Richard Ehrenborg, Kalle Karu
We prove a decomposition theorem for the cd-index of a Gorenstein* poset analogous to the decomposition theorem for the intersection cohomology of a toric variety. From this we settle a conjecture of Stanley that the cd-index of Gorenstein* lattices is minimized on Boolean algebras.
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As is well known, h-vectors of simple (or simplicial) convex polytopes are characterized. In fact, those h-vectors must satisfy Dehn-Sommerville equations and some other inequalities. Simple convex polytopes determine Gorenstein* simplicial posets and h-vectors are defined for simplicial posets. It is known that h-vectors of Gorenstein* simplicial posets must satisfy Dehn-Sommerville equations and that every component in the h-vectors must be non-negative. In this paper we will show that h-vectors of Gorenstein* simplicial posets must satisfy one more subtle condition conjectured by R. Stanley…
We introduce Artinian Gorenstein algebras defined by the face posets of regular polyhedra. We consider the strong Lefschetz property and Hodge--Riemann relation for the algebras. We show the strong Lefschetz property of the algebras for all Platonic solids. On the other hand, for some Platonic solids, we show that the algebras do not satisfy the Hodge--Riemann relation with respect to some strong Lefschetz elements.
Triangle equivalences between Gorenstein tiled orders and incidence algebras of posets
本文研究了Gorenstein铺砌阶环与有限偏序集的incidence算代数之间的三角等价关系，并探讨了相关偏序集在分级Morita等价和覆盖下的行为，最后对满足特定条件的Gorenstein铺砌阶环进行了分类。
Gorenstein braid cones and crepant resolutions
本研究将偏序集对应到辫锥及扇集，证明扇集定义的光滑环面簇是锥对应奇异环面簇的 crepant 消解的充要条件，揭示环面簇的 Gorenstein 性质与偏序集结构的关联并验证相关猜想。
We give a characterization of Gorenstein toric Fano varieties of dimension $n$ with index $n$ among toric varieties. As an application, we give a strong version of Fujita's freeness conjecture and also give a simple proof of Fujita's very ampleness conjecture on Gorenstein toric varieties.
The number of flags in a complete fan, or more generally in an Eulerian poset, is encoded in the cd-index. We prove non-negativity of the cd-index for complete fans, regular CW-spheres and Gorenstein* posets.
Let $P$ be a finite poset, $K$ a field, and $O(P)$ (resp. $C(P)$) the order (resp. chain) polytope of $P$. We study the non-Gorenstein locus of $E_K[O(P)]$ (resp. $E_K[C(P)]$), the Ehrhart ring of $O(P)$ (resp. $C(P)$) over $K$, which are each normal toric rings associated $P$. In particular, we show that the dimension of non-Gorenstein loci of $E_K[O(P)]$ and $E_K[C(P)]$ are the same. Further, we show that $E_K[C(P)]$ is nearly Gorenstein if and only if $P$ is the disjoint union of pure posets $P_1, \ldots, P_s$ with $|\mathrm{rank} P_i-\mathrm{rank} P_j|\leq 1$ for any $i$ and $j$.
Stellahedral geometry of partially ordered sets
本文提出偏序集的星状变换，保持欧拉性等性质，并证明其与环面h-多项式联系，从而得出增广Chow多项式的正性结果，并否定两个开放问题。
In this paper, we introduce a new algebraic concept, which we call squarefree P-modules. This concept is inspired from Karu's proof of the non-negativity of the cd-indices of Gorenstein* posets, and supplies a way to study cd-indices from the viewpoint of commutative algebra. Indeed, by using the theory of squarefree P-modules, we give several new algebraic and combinatorial results on CW-posets. First, we define an analogue of the cd-index for any CW-poset and prove its non-negativity when a CW-poset is Cohen-Macaulay. This result proves that the h-vector of the barycentric subdivision of a C…
We give a characterizaion of Gorenstein toric Fano $n$-folds with index $n-1$, which is called Gorenstein toric Del Pezzo $n$-folds, among toric varieties. In practice, we obtain a condition for a lattice $n$-polytope to be a Gorenstein Fano polytope. In our proof, we do not use Batyrev-Juny's classification of Gorenstein Fano polytopes.
