 2, ?(1/n^(k-1)) when q is a prime power and 1/q^k on (k+1)-partite instances. We also consider pairs of arrays that can be viewed as some constrained decomposition of balanced k-wise independent functions. We exhibit such pairs that allow when q > k to reduce k-CSP?q to k-CSP?k with an expansion 1/(q?k/2)^k on the approximation guarantee. This implies together with the result of [Yuri Nesterov, Semidefinite relaxation and nonconvex quadratic optimization, Optimization Methods and Software, 9 (1998), pp. 141–160] a lower approximability bound of 0.429/(q ? 1)^2 for 2-CSP?q. Similar designs also allow to establish that every Hamming ball with radius k provides a ?(1/n^k)-approximation of the instance diameter.
CALIN 11/04/2017 Utilisation avancée de Maple : calcul parallèle et interfaçage avec des bibliothèques externes, par Nicolas Gachadoit et Nicolas Cottereau
Nicolas Gachadoit et Nicolas Cottereau  
Salle B107, bâtiment B, Université de Villetaneuse
11/04/2017    14:00 -
Résumé :
Maple possède plusieurs milliers de fonctions, mais certains calculs spécifiques peuvent nécessiter l'utilisation de bibliothèques externes. Par ailleurs, les ordinateurs n'évoluent plus tellement dans le sens d'une augmentation de la fréquence des processeurs mais dans le sens d'une augmentation du nombre de c?urs de calcul. Cette présentation (par Nicolas Gachadoit) détaillera les fonctionnalités de Maple permettant de réaliser des calculs parallèles et de s'interfacer avec du code écrit dans d'autres langages. Il y aura également une présentation rapide (par Nicolas Cottereau) de quelques fonctionnalités de la plateforme Maple dédiée pour l?enseignement.
CALIN 28/03/2017 Phase Transition Threshold for Random Graphs and 2-SAT using Degree Constraints, par Sergey Dovgal
Sergey Dovgal  
Salle B107, bâtiment B, Université de Villetaneuse
28/03/2017    14:00 -
Résumé :
We show that by restricting the degrees of the vertices of a graph to an arbitrary set ?, the threshold ?(?) of the phase transition for a random graph with n vertices and m = ?(?).n edges can be either accelerated (e.g., ?(?) approx 0.38 for ? = {0,1,4,5}) or postponed (e.g., ?(?) approx 0.95 for ?={1,2,50}) compared to a classical Erd?s?Rényi random graph where ?(N)=1/2. We investigate different graph statistics inside the critical window of transition (planarity, diameter, longest path...). We apply our results to a 2-SAT model with restricted literal degrees: the number of clauses that each literal is incident to belongs to the set ?. We prove a lower bound for the probability that a formula with n variables and m=2.?(?) n clauses is satisfiable. This probability is close to 1 for the subcritical regime m=2.?.n.(1-μ.n-1/3), μ to ∞ and improves/generalizes the lower bound of Bollobás, Borgs, Chayes, Kim, and Wilson. This shows how the phase transition threshold for 2-SAT moves if we change the degrees of the literals. Joint work with Vlady Ravelomanana.
CALIN 14/03/2017 Géométrie combinatoire : densité d'hypergraphes et méthode probabiliste, par Xavier Goaoc
Xavier Goaoc  
Salle B107, bâtiment B, Université de Villetaneuse
14/03/2017    14:00 -
Document attaché
Résumé :
Un hypergraphe à n sommets dont aucune projection sur k sommet n'est complète a au plus O(n^{k-1}) arêtes. Ce résultat, découvert simultanément par Sauer, Vapnick-Chervonenkis et Perles-Shelah au début des années 1970, est fondamental en apprentissage. En géométrie combinatoire et algorithmique, il permet souvent de contrôler la complexité (globale) d'une structure par sa "densité" locale. J'introduirai à ce mécanisme avant de présenter quelques extensions récentes, obtenues conjointement avec Boris Bukh (https://arxiv.org/abs/1701.06632), qui permettent un controle plus fin de la complexité. L'exposé ne supposera aucune connaissance préalable et un des ingrédients sera une construction probabiliste.
AOC 07/03/2017 Valid quadratic inequalities for convex and some non-convex quadratic sets, par Julio César Góez
Julio César Góez  
Salle B107, bâtiment B, Université de Villetaneuse
07/03/2017    11:30 - 12:30
Résumé :
In recent years, the generalization of Balas disjunctive cuts for mixed integer linear optimization problems to mixed integer non-linear optimization problems has received significant attention. Among these studies, mixed integer second order cone optimization (MISOCO) is a special case. For MISOCO one has the disjuncti ve conic cuts approach. That generalization introduced the concept of disjunctive conic cuts (DCCs) and disjunctive cylindrical cuts (DCyCs). Specifically, it showed that under some mild assumptions the intersection of those DCCs and DCyCs with a closed convex set, given as the intersection of a second order cone and an affine set, is the convex hull of the intersection of the same set with a linear disjunction. The key element in that analysis is the use of pencils of quadrics to find close forms for deriving the DCCs and DCyCs. In this talk we present an overview of the DCCs main results and we use the same approach to show the existence of valid conic inequalities for hyperboloids and non-convex quadratic cones when the disjunction is defined by parallel hyperplanes. Joint work with Miguel F. Anjos.
RCLN 06/03/2017 Automatic Deception Detection in Text Applying Topic Modeling Algorithms, par Hiram Calvo
Hiram Calvo, Centro de Investigación en Computación, IPN  
Salle B107, bâtiment B, Université de Villetaneuse
06/03/2017    14:00 - 15:00
Résumé :
We deal with deceptive text identification by using different kinds of features: a continuous semantic space model based on latent Dirichlet allocation topics (LDA), one-hot representation (OHR), syntactic information from syntactic n-grams (SN), and lexicon-based features using the linguistic inquiry and word count dictionary (LIWC). We will present experiments with several combinations of these features were tested to assess the best source(s) for deceptive text identification aiming to present a state of the art performance. We conducted our tests on three different available corpora: a corpus consisting of 800 reviews about hotels, a corpus consisting of 600 reviews about controversial topics, and a corpus consisting of 236 book reviews. Additionally, we present an analysis on which features lead to either deceptive or truthful texts, finding that certain words can play different roles (sometimes even opposing ones) depending on the task being evaluated. We will present results of experiments in one-domain setting by training and testing our models separately on each dataset (with fivefold cross-validation); in a mixed-domain setting by merging all datasets into one large corpus (again, with fivefold cross-validation), and finally, with cross-domain setting: using one dataset for testing and a concatenation of all other datasets for training.
AOC 02/03/2017 On big data, optimization and learning, par Prof. Andrea Lodi
Prof. Andrea Lodi, Department of Mathematics and Industrial Engineering - École Polytechnique de Montréal  
Salle B107, bâtiment B, Université de Villetaneuse
02/03/2017    12:30 - 13:30
Résumé :
In this talk I review a couple of applications on Big Data that I personally like and I try to explain my point of view as a Mathematical Optimizer -- especially concerned with discrete (integer) decisions -- on the subject. I advocate a tight integration of Machine Learning and Mathematical Optimization (among others) to deal with the challenges of decision-making in Data Science. For such an integration I try to answer three questions: 1) what can optimization do for machine learning? 2) what can machine learning do for optimization? 3) which new applications can be solved by the combination of machine learning and optimization?
RCLN 20/02/2017 L’évolution des bases de connaissances RDF, par Fatma Chamekh
Fatma Chamekh  
Salle B107, bâtiment B, Université de Villetaneuse
20/02/2017    14:00 - 15:00
Résumé :
En 2006, Tim Berners-Lee a présenté le web de données ou données liées (Linked data web of data) comme une nouvelle perspective du web sémantique. L'idée est de privilégier la publication des données structurées sur le web, sous forme d'un réseau global d'informations, en les reliant les unes aux autres. Cependant, des nouveaux jeux de données sont créés ou d’autres sont mises à jour. D’où, les bases de connaissances RDF ont besoin d’évoluer. Dans ce séminaire, je présenterai mes travaux de recherche qui porte sur l’évolution des bases de connaissances RDF en se focalisant sur la qualité des données et la gestion des versions. Dans un premier temps, j’exposerai mon travail de thèse. Il s’agit d’une approche pluridisciplinaire qui allie le paradigme agent aux technologies du web sémantique. Cette approche emploie les capacités cognitives et réactives des agents pour gérer la qualité des données et la gestion des versions. Dans un deuxième temps, je présenterai un bref aperçu sur mes travaux de recherche actuels.
AOC 07/02/2017 Reformulations de programmes quadratiques convexes en nombres entiers, par Dominique Quadri
Dominique Quadri, Université Paris-Sud  
Salle B107, bâtiment B, Université de Villetaneuse
07/02/2017    12:30 - 13:30
Résumé :
La programmation quadratique en nombres entiers trouve de nombreuses applications dans le monde réel. Il semble important de développer des méthodes de résolution exactes permettant de résoudre en des temps CPU limités de tels problèmes. Or de nos jours les solveurs de programmation linéaire sont de plus en plus efficaces. C'est pourquoi cet exposé est axé sur des reformulations de programmes quadratiques en variables entières en programmes linéaires.
A3 02/02/2017 Complétion de valeurs manquantes à l'aide d'un surfeur aléatoire, par François Rioult
François Rioult, GREYC Université de Caen  
Salle B107, bâtiment B, Université de Villetaneuse
02/02/2017    12:15 - 13:30
Résumé :
Dans les contextes réels, des valeurs manquantes figurent dans les données et il est possible d'obtenir des informations contextuelles expliquant l'absence de valeur : y-a-t-il une valeur spécifique pour un autre attribut ? y-a-t-il une autre valeur manquante ? etc. Ces informations contextuelles peuvent être organisées sous forme de graphe, où un surfeur aléatoire fera émerger l'explication la plus probable pour cette valeur manquante. Cette explication donne des indications sur une potentielle complétion.
A3 26/01/2017 Fouille de données déclarative, par Benjamin Negrevergne
Benjamin Negrevergne, Lamsade Paris Dauphine  
Salle B107, bâtiment B, Université de Villetaneuse
26/01/2017    12:15 - 13:30
Résumé :
Une grande variété de techniques de fouille de données ne sont disponibles que sous la forme d'algorithmes en programmation impérative. Ces algorithmes sont difficiles à (ré-)utiliser et difficiles à adapter aux besoins de leurs utilisateurs. Une proposition récente vise à utiliser le paradigme de la programmation par contraintes pour obtenir des formulations plus déclaratives de ces techniques. Cette approche offre de nombreux avantages, comme celui de pouvoir incorporer facilement des connaissances métier au sein du processus de fouille. Dans cette présentation, j'expliquerai comment formuler et résoudre efficacement des problèmes de fouille de données grâce à la programmation par contraintes. Je parlerai également des limites de cette approche pour la formulation de problèmes de fouille de données structurées (fouille de séquences ou graphes) ou par la formulation de critères d'intérêts complexes (combinaisons de contraintes, préférences) ainsi que de mes contributions dans ce domaine.
