Shelling and triangulating the (extra)ordinary polytope

Dual matroid polytopes and internal activity of independence complexes

Shelling orders are a ubiquitous tool used to understand invariants of cell complexes. Significant effort has been made to develop techniques to decide when a given complex is shellable. However, empirical evidence shows that some shelling orders are better than others. In this article, we explore this phenomenon in the case of matroid independence complexes. Based on a new relation between shellability of dual matroid polytopes and independence complexes, we outline a systematic way to investigate and compare different shellings orders. We explain how our new tools recast and deepen various c…

Alcoved 多胞体的 Ehrhart 级数

The Ehrhart series of alcoved polytopes

本文提出通过 alcove 的特定壳化顺序计算任意 alcoved 多胞体的 Ehrhart 级数的方法，并揭示了 Early 的装饰有序集合划分与超单纯形 $\Delta_{2,n}$ 壳化顺序之间的关联。

Valid Orderings of Real Hyperplane Arrangements

Given a real finite hyperplane arrangement A and a point p not on any of the hyperplanes, we define an arrangement vo(A,p), called the *valid order arrangement*, whose regions correspond to the different orders in which a line through p can cross the hyperplanes in A. If A is the set of affine spans of the facets of a convex polytope P and p lies in the interior of P, then the valid orderings with respect to p are just the line shellings of p where the shelling line contains p. When p is sufficiently generic, the intersection lattice of vo(A,p) is the *Dilworth truncation* of the semicone of A…

几何格中的线壳化

Line Shellings of Geometric Lattices

本文通过引入线壳化方法，证明了 matroid 平面格的顺序复形及所有嵌套集复形的壳化性。

Families of polytopal digraphs that do not satisfy the shelling property

A polytopal digraph $G(P)$ is an orientation of the skeleton of a convex polytope $P$. The possible non-degenerate pivot operations of the simplex method in solving a linear program over $P$ can be represented as a special polytopal digraph known as an LP digraph. Presently there is no general characterization of which polytopal digraphs are LP digraphs, although four necessary properties are known: acyclicity, unique sink orientation(USO), the Holt-Klee property and the shelling property. The shelling property was introduced by Avis and Moriyama (2009), where two examples are given in $d=4$ d…

The $h^*$-polynomial of the order polytope of the zig-zag poset

We describe a family of shellings for the canonical triangulation of the order polytope of the zig-zag poset. This gives a new combinatorial interpretation for the coefficients in the numerator of the Ehrhart series of this order polytopein terms of the swap statistic on alternating permutations.