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Total Positivity and Two Inequalities by Athanasiadis and Tzanaki

  • Lili Mu,
  • Volkmar Welker

摘要

Let \(\Delta \) Δ be a \((d-1)\) ( d - 1 ) -dimensional simplicial complex and \(h^ \Delta = (h_0^ \Delta ,\ldots , h_d^ \Delta )\) h Δ = ( h 0 Δ , , h d Δ ) its h-vector. For a face uniform subdivision operation \({\mathcal {F}}\) F , we write \(\Delta _{\mathcal {F}}\) Δ F for the subdivided complex and \(H_{\mathcal {F}}\) H F for the matrix, such that \(h^ {\Delta _{\mathcal {F}}} = H_{\mathcal {F}}h^ \Delta \) h Δ F = H F h Δ . In connection with the real rootedness of symmetric decompositions, Athanasiadis and Tzanaki studied for strictly positive h-vectors the inequalities \(\frac{h_0^ \Delta }{h_1^ \Delta } \le \frac{h_1^\Delta }{h_{d-1}^ \Delta } \le \cdots \le \frac{h_d^ \Delta }{h_0^\Delta }\) h 0 Δ h 1 Δ h 1 Δ h d - 1 Δ h d Δ h 0 Δ and \(\frac{h_1^\Delta }{h_{d-1}^\Delta } \ge \cdots \ge \frac{h_{d-2}^\Delta }{h_2^\Delta } \ge \frac{h_{d-1}^\Delta }{h_1^\Delta }\) h 1 Δ h d - 1 Δ h d - 2 Δ h 2 Δ h d - 1 Δ h 1 Δ . In this paper, we show that if the inequalities holds for a simplicial complex \(\Delta \) Δ and \(H_{\mathcal {F}}\) H F is \(\hbox {TP}_2\) TP 2 (all entries and two minors are non-negative), then the inequalities hold for \(\Delta _{\mathcal {F}}\) Δ F . We prove that if \({\mathcal {F}}\) F is the barycentric subdivision, then \(H_{\mathcal {F}}\) H F is \(\hbox {TP}_2\) TP 2 . If \({\mathcal {F}}\) F is the rth-edgewise subdivision, then work of Diaconis and Fulman shows \(H_{\mathcal {F}}\) H F is \(\hbox {TP}_2\) TP 2 . Indeed, in this case by work of Mao and Wang, \(H_{\mathcal {F}}\) H F is even TP.