AOC 24/01/2017 Reformulations for Mixed-Integer Nonlinear Programs: a surprisingly simple one with surprisingly good results in (quite) a few different applications, par Antonio Frangioni
Antonio Frangioni  
Salle B107, bâtiment B, Université de Villetaneuse
24/01/2017    12:30 - 13:30
Résumé :
We describe a quite long line of research about the Perpective Reformulation of certain Mixed-Integer NonLinear Programs, which started with a total serendipity moment motivated by trying to prove wrong a referee who was in fact right but for the wrong reasons. The research was brought forward in part by a series of othe r developments motivated by factors such as the need to finding another application to publish the first paper, the need of fending off competing research teams, and finding a good idea as a by-product of an original one that would never work. All this brought us to a Project-and-Lift approach to certain projected reformulations of the Perspective Reformulation which seems to be one of the few authentic violations of the "no free lunch principle": an easy reformulation of a MIQP with the very same size and structure as the original one but with a substantially stronger bound. Apart from providing an overview on a recent and potentially interesting research field in MINLP, we hope that this talk can motivate the audience to making more errors and looking at them with more interest.
CALIN 09/12/2016 Double regularization of polyzetas at negative multi-indices and rational extensions (soutenance de thèse), par Quoc Hoan Ngo
Quoc Hoan Ngo  
Salle B107, bâtiment B, Université de Villetaneuse
09/12/2016    16:00 -
Résumé :
In this PhD thesis are studied the polylogarithms and the harmonic sums at non-positive (i.e., weakly negative) multi-indices. General results about these objects in relation with Hopf algebras are pr ovided. The technics exploited here are based on the combinatorics of noncommmutative generating series relative to the Hopf phi-huffle algebra. Our work will also propose a global process to renormalize divergent polyzetas. Finally, we will apply these ideas to non-linear dynamical systems with singular inputs.

The jury will be composed of: Gérard Duchamp, Hoang Ngoc Minh (directeurs), Sylvie Paycha, Dominique Manchon (rapporteurs), Karol Penson, Vincent Rivasseau, Loic Foissy, Christophe Tollu.

CALIN 09/12/2016 Développement asymptotique des sommes harmoniques (soutenance de thèse), par Van Chiên Bui
Van Chiên Bui  
Salle B107, bâtiment B, Université de Villetaneuse
09/12/2016    14:30 -
Résumé :
En abordant les nombres spéciaux comme les sommes harmoniques ou les polyzêtas sous leur aspect combinatoire, nous introduisons d'abord la définition d'un produit entre mots, dit produit de quasi-mélange q-déformé, une généralisation des produits de mélange et de quasi-mélange, ce qui nous permet de construire des structures complètes d'algèbre de Hopf en dualité. En même temps, nous construisons des bases en dualité, contenant des bases de transcendance associées aux mots de Lyndon, et des formules explicites sur lesquelles les sommes harmoniques, les polyzêtas ou les polylogarithmes sont indexés et représentés par la factorisation de la série génératrice noncommutative diagonale. De cette façon, en identifiant les coordonnées locales, nous trouvons des relations polynomiales homogènes, en poids, entre les polyzêtas indexés par ces bases. Enfin, nous déterminons les développements asymptotiques des sommes harmoniques, indexées aussi par ces bases, grâce à leur série génératrice et à la formule d'Euler Maclaurin. Pour accompagner cette étude théorique, nous proposons des algorithmes et un package en Maple afin de calculer des bases, la structure des polyzêtas et des développements asymptotiques des sommes harmoniques.

Le jury sera composé de Gérard Duchamp, Hoang Ngoc Minh, (co-directeurs), Jacky Cressson, Loïc Foissy, (rapporteurs), Sylvie Paycha, Joris van der Hoeven, Daniel Barsky, Christophe Tollu (examinateurs).

CALIN 29/11/2016 Une analyse asymptotique des polyominos digitalement convexes., par Olivier Bodini
Olivier Bodini  
Salle B107, bâtiment B, Université de Villetaneuse
29/11/2016    14:00 -
Résumé :
Dans cet exposé, nous montrerons comment des techniques élémentaires (transformées de Mellin) en combinatoire analytique permettent d'obtenir des résultats assez surprenants sur les polyominos. En particulier, si l'on savait correctement énumérer les polyominos digitalement convexes, nous saurions si l'hypothèse de Riemann est vraie !
RCLN 28/11/2016 Semantically enriched methods for next generation microblog message fine-grained geolocalization, par Laura Di Rocco
Laura Di Rocco, University of Genoa / visiting PhD Student at Paris Descartes University (LIPADE)  
Salle B107, bâtiment B, Université de Villetaneuse
28/11/2016    14:00 - 15:00
Résumé :
Consistent user-generated data represent a valuable source for the extraction of new types of information patterns and knowledge. The multifaceted nature of user-generated data, along with its geographic component, is being exploited to better understand social dynamics and propagation of information. Social media activities can be associated with both an explicit and an implicit geographic information component. Consider, for instance, Twitter as a typical example. In this case, georeferencing information can be explicitly available as metadata, such as the user profile location and the GPS coordinates of the device from which the activity is performed. By contrast, implicit georeferencing information can be inferred, with variable degree of confidence, by the message content itself, which may contain images, names of entities with known spatial location, or by the social relationships and interactions among users. Our focus is on inferring the tweeting location (i.e., the position of the user when the tweet was sent) rather than the user home location. Since explicit tagging is used only in a small percentage of tweets, we will use geospatial information implicit in the messages to improve the resolution of the georeferencing process. With the aim of fully exploiting the (explicit and implicit) fine-grained georeferencing information made available by social media, the project relies on semantically enhanced and refined crowdsourced geospatial data to extract fine-grained implicit geoinformation contained in tweet contents. Short Bio: Laura Di Rocco is a PhD Student at University of Genoa and a visiting PhD Student at Paris Descartes University (LIPADE). Her research interests are in the areas of geospatial data and text mining on social media.
CALIN 15/11/2016 On Generalized Hypergeometric Solutions of Linear Differential Systems of First Order, par Suzy Maddah
Suzy Maddah  
Salle B107, bâtiment B, Université de Villetaneuse
15/11/2016    10:30 -
Résumé :
In this talk, we consider linear differential systems of first order (equivalently linear differential equations of arbitrary order), and we question whether they can be solved in terms of generalized hypergeometric functions. This question is motivated by the many properties of the latter which arise in physics and combinatorics. It has been tackled in the literature for second-order differential equations, namely Bessel's, Whittaker's, Kummer's, and Gauss's. We propose a new algorithm which surpasses the restrictions on the dimension of the system, and equivalently on the order of the equation. This is a joint work with Frédéric Chyzak.
RCLN 14/11/2016 Identification des expressions poylexicales et analyse syntaxique en dépendances, par Mathieu Constant
Mathieu Constant, Université de Lorraine, ATILF  
Salle B107, bâtiment B, Université de Villetaneuse
14/11/2016    14:00 - 15:00
Résumé :
Les expressions polylexicales (EP) sont des séquences formées de plusieurs mots se caractérisant par un certain degré de non-compositionalité que ce soit au niveau morphologique, lexical, syntaxique, sémantique ou/et pragmatique. Leur identification est cruciale pour les différentes applications du traitement automatique des langues. Dans cet exposé, nous nous intéressons à l’intégration de l’identification des EP au sein de l’analyse syntaxique en dépendances statistique. Après avoir évoqué les différents défis liés à l’identification automatique des EP, nous aborderons ce sujet en essayant de répondre à deux problématiques: (1) trouver une représentation la plus riche possible des exp ressions polylexicales au regard de l’analyse syntaxique; (2) adapter les algorithmes d’analyse existants pour prédire de manière jointe l’analyse lexicale et syntaxique d’une phrase dans cette représentation. En particulier, nous montrerons de nouvelles représentations factorisées sur deux dimensions, ainsi que de nouveaux algorithmes d’analyse syntaxique intégrant des mécanismes spécifiques pour l’identification des EP.
AOC 18/10/2016 Lower bounds in resource constrained shortest path algorithms, par Axel Parmentier
Axel Parmentier  
Salle B107, bâtiment B, Université de Villetaneuse
18/10/2016    12:30 - 13:30
Résumé :
Resource constrained shortest path problems arise naturally as pricing sub-problems of column generation approaches to a wide range of routing and scheduling problems. The algorithms for these problems rely on dominance relations between paths to discard partial solutions in an enumeration of all the paths. It is well known that the use of bounds on paths resources in addition to dominance relations strongly accelerates these algorithms. Nonetheless, there is still no standard procedure to build such bounds in non-linear or stochastic settings. We provide such a bounding procedure and sho w its efficiency on several deterministic and stochastic path problems. Besides, enumeration algorithms exhibit poor performances when the number of constraints increases. We show that using sets of bounds instead of single bounds enable to discard more paths and thus to tackle better with these difficult instances. Finally, we prove the relevance of these procedures in the context of column generation on industrial instances of the airline crew pairing problem.Â
RCLN 17/10/2016 Framester: A Wide Coverage Linguistic Linked Data Hub, par Mehwish Alam
Mehwish Alam, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
17/10/2016    14:00 - 15:00
Résumé :
Semantic web applications leveraging NLP can benefit from easy access to expressive lexical resources such as FrameNet. However, the usefulness of FrameNet is affected by its limited coverage and non-standard semantics. The access to existing linguistic resources is also limited because of poor connectivity among them. We present some strategies based on Linguistic Linked Data to broaden FrameNet coverage and formal linkage of lexical and factual resources. We created a novel resource, Framester, which acts as a hub between FrameNet, WordNet, VerbNet, BabelNet, DBpedia, Yago, DOLCE-Zero, as well as other resources. Framester is not only a strongly connected knowledge graph, but also applies a rigorous formal treatment for Fillmore's frame semantics, enabling full-fl edged OWL querying and reasoning on a large frame-based knowledge graph. We also describe Word Frame Disambiguation, an application that reuses Framester data as a base in order to perform frame detection from text, with results comparable in precision to the state of the art, but with a much higher coverage. Open issues and current research directions will be also presented.
CALIN 11/10/2016 Non-commutative differential equations and (some) geometrical hints, par Gérard Duchamp
Gérard Duchamp  
Salle B107, bâtiment B, Université de Villetaneuse
11/10/2016    14:00 -
Résumé :
On prendra appui sur les intégrales itérées des systèmes fuschsiens pour proposer une théorie des équations différentielles non-commutatives. Plusieurs surprises et cadeaux nous attendent dans cette exploration.
