Discrete Concavity and the Half-Plane Property

  • Authors:
  • Petter Brändén

  • Affiliations:
  • pbranden@math.su.se

  • Venue:
  • SIAM Journal on Discrete Mathematics
  • Year:
  • 2010

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Abstract

Murota et al. have recently developed a theory of discrete convex analysis which concerns $M$-convex functions on jump systems. We introduce here a family of $M$-concave functions arising naturally from polynomials (over a field of generalized Puiseux series) with prescribed nonvanishing properties. This family contains several of the most well studied $M$-concave functions in the literature. In the language of tropical geometry, we study the tropicalization of the space of polynomials with the half-plane property and show that it is strictly contained in the space of $M$-concave functions. We also provide a short proof of Speyer's “hive theorem” which he used to give a new proof of Horn's conjecture on eigenvalues of sums of Hermitian matrices.