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.

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Dernière modification : Thursday 21 November 2024

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