AOC 06/10/2016 Solving the Asymmetric Travelling Salesman Problem, par Luis Gouveia
Luis Gouveia , University of Lisbon, Faculty of Sciences, Dept. of Statistics and OR, CMAF CIO, Portugal  
Salle B107, bâtiment B, Université de Villetaneuse
06/10/2016    10:30 - 11:30
Résumé :
There are many ways of modelling the Asymmetric Traveling Salesman Problem (ATSP) and the related Precedence Constrained ATSP (PCATSP). In this talk we present new formulations for the two problems that can be viewed as resulting from combining precedence variable based formulations, with network flow based formulations. As suggested in [1], the former class of formulations permits to integrate linear ordering constraints. The motivating formulation for this work is a complicated and "ugly" formulation that results from the separation of generalized subtour elimination constraints presented in [2] (see also [1]). This so called "ugly" formulation exhibits, however, one interesting feature, namely the "disjoint subpaths" property that is further explored to create more complicated formulations that combine two (or three) "disjoint path" network flow based formulations and have a stronger linear programming bound. Some of these stronger formulations are related to the ones presented for the PCATSP in [3] and can be viewed as generalizations in the space of the precedence based variables. Several sets of projected inequalities in the space of the arc and precedence variables and in the spirit of many presented in [1] are obtained by projection from these network flow based formulations. Computational results will be given for the ATSP and PCATSP to evaluate the quality of the new models and inequalities. References: [1] L. Gouveia and P. Pesneau. On extended formulations for the precedence constrainted asymmetric traveling salesman problem. Networks, 48(2):77{89, 2006. [2] L. Gouveia and J. M. Pires. The asymmetric travelling salesman problem: On generalizations of disaggregated Miller-Tucker-Zemlin constraints. Discrete Applied Mathematics, 112:129{145, 2001. Joint work with Pierre Pesneau (University of Bordeaux), Mario Ruthmair (University of Vienna) and Daniel Santos (University of Lisbon)
CALIN 04/10/2016 Évaluation multi-précision rigoureuse de fonctions D-finies en Sage, par Marc Mezzarobba
Marc Mezzarobba  
Salle B107, bâtiment B, Université de Villetaneuse
04/10/2016    14:00 -
Document attaché
Résumé :
Je présenterai une implémentation en développement d'algorithmes d'évaluation numérique de fonctions D-finies (c.-à-d. solutions d'équations différentielles linéaires à coefficients polynomiaux), pour le logiciel de calcul formel libre SageMath. Ce nouveau package a vocation à remplacer NumGfun, un package un peu similaire pour Maple que j'ai présenté au séminaire CALIN il y a quelques années. Si le temps le permet, je dirai aussi quelques mots des algorithmes originaux utilisés. La fonctionnalité centrale de ce code est le « prolongement analytique numérique » d'une fonction D-finie, qui fournit une approximation de la matrice envoyant un jeu de conditions initiales en un point donné du plan complexe sur les conditions « initiales » qui définissent la même fonction au voisinage d'un autre point. Le prolongement analytique numérique permet de calculer des valeurs ou encore des approximations polynomiales de fonctions D-finies n'importe où sur leur surface de Riemann, des matrices de monodromie d'opérateurs différentiels, etc. Le code traite complètement le cas limite important de conditions initiales généralisées données en un point singulier régulier de l'opérateur. Il peut donc être utilisé pour calculer des matrices de connexion entre singularités régulières, ce qui est utile notamment en combinatoire analytique. Par ailleurs, il s'agit d'une implémentation rigoureuse, au sens où elle renvoie des intervalles qui (sauf bug !) contiennent à coup sûr le résultat mathématique exact.
CALIN 20/09/2016 Counting observables of colored tensor models, par Joseph Ben Geloun
Joseph Ben Geloun  
Salle B107, bâtiment B, Université de Villetaneuse
20/09/2016    14:00 -
Résumé :
Colored tensor models generate Feynman graphs representing discrete geometries. They form as an interesting approach of quantum gravity where discrete geometries represent quanta of spacetime. The coloring in tensor models improves a lot the topology type of these discrete structures and this helps a lot in their understanding. In my presentation, I will review (in a pedestrian way) their construction and then list basic properties of their observables. Recalling that an observable simply means in this context a convolution or contraction of tensors, observables of colored tensor models map to bi-partite colored graphs. A first question that one can address is can we enumerate these observables? I will explain how such an enumeration is possible and how it has lead us to an intriguing bijection with the counting of branched covers of the 2-sphere.
CALIN 20/09/2016 Shuffle d'arbres, par Eric Hoffbeck
Eric Hoffbeck  
Salle B107, bâtiment B, Université de Villetaneuse
20/09/2016    10:30 -
Résumé :
Les shuffles (battages) jouent un rôle important dans la compréhension du produit d'ensembles simpliciaux, qui intervient à de nombreux endroits en topologie algébrique. Récemment, une généralisation des ensembles simpliciaux a été introduite : les ensembles dendroidaux (on remplace les {0,1,...,p} (avec leur ordre total) par des arbres (avec leur ordre partiel)). La catégorie des ensembles dendroidaux est également munie d'un produit, où interviennent des shuffles d'arbres. Dans cet exposé, après une brève motivation topologique, j'introduirai cette notion de shuffles d'arbres, en donnant plusieurs définitions équivalentes et de nombreux exemples. Je présenterai ensuite quelques propriétés algébriques et combinatoires de ces shuffles. Mon exposé est basé sur un travail en commun avec Ieke Moerdijk.
CALIN 06/09/2016 Génération des alignements d'arbres, par Julien Courtiel
Julien Courtiel  
Salle B107, bâtiment B, Université de Villetaneuse
06/09/2016    14:00 -
Résumé :
L'alignement d'arbres est la généralisation naturelle de la notion classique d'alignement de séquences. Elle est utilisée dans de nombreux domaines, y compris pour la comparaison de structures secondaires d'ARN (ce qui nous intéressera aujourd'hui). Nous allons donc comprendre comment explorer l'espace des alignements d'arbres et comment déduire des algorithmes efficaces pour comparer les ARN. Cet exposé introduit ainsi les notions d'alignement de séquences et d'arbres et décrit le problème d'ambiguïté qui point quand nous voulons générer de manière correcte les alignements d'arbres. Pour résoudre ce problème d'ambiguïté dans le contexte des alignements d'arbres, nous donnons un schéma de décomposition sous la forme de grammaire sans contexte. Cela conduit à de nombreux résultats : propriétés statistiques sur les larges structures d'ARN, algorithmes efficaces d'échantillonnage... Ces travaux, en collaboration avec Cédric Chauve et Yann Ponty, illustrent le fait que la combinatoire peut être un puissant couteau suisse pour traiter des problèmes algorithmiques qui apparaissent dans de nombreux champs appliqués.
RCLN 11/07/2016 Abstraction, Entropy and Computing Formats, par Luis A. Pineda
Luis A. Pineda, Universidad Nacional Autónoma de México  
Salle B107, bâtiment B, Université de Villetaneuse
11/07/2016    14:00 - 15:00
Résumé :
In this talk a theory for the diagrammatic representation and computation of finite discrete functions and abstractions is presented. The theory is defined in terms of two basic operations that are computed directly on tables: the func- tional abstrac tion and the functional application or reduction. However, unlike the analogous operations of the lamba-calculus, these operations are not fully re- versible and the system has an inherent information loss. For this, abstractions have an associated entropy value that measures their degree of indeterminacy or information content. The theory is applied to the definition and construction of an associative memory, where the information is accessed by content, with its associated memory register, recognition and retrieval operations. A case study in visual memory with very promising preliminary results is presented. The overall theory suggests a comprehensive view or space of possible compu- tations that is defined in relation to (1) the trade-off between extensional and intensional forms of expressing information and (2) the formats employed in computations. This trade-off underlies the knowledge representation trade-off of articial intelligence and cognitive science.The computing formats, in turn, range from the linguistic format, whose paradigmatic case is the Turing Machine, to fully distributed formats including neural networks and the diagrammatic format.The view suggests that the trade-off between extensions and intensions is the manner in which the entropy of abstractions surface in the linguistic format. It also supports the case of direct representation in AI and the case of images in the imagery debate, and helps to clarify the opposition between symbolic and sub-symbolic computations. Finally, the implications of the view for learning, creativity, embodied and situated cognition, and for the distinction between "artificial" and "natural” computations are briefly discussed.
RCLN 20/06/2016 Towards narrative generation of spatial experiences in service robots, par Jorge Garcia Flores
Jorge Garcia Flores, RCLN, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
20/06/2016    14:00 - 15:00
Résumé :
We propose a first approximation to the generation of narrative experiences by a service robot. The goal of such narratives is to communicate in a brief, structured and natural way what the robot recently experienced while solving a task. We structure the narrative's elements into blocks guided by the spatial areas the robot visited. We also include a mechanism to mention failures, and template-based natural language generation. At this state of our research we include movement, manipulation and visual events. We evaluate our approach comparing the generated narratives with descriptions produced by humans after having followed the same robot's trajectory and performed the same robot's activities. We use the ROUGUE-L automatic evaluation metric and a survey in order to measure the narrative quality of the robot's description. Results show that while the robot generated narratives have close to human completeness scores, they still lack of readability and fluency.
CALIN 31/05/2016 Counting connected graphs with large excess, par Élie de Panafieu
Élie de Panafieu  
Salle B107, bâtiment B, Université de Villetaneuse
31/05/2016    14:00 -
Résumé :
We enumerate the connected graphs that contain a linear number of edges with respect to the number of vertices. So far, only first term of the asymptotics and a bound on the error were known (Bender Canfield McKay 1995, Pittel Wormald 2005, van der Hofstad Spencer 2006). We present a proof based on analytic combinatorics, i.e. generating function manipulations, and derive the complete asymptotic expansion.
MERCRED 25/05/2016 On the reconstruction of trees from their U-polynomial., par José Aliste-Prieto
José Aliste-Prieto, Universidad Andres Bello, Santiago du Chili  
Salle B107, bâtiment B, Université de Villetaneuse
25/05/2016    14:00 - 15:00
Résumé :
The U-polynomial of a graph was introduced by Noble and Welsh as a generalization of some invariants coming from Knot theory. It also generalizes the chromatic symmetric function of Stanley. In this talk, we will consider the problem of whether there exist non-isomorphic trees with the same U-polynomial (or,equivalently, with the same chromatic symmetric function). We will survey what is know about the U-polynomial and this problem. In particular, we will show how to recover some classic invariants from the U-polynomial and we exhibit several subclasses of trees for which a solution of this problem is known. FInally, we construct some non-isomorphic trees with "almost" the same U-polynomial, based on solutions of an old problem in Number theory due to Prouhet-Tarry-Escott.
