48 citations · 135 across the 26 of their papers we have counts for
27 papers
The toric g-vector of nestohedra
Richard Ehrenborg, Gábor Hetyei, Margaret Readdy
We show the entries of the toric g-vector of any dual simplicial polytope is a nonnegative integer linear combination of its gamma-vector entries. We give combinatorial interpretat…
Catalan-Spitzer permutations
Richard Ehrenborg, Gábor Hetyei, Margaret Readdy
We study two classes of permutations intimately related to the visual proof of Spitzer's lemma and Huq's generalization of the Chung-Feller theorem. Both classes of permutations ar…
Pizza and 2-structures
Richard Ehrenborg, Sophie Morel, Margaret Readdy
Let be a Coxeter hyperplane arrangement in -dimensional Euclidean space. Assume that the negative of the identity map belongs to the associated Coxeter group .…
Sharing pizza in n dimensions
Richard Ehrenborg, Sophie Morel, Margaret Readdy
We introduce and prove the -dimensional Pizza Theorem: Let be a hyperplane arrangement in . If is a measurable set of finite volume, the {pizza…
A generalization of combinatorial identities for stable discrete series constants
Richard Ehrenborg, Sophie Morel, Margaret Readdy
This article is concerned with the constants that appear in Harish-Chandra's character formula for stable discrete series of real reductive groups, although it does not require any…
Classification of uniform flag triangulations of the boundary of the full root polytope of type
Richard Ehrenborg, Gábor Hetyei, Margaret Readdy
The full root polytope of type is the convex hull of all pairwise differences of the standard basis vectors which we represent by forward and backward arrows. We completely cla…
Some combinatorial identities appearing in the calculation of the cohomology of Siegel modular varieties
Richard Ehrenborg, Sophie Morel, Margaret Readdy
In the computation of the intersection cohomology of Shimura varieties, or of the cohomology of equal rank locally symmetric spaces, combinatorial identities involving averag…
-Stirling numbers revisited
Yue Cai, Richard Ehrenborg, Margaret A. Readdy
We give combinatorial proofs of -Stirling identities using restricted growth words. This includes a poset theoretic proof of Carlitz's identity, a new proof of the -Frobenius…
The Gaussian coefficient revisited
Richard Ehrenborg, Margaret A. Readdy
We give a new --analogue of the Gaussian coefficient, also known as the -binomial which, like the original -binomial , is symmetric…
Simion's type associahedron is a pulling triangulation of the Legendre polytope
Richard Ehrenborg, Gabor Hetyei, Margaret Readdy
We show that Simion's type associahedron is combinatorially equivalent to a pulling triangulation of a type root polytope called the Legendre polytope. Furthermore, we show…
The van der Waerden complex
Richard Ehrenborg, Likith Govindaiah, Peter S. Park +1
We introduce the van der Waerden complex defined as the simplicial complex whose facets correspond to arithmetic progressions of length in the vertex set $\{1,…
q-Stirling numbers: A new view
Yue Cai, Margaret A. Readdy
We show the classical -Stirling numbers of the second kind can be expressed compactly as a pair of statistics on a subset of restricted growth words. The resulting expressions a…
A poset view of the major index
Richard Ehrenborg, Margaret Readdy
We introduce the Major MacMahon map and show how this map interacts with the pyramid and bipyramid operators. When the Major MacMahon map is applied to the ab-index of a simplicial…
Bruhat and balanced graphs
Richard Ehrenborg, Margaret Readdy
We generalize chain enumeration in graded partially ordered sets by relaxing the graded, poset and Eulerian requirements. The resulting balanced digraphs, which include the classic…
Manifold arrangements
Richard Ehrenborg, Margaret Readdy
We determine the cd-index of the induced subdivision arising from a manifold arrangement. This generalizes earlier results in several directions: (i) One can work with manifolds ot…
Euler flag enumeration of Whitney stratified spaces
Richard Ehrenborg, Mark Goresky, Margaret Readdy
The flag vector contains all the face incidence data of a polytope, and in the poset setting, the chain enumerative data. It is a classical result due to Bayer and Klapper that for…
The Rees product of posets
Patricia Muldoon Brown, Margaret A. Readdy
We determine how the flag f-vector of any graded poset changes under the Rees product with the chain, and more generally, any t-ary tree. As a corollary, the Möbius function of the…
On the non-existence of an R-labeling
Richard Ehrenborg, Margaret Readdy
We present a family of Eulerian posets which does not have any R-labeling. The result uses a structure theorem for R-labelings of the butterfly poset.
Exponential Dowling structures
Richard Ehrenborg, Margaret Readdy
The notion of exponential Dowling structures is introduced, generalizing Stanley's original theory of exponential structures. Enumerative theory is developed to determine the Möbiu…
The Möbius function of partitions with restricted block size
Richard Ehrenborg, Margaret Readdy
We study filters in the partition lattice formed by restricting to partitions by type. The Möbius function is determined in terms of the easier-to-compute descent set statistics on…
Level Eulerian Posets
Richard Ehrenborg, Gábor Hetyei, Margaret Readdy
The notion of level posets is introduced. This class of infinite posets has the property that between every two adjacent ranks the same bipartite graph occurs. When the adjacency m…
Enumerative and asymptotic analysis of a moduli space
Margaret A. Readdy
We focus on combinatorial aspects of the Hilbert series of the cohomology ring of the moduli space of stable pointed curves of genus zero. We show its graded Hilbert series satisfi…
Affine and toric hyperplane arrangements
Richard Ehrenborg, Margaret Readdy, MLE Slone
We extend the Billera-Ehrenborg-Readdy map between the intersection lattice and face lattice of a central hyperplane arrangement to affine and toric hyperplane arrangements. For ar…
Cyclotomic factors of the descent set polynomial
Denis Chebikin, Richard Ehrenborg, Pavlo Pylyavskyy +1
We introduce the notion of the descent set polynomial as an alternative way of encoding the sizes of descent classes of permutations. Descent set polynomials exhibit interesting fa…