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arXiv · 1301.2449

Complete monotonicity for inverse powers of some combinatorially defined polynomials

Alexander D. Scott·Alan D. Sokal
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Abstract

We prove the complete monotonicity on $(0,\infty)^n$ for suitable inverse powers of the spanning-tree polynomials of graphs and, more generally, of the basis generating polynomials of certain classes of matroids. This generalizes a result of Szego and answers, among other things, a long-standing question of Lewy and Askey concerning the positivity of Taylor coefficients for certain rational functions. Our proofs are based on two_ab initio_ methods for proving that $P^{-\beta}$ is completely monotone on a convex cone $C$: the determinantal method and the quadratic-form method. These methods are closely connected with harmonic analysis on Euclidean Jordan algebras (or equivalently on symmetric cones). We furthermore have a variety of constructions that, given such polynomials, can create other ones with the same property: among these are algebraic analogues of the matroid operations of deletion, contraction, direct sum, parallel connection, series connection and 2-sum. The complete monotonicity of $P^{-\beta}$ for some $\beta > 0$ can be viewed as a strong quantitative version of the half-plane property (Hurwitz stability) for $P$, and is also related to the Rayleigh property for matroids.

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BibTeXRIS

Alexander D. Scott, Alan D. Sokal. 2013-01-11. Complete monotonicity for inverse powers of some combinatorially defined polynomials. https://doi.org/10.1007/s11511-014-0121-6

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