RCLN 23/05/2016 Modèles neuronaux pour la traduction automatique, par Alexandre Allauzen
Alexandre Allauzen, LIMSI-CNRS  
Salle B107, bâtiment B, Université de Villetaneuse
23/05/2016    14:00 - 15:00
Résumé :
Les modèles neuronaux occupent aujourd'hui dans le traitement automatique des langues (TAL) une place importante car ils permettent grâce à leur caractère continu des avancées significatives dans de nombreux domaines applicatifs. Historiquement, les modèles de langue neuronaux ont été une des premières réalisations marquantes, avec des applications en reconnaissance automatique de la parole (RAP), puis à d'autres tâches complexes de modélisation linguistique, comme par exemple l'analyse syntaxique, l'estimation de similarité sémantique, les modèles d'alignement de mots et en traduction automatique statistique. L'exposé décrira les travaux menés au LIMSI-CNRS sur les réseaux neuronaux appliqués principalement à la traduction automatique: les modèles de langues n-grammes à grand vocabulaire, puis leur extension aux modèles de traduction et leur apprentissage discriminant.
MERCRED 18/05/2016 Vers la conception formelle de systèmes d’édition collaborative consistants , par Hanifa Boucheneb
Hanifa Boucheneb, Université Polytechnique de Montreal (Canada)  
Salle B107, bâtiment B, Université de Villetaneuse
18/05/2016    14:00 - 15:00
Résumé :
Les systèmes d’édition collaborative permettent à un groupe d’utilisateurs de partager et modifier des objets (textes, images, d ocuments XML, etc.) via le Web. Pour une meilleure réactivité aux opérations d’édition, ces systèmes sont en général basés sur la réplication des données. Chaque utilisateur a donc sa propre copie (locale) de l’objet qu’il peut modifier. Les modifications (opérations) locales sont ensuite propagées et intégrées aux autres copies. Un des défis majeurs de ces systèmes est d’assurer la consistance des données répliquées. Ce séminaire présentera et discutera les principales approches d’intégration des modifications non locales, proposées dans littérature. Il considérera ensuite les approches basées sur la transformation des opérations (OT) et montrera comment utiliser les méthodes formelles (model-checking symbolique et synthèse de contrôleur) pour vérifier si une approche OT assure la consistance des données répliquées et synthétiser une approche OT qui assure la consistance des données répliquées.
A3 12/05/2016 Agrégation souple et adaptative des graphes hétérogènes avec des attributs hétérogènes, par Amine Louati
Amine Louati, LAMSADE  
Salle B107, bâtiment B, Université de Villetaneuse
12/05/2016    12:15 - 13:30
Résumé :
In the enterprise context, people need to exploit, interpret and mainly visualize dierent types of interactions between heterogeneous objects. Graph model is an appropriate way to represent those interactions. Nodes represent the individuals or objects and edges represent the relationships between them. However, extracted graphs are in general heterogeneous (i.e., composed of different node attributes and different relationship types) and large sized which makes it diffcult to visualize and to analyze easily. An adaptive aggregation operation is needed to have more understandable graphs in order to allow users discovering underlyin g information and hidden relationships between objects. Existing graph summarization approaches such as k-SNAP are carried out in homogeneous graphs where nodes are described by the same list of attributes that represent only one community. The aim o f this work is to propose a general tool for graph aggregation which addresses both homogeneous and heterogeneous graphs. To do that, we develop a new soft and adaptive approach to aggregate heterogeneous graphs using the definition of Rough Set Theory (RST) combined with Formal Concept Analysis (FCA), the well known K-Medoids and the hierarchical clustering methods. Aggregated graphs are produced according to user-selected node attributes and relationships. To evaluate the quality of the obtained summaries, we propose two quality measures that evaluate respectively the similarity and the separability of groups based on the notion of common neighbor nodes. Experimental results demonstrate that our approach is effective for its ability to produce a high quality solution with relevant interpretations.
RCLN 02/05/2016 Neoveille, état d'avancement du projet, par Emmanuel Cartier
Emmanuel Cartier, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
02/05/2016    14:00 - 15:00
Résumé :
Neoveille est un projet financé par SPC qui vise à construire une plateforme de repérage, d'analyse et de suivi des néologismes sur gros corpus, en sept langues (français, portugais du Brésil, tchèque, grec, polonais, russe, chinois). Nous rappellerons les objectifs globaux du projet avant d'évoquer les différents composants de la plateforme dans le détail : récupération automatique de corpus en sept langues; repérage automatique des néologismes de forme; indexation dans le moteur de recherche et d'analyse. Finalement, nous évoquerons les pistes de travail à venir.
CALIN 19/04/2016 On Noncrossing Partitions for the Alternating Groups, par Henri Mühle
Henri Mühle  
Salle B107, bâtiment B, Université de Villetaneuse
19/04/2016    14:00 -
Résumé :
The lattice of noncrossing set partitions of an n-set can be seen as a subgraph of the Cayley graph of the symmetric group S generated by all transpositions. We mimic this construction for the alternating group A2n+1 generated by all 3-cycles. The resulting poset provides a rich new source of combinatorics coming from the alternating groups, which in some sense parallels the combinatorics behind the noncrossing set partitions. We present some enumerative and bijective results, and suggest an extension of this construction to all finite Coxeter groups. This is joint work with Philippe Nadeau.
CALIN 12/04/2016 Métriques extrémales et plongements de graphes, par Alfredo Hubard
Alfredo Hubard  
Salle B107, bâtiment B, Université de Villetaneuse
12/04/2016    15:00 -
Résumé :
Dans cet exposé je présenterai des résultats dans l' intersection de la géométrie Riemannienne et la topologie algorithmique. Plus précisément, je discuterai des manières effectives de planariser une surface triangulée, des problèmes de nombre de croisements, et de la "meilleure" métrique Riemannienne pour une surface. Si le temps le permet, je parlerai également des défis en haute dimension et des connections avec les nombres de faces des complexes simpliciaux.
CALIN 22/03/2016 Calculer dans un automate cellulaire unidirectionnel réversible : vers l'indécidabilité de la périodicité?, par Martin Delacourt
Martin Delacourt  
Salle B107, bâtiment B, Université de Villetaneuse
22/03/2016    14:00 -
Résumé :
On s'intéresse au parallèle entre 2 problèmes sur des modèles distincts d'automates. D'une part, les automates de Mealy (transducteurs lettre à lettre complets) qui produisent des semi-groupes engendrés par les transformations sur les mots infinis associées aux états. En 2013, Gillibert a montré que le problème de la finitude de ces semi-groupes était indécidable. En revanche la question est ouverte dans le cas où l'automate de Mealy produit un groupe. D'autre part, les automates cellulaires unidirectionnels pour lesquels la question de la décidabilité de la périodicité est ouverte. On peut montrer l'équivalence de ces problèmes. On fera un pas dans cette étude en montrant qu'il est possible de simuler du calcul Turing dans un automate cellulaire unidirectionnel réversible, rendant ainsi des problèmes de prédiction indécidables ainsi que la question de la périodicité partant d'une configuration finie.
AOC 22/03/2016 Combinatorial Optimization subject to PDE constraints, par Christoph Buchheim
Christoph Buchheim , Technische Universität Dortmund  
Salle B107, bâtiment B, Université de Villetaneuse
22/03/2016    12:30 - 13:30
Résumé :
We investigate a class of optimal control problems where the control parameters are binary variables, which are supposed to be static and probably subject to combinatorial constraints. Additionally, the problem contains state constraints involving semi-linear elliptic partial differential equations (PDEs). As an example, the binary variables may correspond to the activation of given heat sources attached to a metal sheet, the optimization problem then consists in switching on the smallest number of heat sources such that the point-wise temperature of the metal sheet is in a specified range. Our main result is that each state is a concave function in the binary control vector. This allows us to define an outer approximation scheme in which we alternate between the solution of a non-linear PDE and an integer linear program. Using this approach, we can solve instances on up to 2000 binary variables to global optimality.
RCLN 21/03/2016 Apprentissage partiel de dépendances syntaxiques et application au transfert cross-lingue, par Ophélie Lacroix
Ophélie Lacroix, LIMSI-CNRS  
Salle B107, bâtiment B, Université de Villetaneuse
21/03/2016    14:00 - 15:00
Résumé :
L'apprentissage supervisé est largement utilisé dans le domaine du TAL mais requiert l'exploitation de données correctement annotées. Nous nous intéressons en particulier au cas de l'analyse syntaxique en dépendances et montrons qu'il est possible d'apprendre un analyseur par transition à partir de données partiellement annotées. Ce procédé est notamment profitable dans le cas du transfert d'annotations cross-lingue pour lequel les informations syntaxiques (les dépendances) sont projetées d'une langue source (bien dotée) à une langue cible (peu dotée) via des liens d'alignements. Les données partiellement annotées générées à partir de cette méthode permettent d'appre ndre des analyseurs en dépendances pour les langues ciblées. Cette méthode simple de transfert obtient des performances qui rivalisent avec celles de méthodes état-de-l'art récentes, tout en ayant un coût algorithmique moindre.
CALIN 15/03/2016 Partitions d'entiers et groupes de Coxeter, par Mathias Pétréolle
Mathias Pétréolle  
Salle B107, bâtiment B, Université de Villetaneuse
15/03/2016    14:00 -
Résumé :
En 2009, Han a redécouvert et généralisé une identité due à Nekrasov et Okounkov, qui fait un lien entre d'un coté, les puissances de la fonction êta de Dedekind, et de l'autre les partages d'entiers et leurs longueurs d'équerres. Pour cela, il utilise la formule de Macdonald pour le système affine de racines de type A. Je montrerai comment, à l'aide de bijections, il est possible de démontrer des identités de Nekrasov-Okounkov pour d'autres types de systèmes de racines (type affine C et D notamment), et je présenterai les nouvelles formules des équerres qui en découlent. Dans une seconde partie, je présenterai la notion d'éléments cycliquement pleinement commutatifs dans les groupes de Coxeter, qui ont été introduits pour étudier une version cyclique d'un théorème de Matsumoto. Je montrerai ensuit comment, en utilisant la théorie des automates finis, on peut démontrer que la série génératrice de ces éléments est une fraction rationnelle, quelque soit le groupe de Coxeter considéré.
