arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1303.2302math.CO
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$B$型扰动多项式的对称单峰分解

A symmetric unimodal decomposition of the derangement polynomial of type $B$

Christos A. Athanasiadis, Christina Savvidou

摘要:

对称群的无序排列多项式$d_n (x)$通过超出数来枚举无序排列。超八面体群的无序多项式$d^B_n(x)$是自然型$B$的类似物。本文给出了该多项式的一个新的组合公式。这个公式意味着,$d^B_n (x)$分解为两个非负的,对称的和单峰多项式的对称中心相差一半,从而提供了一个新的透明证明其单峰。一个几何的解释,类似于斯坦利的解释$d_n (x)$的本地$h$ -多项式的重心重分的单纯形,给出了这种分解的被加数。这种解释导致一个单峰分解和一个新的公式的欧拉多项式类型$B$。这里介绍的各种分解多项式还研究了递归,生成函数,组合解释,扩展和真正的根。

英文摘要:

The derangement polynomial $d_n (x)$ for the symmetric group enumerates derangements by the number of excedances. The derangement polynomial $d^B_n(x)$ for the hyperoctahedral group is a natural type $B$ analogue. A new combinatorial formula for this polynomial is given in this paper. This formula implies that $d^B_n (x)$ decomposes as a sum of two nonnegative, symmetric and unimodal polynomials whose centers of symmetry differ by a half and thus provides a new transparent proof of its unimodality. A geometric interpretation, analogous to Stanley's interpretation of $d_n (x)$ as the local $h$-polynomial of the barycentric subdivision of the simplex, is given to one of the summands of this decomposition. This interpretation leads to a unimodal decomposition and a new formula for the Eulerian polynomial of type $B$. The various decomposing polynomials introduced here are also studied in terms of recurrences, generating functions, combinatorial interpretations, expansions and real-rootedness.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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