Total positivity and two inequalities by Athanasiadis and Tzanaki

Lili Mu, Volkmar Welker

Published 2024-04-04Version 1

Let $\Delta$ be a (d-1)-dimensional simplicial complex and h^\Delta = (h_0^ ,.. , h_d) its h-vector. For a face uniform subdivision operation \F we write \Delta_\F for the subdivided complex and H_\F for the matrix such that h^{\Delta_\F} = H_\F h^\Delta. In connection with the real rootedness of symmetric decompositions Athanasiadis and Tzanaki studied for strictly positive h-vectors the inequalities h_0 / h_1 \leq h_1 / h_{d-1} \leq .... \leq h_d / h_0 and h_1 / h_{d-1} \geq ... \geq h_{d-2} / h_2 \geq h_{d-1} / h_1. In this paper we show that if the inequalities holds for a simplicial complex $\Delta$ and H_\F is TP_2 (all entries and two minors are non-negative) then the inequalities hold for \Delta_\F. We prove that if \F is the barycentric subdivision then H_\F is TP_2. If \F is the rth-edgewise subdivision then work of Diaconis and Fulman shows H_\F is TP_2. Indeed in this case by work of Mao and Wang H_\F is even TP.