CALIN 01/03/2016 Algèbre de Hopf cambrienne, par Grégory Châtel
Grégory Châtel  
Salle B107, bâtiment B, Université de Villetaneuse
01/03/2016    14:00 -
Résumé :
En 1998, Loday et Ronco décrivent une algèbre de Hopf combinatoire dont la base est indicée par des arbres binaires. Cette algèbre possède de nombreux liens avec divers résultats antérieurs. Son produit est en particulier lié aux intervalles du treillis de Tamari, structure d'ordre partiel dont les éléments sont des arbres binaires. En 2006, Reading définit la notion de treillis cambrien d'un groupes de Coxeter. Le treillis Cambrien généralise l'ordre de Tamari en utilisant des structures arborescentes qui généralisent les arbres binaires : les arbres cambriens. Une question naturelle se pose alors : est-il possible de généraliser l'algèbre de Hopf de Loday-Ronco aux arbres cambriens ? Dans cette présentation, j'expliquerai les résultats que nous avons obtenus avec Vincent Pilaud sur les arbres cambriens en type A.
RCLN 18/02/2016 Sampled Weighted Min-Hashing for Large-Scale Topic Mining, par Ivan Vladimir MEZA
Ivan Vladimir MEZA, UNAM, Mexique  
Salle B107, bâtiment B, Université de Villetaneuse
18/02/2016    14:00 - 15:00
Résumé :
Sampled Weighted Min-Hashing (SWMH) is a randomized approach to automatically mine topics from large-scale corpora. SWMH generates multiple random partitions of the corpus vocabulary based on term co-occurrence and agglomerates highly overlapping inter-partition cells to produce the mined topics. While alternative approaches define a topic as a probabilistic distribution over the complete vocabulary, SWMH topics are subsets of such vocabulary. Interestingly, the topics mined by SWMH underlie themes from the corpus at different levels of granularity. We extensively evaluate the meaningfulness of the mined topics both qualitatively and quantitatively on the NIPS (1.7K documents), 20 Newsgroup (20K), Reuters (800K) and Wikipedia (4M) corpora.
AOC 09/02/2016 Primal Heuristics for Branch-and-Price , par Francois Vanderbeck
Francois Vanderbeck, Institute of Mathematics (IMB), University of Bordeaux  
Salle B107, bâtiment B, Université de Villetaneuse
09/02/2016    12:30 - 13:30
Résumé :
Math heuristics have become an essential component in mixed integer programming (MIP) solvers. Extending generic MIP heuristics, our study outlines generic procedures to build primal solutions in the context of a Branch-and-Price approach and reports on their performance. Rounding the linear relaxation solution of the Dantzig-Wolfe reformu-lation, which is typically tighter than that of the original compact formulation, sometimes produces better solutions than state-of-the-art specialised heuristics as revealed by our numerical experiments. We focus on the so-called diving methods and their combination with diversification-intensification paradigms such as Limited Discrepancy Search, sub-MIPing, relaxation induced neighbourhood search, local branching, and strong branching. The dynamic generation of variables inherent to a column generation approach requires specific adaptation of heuristic paradigms. Our contribution lies in proposing simple strategies to get around these technical issues. Our numerical results on Generalized Assignment, Cutting Stock, and Vertex Coloring problems sets new benchmarks, highlighting the performance of diving heuristics as generic procedures in a column generation context.
AOC 02/02/2016 A Tabu Search Heuristic for a Staff Scheduling Problem, par Stefania Pan
Stefania Pan  
Salle B107, bâtiment B, Université de Villetaneuse
02/02/2016    12:30 - 13:30
Résumé :
Scheduling problems form a very large class of optimization problems en- countered in several industries and organizations of widely different kinds. The particular problem that we consider is a staff scheduling problem, which con- sists of assigning activities to employees by taking into account workload re- quirements and different other constraints (for instance legal, economic, or- ganizational and social constraints). Staff scheduling problems are NP-hard, heuristics methods are often used to deal with large scale practical problems. We focus on constraints which impose minimum and maximum duration on activities. These constraints make the problem difficult to solve. We propose a Tabu Search (TS) approach to deal with the specific staff scheduling problem taking into account workload requirements and activities duration constraints. Computational results show the effectiveness of the proposed approach compar- ing CPLEX solver.
A3 28/01/2016 Non negative matrix factorization for transfer learning, par Ievgen Redko
Ievgen Redko, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
28/01/2016    12:15 - 13:30
Résumé :
The ability of a human being to extrapolate previously gained knowledge to other domains inspired a new family of methods in machine learning called transfer learning. Transfer learning is often based on the assumption that objects in both target and source domains share some common feature and/or data space. If this assumption is false, most of transfer learning algorithms are likely to fail. In this work, we propose to investigate the problem of transfer learning from both theoretical and applicational points of view. First, we introduce a theoretical framework based on the Hilbert-Schmidt embeddings that allows us to improve the current state-of-the-art theoretical results on transfer learning by introducing a natural and intuitive distance measure with strong computational guarantees for its estimation. The proposed results combine the tightness of data-dependent bounds derived from Rademacher learning theory while ensuring the efficient estimation of its key factors. We also present two different methods to solve the problem of unsupervised transfer learning based on Non-negative matrix factorization techniques. First one represents a linear approach that aims at discovering an embedding for two tasks that decreases the distance between the corresponding probability distributions while preserving the non-negativity property. Second one proceeds using an iterative optimization procedure that aims at aligning the kernel matrices calculated based on the data from two tasks.
AOC 12/01/2016 An Exact Semidefinite Programming Approach for the Max-Mean Dispersion Problem, par Michele Garraffa
Michele Garraffa  
Salle B107, bâtiment B, Université de Villetaneuse
12/01/2016    12:30 - 13:30
Résumé :
This work proposes an exact algorithm for the Max-Mean Dispersion Problem (Max-Mean DP), an NP-hard combinatorial optimization problem whose aim is to select the subset of a set such that the average distance between elements is maximized. The problem admits a natural non-convex quadratic fractional formulation from which a semidefinite programming (SDP) relaxation can be derived. In general, semidefinite relaxations have been successfully used to determine tight (but usually computationally expensive) lower/upper bounds for challenging NP-hard problems, such as the Quadratic Assignment Problem and the Quadratic Knapsack Problem. The semidefinite relaxation for the Max-Mean DP can be further tightened by means of a cutting plane algorithm which iteratively adds the most violated triangular inequalities. The proposed approach embeds the SDP relaxation and the cutting plane algorithm into a branch and bound framework to solve Max-Mean DP instances to optimality. To authors' knowledge, this is the first exact algorithm that has been proposed for this problem. Computational experiments show that the proposed method is able to solve to optimality in reasonable time instances with up 100 elements, while standard methods for fractional combinatorial optimization manage instances whose size is less then or equal to 75. The presented approach can be generalized to other combinatorial problems with a quadratic fractional objective and linear constraints.
A3 17/12/2015 Clustering collaboratif guidé par la diversité, par Jérémie Sublime
Jérémie Sublime, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
17/12/2015    12:15 - 13:45
Résumé :
Le clustering collaboratif est un domaine émergeant dont le but est de permettre à plusieurs algorithmes d'échanger leurs informations afin d'améliorer leurs performances sur les données respectives auxquelles ils ont accès. La collaboration se déroule généralement en deux étapes, avec les algorithmes travaillant dans un premier temps sur leurs données de façons individuelles, puis échangeant leurs informations dans un second temps. Ce type d'apprentissage possède de nombreuses applications : clustering multi-vue, clustering multi-échelle, multi-expert, ou multi-distribué, ou encore le transfert de connaissances. La méthode proposée ici permet de résoudre un des problèmes majeurs du clustering collaboratif, à savoir l'échange d'informations entre algorithmes de clustering très différents et qui n'ont pas initialement été pensés pour cet objectif. Notre méthode permet ainsi à des algorithmes de différentes familles de travailler ensemble, et donne également la possibilité de pondérer l'influence de certains d'entre eux avec des critères tels que la qualité ou la diversité de leurs solutions.
CALIN 15/12/2015 Sur la forme limite de l'identité dans le tas de sable abélien, par Andrea Sportiello
Andrea Sportiello  
Salle B107, bâtiment B, Université de Villetaneuse
15/12/2015    16:30 -
Résumé :
Le modèle du Tas de Sable Abélien décrit d'une façon élémentaire des processus de diffusion dans des réseaux. Des configurations de sable instables se stabilisent en des configurations stables, suite à une dynamique de avalanches. Malgré sa simplicité, ce modèle présente des phenoménes surprenents. On peut ansi considérer des configurations instables très simples à décrire, sur des réseaux réguliers, et observer le résultat à la fin de l'avalanche : on verra apparaitre des formes fractales complexes. Une de ces configurations est l'identité récurrente, Id. Quand le graphe est une portion carrée, de taille L, du réseau carré. On a donc une suite Id(L) de configurations, qui, mises à l'échelle, semblent converger vers une forme limite fractale, qui fascine les chercheurs depuis longtemps. On vient d'obtenir une description complète de cette forme. Ce résultat fait apparaitre plusieurs surprises: tous les points de contact entre les morceaux qui forment le fractal ont des coordonnées (x,y) qui appartiennent au meme corps cubique. Par exemple, le bien connu "carré bleu" qu'on trouve au milieu de la configuration est à une distance du bord de 0.58315637..., c'est à dire, la seule racine réelle de l'équation 2x^3+3x^2+x-2=0.
CALIN 15/12/2015 Gog, Magog et Schützenberger, par Philippe Biane
Philippe Biane  
Salle B107, bâtiment B, Université de Villetaneuse
15/12/2015    15:30 -
Résumé :
Les triangles Gog et Magog sont formés d'entiers positifs satisfaisant certaines inégalités. Ils apparaissent dans de nombreuses questions d'algèbre, de combinatoire, de théorie des représentations ou de physique statistique. Je parlerai d'une approche récente, reposant sur l'involution de Schützenberger, du problème de construire des bijections explicites entre ces objets.
CALIN 15/12/2015 Le CRT est la limite d'échelle de grandes dissections aléatoires, par Bénédicte Haas
Bénédicte Haas  
Salle B107, bâtiment B, Université de Villetaneuse
15/12/2015    14:15 -
Résumé :
Une dissection du polygone régulier à n côtés est la graphe formé par le polygone et certaines de ses diagonales, avec la règle que deux diagonales ne peuvent se croiser qu'aux sommets du polygone. On s'intéresse ici au comportement asymptotiquement d'une dissection uniformément distribuée dans l'ensemble des dissections du polygone à n côtés. Nous verrons que multipliée par n^(-1/2) cette dissection uniforme converge vers un multiple du CRT brownien. Ce résultat se généralise à des mesures attribuant des poids de Boltzmann aux degrés des faces des dissections, lorsque ces poids décroissent suffisamment vite. Il s'agit d'un travail en collaboration avec Nicolas Curien et Igor Kortchemski.
