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Discrete concavity and the half-plane property. (English) Zbl 1228.90091

The author introduces 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 \(M\)-concave functions studied in the literature. It is shown that the tropicalization of the space of polynomials with the half-plane property is strictly contained in the space of \(M\)-concave functions. Based on a result of Hardy and Hutchinson a short proof of Speyer’s “hive theorem” is given, which he had used to give a new proof of Horn’s conjecture on eigenvalues of sums of Hermitian matrices. Finally, it is shown that a natural extension of Speyer’s theorem to higher dimensions is false.

MSC:

90C27 Combinatorial optimization
30C15 Zeros of polynomials, rational functions, and other analytic functions of one complex variable (e.g., zeros of functions with bounded Dirichlet integral)
05B35 Combinatorial aspects of matroids and geometric lattices
15A42 Inequalities involving eigenvalues and eigenvectors