CALIN 15/12/2015 Polynômes symétriques et inégalités, par Bodo Lass
Bodo Lass  
Salle B107, bâtiment B, Université de Villetaneuse
15/12/2015    11:45 -
Résumé :
Un théorème fondamental pour la théorie des égalités affirme que les polynômes symétriques élémentaires engendrent la sous-algèbre des polynômes symétriques, et sont algébriquement indépendants. Nous explorons l'utilité de ce résultat pour la théorie des inégalités.
RCLN 15/12/2015 The hard life of an opinion mining tool: dealing with deceptive opinions and irony., par Paolo Rosso
Paolo Rosso, Universidad Politécnica de Valencia, Espagne  
Salle B107, bâtiment B, Université de Villetaneuse
15/12/2015    11:00 - 12:00
Résumé :
With the increasing of social media, consumers rely more than ever on online reviews to make their decisions. A recent survey found that 87% of them have reinforced their decisions to purchase a product due to positive online reviews. At the same time 80% of consumers have changed their minds on the basis of negative information they found online. Therefore, online opinions play an important role for companies and there is an increasing trend to post fake reviews with the aim to sound authentic and deceive the consumers. The detection of deceptive opinions is a quite challenging problem and not only automatically (only 60% of humans discriminate between truthful and deceptive opinions with a certain degree of accuracy). In the first part of the talk I will give an overview of the state-of-thye-art approaches for detecting deceptive opinions. The second part of the talk is devoted to another issue that makes the life of a sentiment analysis tool quite difficult: detecting irony. In ironic opinions what is literally said is usually negated, and in absence of an explicit negation marker. This makes sentiment analysis quite challenging. Therefore, there is a growing interest from the research community in investigating the impact of irony on sentiment analysis and a task has been organized recently at SemEval in 2015 on sentiment analysis of figurative language in Twitter. In the talk I will describe how irony is employed in tweets and reviews and what are the recent state-of-the-art attempts for its automatic detection. Linguistic devices such as ambiguity, incongruity, unexpectedness and emotional contexts play an important role as triggers of irony. At the end I will also address the even more challenging fine-grained problem of discriminating between irony and sarcasm: e.g. If you find it hard to laugh at yourself, I would be happy to do it for you.
CALIN 15/12/2015 Approximants de Padé et polyzêtas, par Tanguy Rivoal
Tanguy Rivoal  
Salle B107, bâtiment B, Université de Villetaneuse
15/12/2015    10:45 -
Résumé :
Peu de résultats sont connus sur la nature diophantienne des valeurs de la fonction zêta et de leurs généralisations, les polyzêtas. Une méthode générale pour parvenir à montrer l'irrationalité de tel ou tel nombre consiste à construire des approximations polynomiales, dites de Padé, de séries entières, puis à spécialiser pour obtenir des approximations numériques de ces nombres. Je présenterai diverses constructions d'approximants de Padé dans le contexte des polyzêtas. Certaines proviennent de travaux en commun avec Stéphane Fischler.
CALIN 15/12/2015 Un théorème de factorisation pour le nombre des pavages en losanges d'un hexagone avec des trous triangulaires, par Christian Krattenthaler
Christian Krattenthaler  
Salle B107, bâtiment B, Université de Villetaneuse
15/12/2015    10:00 -
Résumé :
Je présenterai un curieux théorème de factorisation pour le nombre des pavages en losanges d'un hexagone avec symétrie verticale et horizontale dont plusieurs trous triangulaires ont été enlevés le long de l'axe de symétrie horizontale. Je relierai ce théorème avec des autres théorèmes de factorisation, et je discuterai quelques conséquences et questions ouvertes. Ce travail a été effectué en commun avec Mihai Ciucu.

"A factorisation theorem for the number of rhombus tilings of a hexagon with trianglar holes"

I shall present a curious factorisation theorem for the number of rhombus tilings of a hexagon with vertical and horizontal symmetry axis, with triangular holes along the latter axis. I shall set this theorem in relation with other factorisation theorems, and discuss some consequences and open questions. This is joint work with Mihai Ciucu.

CALIN 15/12/2015 Un théorème de factorisation pour le nombre des pavages en losanges d'un hexagone avec des trous triangulaires, par Christian Krattenthaler
Christian Krattenthaler  
Salle B107, bâtiment B, Université de Villetaneuse
15/12/2015    09:30 -
Résumé :
Je présenterai un curieux théorème de factorisation pour le nombre des pavages en losanges d'un hexagone avec symétrie verticale et horizontale dont plusieurs trous triangulaires ont été enlevés le long de l'axe de symétrie horizontale. Je relierai ce théorème avec des autres théorèmes de factorisation, et je discuterai quelques conséquences et questions ouvertes. Ce travail a été effectué en commun avec Mihai Ciucu.

"A factorisation theorem for the number of rhombus tilings of a hexagon with trianglar holes"

I shall present a curious factorisation theorem for the number of rhombus tilings of a hexagon with vertical and horizontal symmetry axis, with triangular holes along the latter axis. I shall set this theorem in relation with other factorisation theorems, and discuss some consequences and open questions. This is joint work with Mihai Ciucu.

CALIN 08/12/2015 Colored triangulations of arbitrary dimensions are stuffed Walsh maps, par Luca Lionni
Luca Lionni  
Salle B107, bâtiment B, Université de Villetaneuse
08/12/2015    14:00 -
Document attaché
Résumé :
Regular D-edge-colored graphs encode D-dimensional colored triangulations of pseudo-manifolds. We study such families of edge-colored graphs built from a finite but arbitrary set of building blocks, which extend the notion of p-angulations to arbitrary dimensions. I will introduce a bijection between any such family and some colored combinatorial maps which we call stuffed Walsh maps. Those maps generalize Walsh's representation of hypermaps as bipartite maps, by replacing the vertices which correspond to hyperedges with non-properly-edge-colored maps.

We are interested in the number of bi-chromatic cycles of the initial edge-colored graphs because because they encode the curvature of the corresponding triangulated pseudo-manifold. I will therefore present new tools that use the bijection in order to study the graphs which maximize the number of bi-chromatic cycles at fixed number of vertices and provide examples where the corresponding stuffed Walsh maps can be completely characterized.

CALIN 03/12/2015 Long-range order in random 3-colorings of Z^d [10h-12h], par Yinon Spinka
Yinon Spinka  
Salle B107, bâtiment B, Université de Villetaneuse
03/12/2015    14:00 -
Résumé :
Consider a random coloring of a bounded domain in Zd with the probability of each coloring F proportional to exp(-?*N(F)), where ?>0 is a parameter (representing the inverse temperature) and N(F) is the number of nea rest neighboring pairs colored by the same color. This is the anti-ferromagnetic 3-state Potts model of statistical physics, used to describe magnetic interactions in a spin system. The Kotecký conjecture is that in such a model, for d?3 and high enough ?, a sampled coloring will typically exhibit long-range order, placing the same color at most of either the even or odd vertices of the domain. We give the first rigorous proof of this fact for large d. This extends previous works of Peled and of Galvin, Kahn, Randall and Sorkin, who treated the case ?=infinity. No background in statistical physics will be assumed and all terms will be explained thoroughly. Joint work with Ohad Feldheim.
A3 03/12/2015 Distributed nearest neighbour mean shift clustering , par Tarn Duong
Tarn Duong, Post-doc A3  
Salle B107, bâtiment B, Université de Villetaneuse
03/12/2015    12:15 - 13:45
Résumé :
Data clustering is an important tool for extracting meaningful information from large data sets. Despite the popularity of k-means clustering, it possesses two important limitations as it (a) requires a prior choice of the number of clusters and (b) produces only ellipsoidal clusters. Mean shift clustering is a generalisation of k-means which overcomes these limitations by defining clusters via a gradient ascent search of the data density. Nearest neighbour approaches are well-suited to computing the gradient ascent for multivariate data as they adapt to the local data density. On the other hand, the data adaptivity of nearest neighbour mean shift (NNMS) involves a higher computational burden, in terms of execution time and memory than k-means, which has hindered the more widespread use of NN MS. Its computational burden can be reduced with approximate nearest neighbours via random scalar projections (Locality Sensitive Hashing, LSH). To illustrate the feasibility of Big Data Clustering beyond k-means, we implement NNMS-LSH on a distributed Spark Scala ecosystem for multivariate clustering and image segmentation.
CALIN 03/12/2015 Long-range order in random 3-colorings of Z^d [10h-12h], par Yinon Spinka
Yinon Spinka  
Salle B107, bâtiment B, Université de Villetaneuse
03/12/2015    10:00 -
Résumé :
Consider a random coloring of a bounded domain in Zd with the probability of each coloring F proportional to exp(-?*N(F)), where ?>0 is a parameter (representing the inverse temperature) and N(F) is the number of nea rest neighboring pairs colored by the same color. This is the anti-ferromagnetic 3-state Potts model of statistical physics, used to describe magnetic interactions in a spin system. The Kotecký conjecture is that in such a model, for d?3 and high enough ?, a sampled coloring will typically exhibit long-range order, placing the same color at most of either the even or odd vertices of the domain. We give the first rigorous proof of this fact for large d. This extends previous works of Peled and of Galvin, Kahn, Randall and Sorkin, who treated the case ?=infinity. No background in statistical physics will be assumed and all terms will be explained thoroughly. Joint work with Ohad Feldheim.
CALIN 02/12/2015 An overview of an analytic approach for branching processes (Colloquium : Les mercredis du LIPN), par Mark Ward
Mark Ward  
Salle B107, bâtiment B, Université de Villetaneuse
02/12/2015    15:00 -
Résumé :
One approach to solving some questions in probability theory--especially questions about asymptotic properties of algorithms and data structures--is to take an analytic approach, i.e., to utilize complex-valued methods of attack. These methods are especially useful with several types of branching processes, leader election algorithms, pattern matching in trees, data compression, etc. This talk will focus on some of the highlights of this approach. I endeavor to keep it at a level that is accessible for graduate students.
MERCRED 02/12/2015 An Overview of an Analytic Approach for Branching Processes, par Mark Ward
Mark Ward, Purdue University  
Salle B107, bâtiment B, Université de Villetaneuse
02/12/2015    14:00 - 15:00
Résumé :
One approach to solving some questions in probability theory--especially questions about asymptotic properties of algorithms and data structures--is to take an analytic approach, i.e., to utilize complex-valued methods of attack. These methods are especially useful with several types of branching processes, leader election algorithms, pattern matching in trees, data compression, etc. This talk will focus on some of the highlights of this approach. I endeavor to keep it at a level that is accessible for graduate students.
CALIN 02/12/2015 An overview of an analytic approach for branching processes (Colloquium : Les mercredis du LIPN), par Mark Ward
Mark Ward  
Salle B107, bâtiment B, Université de Villetaneuse
02/12/2015    14:00 -
Résumé :
One approach to solving some questions in probability theory--especially questions about asymptotic properties of algorithms and data structures--is to take an analytic approach, i.e., to utilize complex-valued methods of attack. These methods are especially useful with several types of branching processes, leader election algorithms, pattern matching in trees, data compression, etc. This talk will focus on some of the highlights of this approach. I endeavor to keep it at a level that is accessible for graduate students.
MERCRED 18/11/2015 Coin-tossing in algorithmics, par Hsien-Kuei Hwang
Hsien-Kuei Hwang, Academia sinica  
Salle B107, bâtiment B, Université de Villetaneuse
18/11/2015    15:00 - 16:00
Résumé :
Coin-tossing is one of the simplest ways of resolving a conflict, deciding between two alternatives, and generating random phenomena. It has been widely adopted in many daily-life situations and scientific disciplines. In this talk, I will present a few research themes connected to the use of coin-tossing in algorithmics, taken from my research: these include random permutations, data structures, evolutionary algorithms and leader selection. The main focus will be on the stochastic behaviors and the methods of analysis.
CALIN 18/11/2015 Coin Tossing in algorithmics (Colloquium : Les mercredis du LIPN), par Hsien-Kuei Hwang
Hsien-Kuei Hwang  
Salle B107, bâtiment B, Université de Villetaneuse
18/11/2015    15:00 -
Résumé :
Coin-tossing is one of the simplest ways of resolving a conflict, deciding between two alternatives, and generating random phenomena. It has been widely adopted in many daily-life situations and scientific disciplines. In this talk, I will present a few research themes connected to the use of coin-tossing in algorithmics, taken from my research: these include random permutations, data structures, evolutionary algorithms and leader selection. The main focus will be on the stochastic behaviors and the methods of analysis.
CALIN 17/11/2015 A computer-algebra-based formal proof of the irrationality of ?(3), par Frédéric Chyzak
Frédéric Chyzak  
Salle B107, bâtiment B, Université de Villetaneuse
17/11/2015    14:00 -
Document attaché
Résumé :
We report on the formal verification of an irrationality proof of the evaluation at 3 of the Riemann zeta function. This verification uses the Coq proof assistant in conjunction with algorithmic calculations in Maple. This irrationality result was first proved by Apéry in 1978, and our formalization follows the proof path of his original presentation. The crux of it is to establish that some sequences satisfy a common recurrence. We formally prove this by an a posteriori verification of calculations performed by a Maple session. This bases on computer-algebra algorithms implementing Zeilberger's approach of creative telescoping. This experience illustrates the limits of the belief that creative telescoping can discover recurrences for holonomic sequences that are easily checked a posteriori. We discuss this observation and describe the protocol we devised in order to produce complete formal proofs of the recurrences. Beside establishing the recurrences, our proof combines the formalization of arithmetical ingredients and of some asymptotic analysis.
Joint work with Assia Mahboubi, Thomas Sibut-Pinote, and Enrico Tassi.
AOC 17/11/2015 Identités de Gallai chromatiques opérant sur la fonction Theta Lovasz, par Denis Cornaz
Denis Cornaz, Lamsade  
Salle B107, bâtiment B, Université de Villetaneuse
17/11/2015    12:30 - 13:30
Résumé :
Un paramètre de graphe (une fonction qui associe un entier à tout graphe) est dit sandwich si, pour tout graphe, il est compris entre la taille de la clique maximum et le nombre chromatique. Nous définissons à l'aide d'un graphe auxiliaire (un sous-graphe partiel du line-graphe) un opérateur PHI qui transforme tout paramètre sandwich en un autre paramètre sandwich. Nous montrons que PHI améliore la qualité des bornes polynomiales pour la coloration (bornes obtenues par la programmation semie-définie), de plus, expérimentalement, l'amélioration est significative. Par ailleurs, PHI détériore la qualité de la borne obtenue par la programmation linéaire.
CALIN 20/10/2015 Forme limite de tableaux de Young rectangulaires, par Philippe Marchal
Philippe Marchal  
Salle B107, bâtiment B, Université de Villetaneuse
20/10/2015    14:00 -
Résumé :
En 2004, Pittel et Romik ont montré l'existence d'une forme limite pour les tableaux de Young rectangulaires. Je montrerai comment la méthode probabiliste des "densités", que je développe depuis quelques travaux déjà, permet de retrouver cette forme limite et donne aussi les fluctuations sur le bord : on trouve une gaussienne dans les coins et Tracy-Widom ailleurs sur le bord.
RCLN 19/10/2015 An uncertainty approach (probabilistic + possibilistic) for analyzing users' attitudes (emotions & opinions (feelings & judgments)) from their literature, par Sayyed Ali Hossayni
Sayyed Ali Hossayni  
Salle B107, bâtiment B, Université de Villetaneuse
19/10/2015    14:00 - 15:00
Résumé :
In this seminar, we adopt an uncertainty approach to attitude prediction. Uncertainty approach includes probabilistic and possibilistic approaches and attitude includes opinion and emotion. The seminar has two parts: probabilistic & possibilistic attitude mining. In the probabilistic part, we first propose a new approach to attitude mining and prove its efficiency by applying it on collaborative filtering. Our approach, unlike the existing ones in state of the art, does not represent the usersÂ’ attitudes as numbers, but as a probability/possibility distribution function (PDF) (mathematically speaking, not a whole graph but its few (normally 1 or 2) parameter(s)). Then, we suggest upgrading Sentilo (the existing opinion mining platform in state of the art) to become able to provide more knowledge about attitude of the usersÂ’ (or attitude of whom they wrote about) about the entities/topics. In the second part of the seminar, we explain a different type of uncertainty (possibility) and also its better impact (under some circumstances) on data mining. Then, we will propose application of a new possibilistic tools that we customize it for text mining for being utilizable in attitude prediction. It is notable that the second part of the presentation can also be useful for general data mining purposes.
CALIN 13/10/2015 Analyse asymptotique et génération aléatoire des structures en diamant, par Olivier Bodini
Olivier Bodini  
Salle B107, bâtiment B, Université de Villetaneuse
13/10/2015    14:00 -
Résumé :
Nous allons d'écrire et étudier une classe importante de DAG, appelé structure en diamant. Cette étude repose sur une analyse asymptotique d'équations différentielles non linéaires. Nous expliquerons aussi comment développer des générateurs aléatoires efficaces pour ces structures. Travail en commun avec Hsien-Kuei Hwang, Antoine Genetrini et Xavier Fontaine.
CALIN 09/10/2015 Tenseurs aléatoires (soutenance de thèse), par Stéphane Dartois
Stéphane Dartois  
Salle B107, bâtiment B, Université de Villetaneuse
09/10/2015    12:45 -
Résumé :
During this defense I present pieces of the work I achieved on random tensor models (tensor models for short). I will define colored triangulations and then review their combinatorics. After this is done I show how one can write integral representation of their generating series. These representations are called tensor models. Using this representation I will describe the combinatorial 1/N expansion for two different kinds of models generating specific classes of colored and non-colored combinatorial maps. I will then concentrate on a specific model, that is the simpler non trivial tensor model and explore some of its properties. In particula r I review the properties of its double scaling limit, then using its Hubbard-Stratanovitch representation, I show how one can use matrix models techniques to recover results obtained using combinatorial techniques. I will finally present several results that point towards integrable structures in the framework of random tensor models.
A3 08/10/2015 Amélioration de l'apprentissage de forêts d'arbres latents : quelle mesure pour évaluer la qualité de clustering ? Application en bioinformatique. , par Christine Sinoquet
Christine Sinoquet, LINA, Nantes  
Salle B107, bâtiment B, Université de Villetaneuse
08/10/2015    12:15 - 13:30
Résumé :
Au carrefour entre théorie des graphes et théorie des probabilités, nous avons proposé une nouvelle classe de modèles graphiques probabilistes [1]. Ce type de modèle, ou forêt de modèles hiérarchiques à variables latentes (FLTM - Forest of latent tree models) [2], est dédié à la modélisation de données complexes, de grande dimension, et fortement corrélées. Le choix d'une modélisation hiérarchique a facilité la conception d'un algorithme d'apprentissage du modèle qui passe à l'échelle. L'algorithme d'apprentissage du modèle FLTM repose sur un processus de clustering ascendant hiérarchique. Parmi un ensemble de méthodes de clustering compatibles avec la très grande dimension des données modélisées, le problème est d'identifier la meilleure méthode de clustering et le meilleur paramétrage pour cette dernière. En préambule, les principes de l'évaluation extrinsèque et de l'évaluation intrinsèque de clustering seront rappelés. Les résultats d'une première étude focalisée sur la comparaison des comportements de quatre critères intrinsèques seront ensuite exposés [3]. Des partitions indépendantes, générées aléatoirement, selon divers protocoles, ont d'abord été comparées. Trois méthodes de clustering ont été considérées. Des couples de partitions (prédite, réelle) ont ensuite été comparées pour ces quatre critères extrinsèques, sur données génétiques. Cependant, la connaissance de la partition réelle n'étant elle-même qu'approchée, une utilisation réaliste doit recourir à un critère intrinsèque. Le choix s'est porté sur deux d'entre eux : le critère de redondance et la différence d'entropies normalisée, spécialement adaptée aux données génétiques. Pour chacune des trois méthodes de clustering utilisées, une deuxième étude s'est donc attachée à comparer les distributions des valeurs de ces deux critères, obtenues pour différents ajustements des paramètres de la méthode de clustering. Les résultats de cette étude seront présentés. Dans le cas de données génétiques, bien qu'approchée, la connaissance de la partition réelle révèle certaines caractéristiques de la distribution des tailles de clusters. Une troisième étude s'est donc focalisée sur l'amélioration du critère de la différence d'entropies normalisée, afin de prendre en compte ces caractéristiques. Quatre versions de ce critère sont comparées, pour des données génétiques. Enfin, ces études seront replacées dans le contexte plus vaste d'une campagne de tests intensifs visant la comparaison de trois méthodes alternatives aux GWAS classiques. L'objectif d'une GWAS (genome-wide association study - étude d'association à l'échelle du génome) est d'identifier les facteurs génétiques potentiellement responsables d'un phénotype (e.g. une pathologie génétique). Dans le contexte du projet ANR SAMOGWAS (Specific Advanced MOdels for Genome Wide Association Studies), trois stratégies GWAS sont comparées : l'une exploitant le modèle FLTM [3], l'une utilisant une variante des forêts aléatoires, la troisième combinant les deux approches précédentes. Des résultats préliminaires seront présentés. [1] R. Mourad, C. Sinoquet and P. Leray (2011) A hierarchical Bayesian network approach for linkage disequilibrium modeling and data-dimensionality reduction prior to genome-wide association studies. BMC Bioinformatics, 12(1), 16, doi:10.1186/1471-2105-12-16. [2] R. Mourad, C. Sinoquet, N. L. Zhang, T. Liu and P. Leray (2013) A survey on latent tree models and applications. Journal of Artificial Intelligence Research, 47, 157-203. [3] D.-T. Phan, P. Leray and C. Sinoquet (2015) Latent Forests to Model Genetical Data for the Purpose of Multilocus Genome-wide Association Studies. Which clustering should be chosen? To appear in BIOSTEC2015, Communication in Computer and Information Science, Springer.
CALIN 06/10/2015 Calculabilité et pavages, par Pascal Vanier
Pascal Vanier  
Salle B107, bâtiment B, Université de Villetaneuse
06/10/2015    14:00 -
Résumé :
Les pavages, ou sous-shifts de type fini sont des ensembles de coloriages du plan vérifiant des contraintes locales en nombre fini. Nous nous intéresserons en particulier au problèmes d'isomorphisme entre sous-shifts, connu sous le nom de conjugaison et plus particulièrement aux invariants de conjugaison, qui sont des "objets" permettant de caractériser certains aspects des sous-shifts. Nous donnerons en particulier des caractérisations calculatoires de ces derniers qui permettront de voir les liens intimes qui lient pavages et classes de complexité/calculabilité.
AOC 06/10/2015 The Johnson-Lindenstrauss Lemma in Linear and Integer Feasibility, par Leo Liberti
Leo Liberti, LIX, Ecole Polytechnique  
Salle B107, bâtiment B, Université de Villetaneuse
06/10/2015    12:30 - 13:30
Résumé :
The Johnson-Lindenstrauss lemma allows dimension reduction on real vectors with low distortion on their pairwise Euclidean distances. This result is often used in algorithms such as $k$-means or $k$ nearest neighbours since they only use Euclidean distances, and has sometimes been used in optimization algorithms involving the minimization of Euclidean distances. In this paper we introduce a first attempt at using this lemma in the context of feasibility problems in linear and integer programming, which cannot be expressed only in function of Euclidean distances. Leo Liberti, Vu Khac Ky, Pierre-Louis Poirion CNRS LIX, Ecole Polytechnique, Palaiseau, France
A3 01/10/2015 Clustering sous contraintes en Programmation par Contraintes, par Christel Vrain
Christel Vrain, LIFO, Orléans  
Salle B107, bâtiment B, Université de Villetaneuse
01/10/2015    12:15 - 13:30
Résumé :
La classification non supervisée sous contraintes (aussi appelée clustering sous contraintes) est une tâche importante de fouille de données, permettant de modéliser plus finement une tâche de clustering en intégrant des contraintes utilisateur. Divers types de contraintes peuvent être considérés ; les contraintes les plus courantes sont les contraintes must-link (ML) ou cannot-link (CL) spécifiant que des paires d’objets doivent être (respectivement, ne doivent pas être) dans le même cluster. D’autres contraintes peuvent aussi être posées sur les clusters, précisant par exemple, une borne sur leur diamètre ou sur leur taille. Néanmoins, concevoir un algorithme capable de traiter différents types de contraintes est difficile et la plupart des approches tendent à étendre les méthodes classiques de clustering en intégrant un unique type de contraintes. Plusieurs travaux ont montré l’intérêt de la Programmation par Contraintes (PPC) pour la fouille de données. Modéliser en PPC a deux avantages : la déclarativité qui permet d’ajouter facilement de nouvelles contraintes, la capacité à énumérer toutes les solutions satisfaisant les contraintes et la capacité, dans le cas de l’optimisation d’un critère, à trouver une solution optimale satisfaisant toutes les contraintes (s’il en existe une). Dans cet exposé, nous ne considérons que l’apprentissage de partitions et nous donnons deux exemples de l’utilisation de la Programmation par Contraintes pour le clustering sous contraintes. Le premier exemple, proposé par [T. Guns, S. Nijssen, .L De Raedt] modélise le clustering conceptuel : les données sont décrites par leurs propriétés et à chaque cluster est associé un motif, i.e, un ensemble de propriétés que toutes les données du cluster satisfont. Dans le second exemple, issu de nos travaux [T.B. H. Dao, K.C. Duong, C. Vrain], un cadre déclaratif et générique permet de modéliser différentes tâches de clustering sous contraintes, étant donnée une mesure de dissimilarité entre les objets.
RCLN 28/09/2015 Golfred: Génération de récits à partir d'expériences spatiales d'un robot de service par extraction de connaissances textuelles, par Jorge Garcia Flores
Jorge Garcia Flores, LIPN  
Salle B107, bâtiment B, Université de Villetaneuse
28/09/2015    14:00 - 15:00
Résumé :
Le but du projet est de donner à un robot la capacité de lire les phrases écrites qu'il rencontre sur son chemin et d'en faire un compte rendu à la fin de son parcours. Notre hypothèse est que la production de ce genre de récits est possible en embarquant le système de lecture automatique (machine reading) FRED dans le robot Golem (développé par l'équipe de Luis A. Pineda, professeur à l'IIMAS) et en adaptant le système de génération de texte RTGen (développé par l'équipe de Claire Gardent au LORIA). Le robot a la capacité de se déplacer dans le labo et de reconnaître les messages textuels, tandis que FRED est capable de chercher et d'interpréter des mots clés à partir de DBPedia, la base de données de Wikipedia. Enfin l'adaptation de RTgen aux données RDF de DBPedia permettra de transformer le graphe RDF construits par FRED en un texte décrivant le parcours de Golem. Le principal critère discursif pour la génération du récit est le parcours spatial: Golem (aidé par FRED et RTGen) raconte ce qu'il a lu sur son chemin (et trouvé sur Wikipedia).
MERCRED 23/09/2015 A fresh view on the matching problem, par Sergio Caracciolo
Sergio Caracciolo, Univ. Milano  
Salle B107, bâtiment B, Université de Villetaneuse
23/09/2015    14:00 - 16:00
Résumé :
I will review some new results in the stochastic euclidean bipartite matching problem. First I will look at the simple one dimensional version, for which many exact results can be achieved. Afterwards, by discarding the discrete nature of the problem, as usual in a critical system, I will show how it is possible to resort to a continuous version for which an analytical expression for the minimum cost and correlation functions can be computed.
CALIN 23/09/2015 A fresh view on the matching problem (attention, c'est un mercredi), par Sergio Caracciolo
Sergio Caracciolo  
Salle B107, bâtiment B, Université de Villetaneuse
23/09/2015    14:00 -
Résumé :
I will review some new results in the stochastic euclidean bipartite matching problem. First I will look at the simple one dimensional version, for which many exact results can be achieved. Afterwards, by discarding the discrete nature of the problem, as usual in a critical system, I will show how it is possible to resort to a continuous version for which an analytical expression for the minimum cost and correlation functions can be computed.
AOC 15/09/2015 A branch-and-cut-and-price algorithm for the green vehicle routing problem with partial recharges and multiple technologies, par Alberto Ceselli
Alberto Ceselli  
Salle B107, bâtiment B, Université de Villetaneuse
15/09/2015    12:30 - 13:30
Résumé :
Abstract: We tackle a variation of the vehicle routing problem in which the transportation fleet is composed of electric vehicles with limited autonomy in need for recharge during the execution of their duties. Different technologies can be chosen at each station, offering different trade-off between recharge cost and time. We present an algorithm exploiting column generation, cutting planes and branch-and-bound for the exact solution of the problem. The pricing phase requires elementary resource constrained shortest path problems to be solved, and is carried out with both heuristics and an exact dynamic programming routine. The cut separation phase is performed by running heuristics from the literature on a particular support graph. Experiments on benchmark instances from the VRP literature reveal that our algorithm is effective in solving instances with up to thirty customers, nine recharge stations, five vehicles and three technologies to optimality.
CALIN 08/09/2015 Why and when does the half-normal distribution appear in combinatorics?, par Michael Wallner
Michael Wallner  
Salle B107, bâtiment B, Université de Villetaneuse
08/09/2015    14:00 -
Résumé :
We present an extension of a theorem by Michael Drmota and Michèle Soria [1997] that can be used to identify the limiting distribution for a class of combinatorial schemata. This is achieved by determining analytical and algebraic properties of the associated bivariate generating function. We give sufficient conditions implying a half-normal limiting distribution, extending the known conditions leading to either a Rayleigh, a Gaussian or a convolution of the last two distributions. Finally, we present some applications to lattice path and tree enumeration, images and preimages in random mappings.
AOC 02/07/2015 Solving the quadratic shortest path problem , par Borzou Rostami
Borzou Rostami, Université de Dortmund  
Salle B107, bâtiment B, Université de Villetaneuse
02/07/2015    12:30 - 13:30
Résumé :
Finding the shortest path in a directed graph is one of the most important combinatorial optimization problems, having applications in a wide range of fields. In its basic version, however, the problem fails to represent situations in which the value of the objective function is determined not only by the choice of each single arc, but also by the combined presence of pairs of arcs in the solution. In this paper we model these situations as a Quadratic Shortest Path Problem, which calls for the minimization of a quadratic objective function subject to shortest-path constraints. We prove strong NP-hardness of the problem and analyze polynomially solvable special cases, obtained by restricting the distance of arc pairs in the graph that appear jointly in a quadratic monomial of the objective function. Based on this special case and problem structure, we devise fast lower bounding procedures for the general problem and show computationally that they clearly outperform other approaches proposed in the literature in terms of their strength.
RCLN 29/06/2015 Annotation et exploration de textes de spécialité - fragments d'une expérience, par François Lévy, Sylvie Szulman
François Lévy, Sylvie Szulman, LIPN/RCLN  
Salle B107, bâtiment B, Université de Villetaneuse
29/06/2015    14:00 - 15:00
Résumé :
Nous avons (ré)écrit un outil de manipulation conjointe d'annotations et de textes annotés, Omtat (One More Textual Annotation Tool) qui permet de visualiser les annotations et d'en ajouter, Les annotations, inspirées de Brat (Brat rapid annotation tool) peuvent porter sur une zone discontinue et qualifier des annotations-arguments. Un moteur de requêtes permet d'extraire et d'exploiter des ensembles de documents, phrases et annotations. Les premiers tests portent sur des textes de biologies et sur des textes juridiques, pour lesquels nous avons créé quelques types d'annotations spécialisées. Nous en profiterons pour dire en quoi spécialiser les annotations en tenant compte du domaine nous parait utile et tenter de convaincre que les résultats peuvent être intéressants.