Sharp volume and multiplicity bounds for Fano simplices
该研究给出依赖维度和Gorenstein指数的法诺单纯形体积、马勒体积与重数的精确上界，提出高效分类方法并完成多种Gorenstein指数下四维及以下法诺单纯形的分类。
In this paper, we define posets of types B, C, and D. These posets encode the matrix forms of certain Lie algebras which lie between the algebras of upper-triangular and diagonal matrices. Interestingly, such type-B, C, and D Lie poset algebras can be related to Reiner's notion of a parset. Our primary concern is the index and spectral theories of type-B, C, and D Lie poset algebras. For an important restricted class, we develop combinatorial index formulas and, in particular, characterize posets corresponding to Frobenius Lie algebras. In this latter case we show that the spectrum is binary; …
The $cd$-index of semi-Eulerian posets
本文把 Euler 偏序集的 $cd$-指标推广至半 Euler 偏序集，并证明单纯半 Euler Buchsbaum 偏序集的系数非负，从而证实并扩展 Novik 猜想。
Poset Partitions and the Combinatorics of the $\textbf{cd}$-Index
本文提出了一种新的欧拉 poset 类，称为 S-分割 poset，证明其具有非负的 cd 指数，并引入了 SE-分割 poset 的半欧拉版本。
We provide general closed-form formulas for the index of type-A Lie poset algebras corresponding to posets of restricted height. Furthermore, we provide a combinatorial recipe for constructing all posets corresponding to type-A Frobenius Lie poset algebras of heights zero, one, and two. A finite Morse theory argument establishes that the simplicial realization of such posets is contractible. It then follows, from a recent theorem of Coll and Gerstenhaber, that the second Lie cohomology group of the corresponding Lie poset algebra with coefficients in itself is zero. Consequently, the Lie poset…
The cd-index is an invariant of Eulerian posets expressed as a polynomial in noncommuting variables c and d. It determines another invariant, the h-polynomial. In this paper, we study the relative setting, that of subdivisions of posets. We introduce the mixed cd-index, an invariant of strong formal subdivisions of posets, which determines the mixed h-polynomial introduced by the second author with Stapledon. The mixed cd-index is a polynomial in noncommuting variables c',d',c,d, and e and is defined in terms of the local cd-index of Karu. Here, use is made of the decomposition theorem for the…
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 poset, it yields the q-analogue of n! times the h-polynomial of the poset. Applying the map to the Boolean algebra gives the distribution of the major index on the symmetric group, a seminal result due to MacMahon. Similarly, when applied to the cross-polytope we obtain the distribution of one of the major indexes on signed permutations due to Reiner.
This thesis aims to give the reader an introduction and overview of the cd-index of a poset, as well as establish some new results. We give a combinatorial proof of Ehrenborg and Karu's cd-index subdivision decomposition for Gorenstein* complexes and extend it to a wider class of subdivisions. In doing so, we define a local cd-index that behaves analogously to the well studied local h-vector. We examine known cd-index and h-vector bounds, and then use the local cd-index to bound a particular class of polytopes with the cd-index of a stacked polytope. We conclude by investigating the h-vector a…
Decomposing Gorenstein polytopes of large index
本文证明了大指标 Gorenstein 多胞体的自由并分解定理，推广了 Batyrev-Juny 金字塔定理，并应用于弦论 E-多项式的消失性判定，证实了相关猜想。
In this paper we show that the spectrum of the Q-codegree of a d-dimensional lattice polytope is finite above any positive threshold in the class of lattice polytopes with α-canonical normal fan for any fixed α>0. For α=1/r this includes lattice polytopes with Q-Gorenstein normal fan of index r. In particular, this proves Fujita's Spectrum Conjecture for polarized varieties in the case of Q-Gorenstein toric varieties of index r.
The purpose of this paper is to review some combinatorial ideas behind the mirror symmetry for Calabi-Yau hypersurfaces and complete intersections in Gorenstein toric Fano varieties. We suggest as a basic combinatorial object the notion of a Gorenstein polytope of index r. A natural combinatorial duality for d-dimensional Gorenstein polytopes of index r extends the well-known polar duality for reflexive polytopes (case r=1). We consider the Borisov duality between two nef-partitions as a duality between two Gorenstein polytopes P and P^* of index r together with selected special (r-1)-dimensio…
This is a survey of the $cd$-index of Eulerian partially ordered sets. The $cd$-index is an encoding of the numbers of chains, specified by ranks, in the poset. It is the most efficient such encoding, incorporating all the affine relations on the flag numbers of Eulerian posets. Eulerian posets include the face posets of regular CW spheres (in particular, of convex polytopes), intervals in the Bruhat order on Coxeter groups, and the lattices of regions of oriented matroids. The paper discusses inequalities on the $cd$-index, connections with other combinatorial parameters, computation, and alg…
A Gorenstein polytope of index r is a lattice polytope whose r-th dilate is a reflexive polytope. These objects are of interest in combinatorial commutative algebra and enumerative combinatorics, and play a crucial role in Batyrev's and Borisov's computation of Hodge numbers of mirror-symmetric generic Calabi-Yau complete intersections. In this paper, we report on what is known about smooth Gorenstein polytopes, i.e., Gorenstein polytopes whose normal fan is unimodular. We classify d-dimensional smooth Gorenstein polytopes with index larger than (d+3)/3. Moreover, we use a modification of Oebr…
Contact Lie poset algebras of types B, C, and D
本文推广 B、C、D 型 Lie 偏序集代数的组合指标公式，并据此用关联图刻画高度为一偏序集对应的接触 Lie 偏序集代数。
Extending the ab-index
该研究针对有限分次有界偏序集，证明Poincaré扩展的ab-index可通过Ω变换从ab-index得到，验证了相关猜想，为R-标记偏序集外的ab-index和Chow多项式提供了更具概念性的研究路径。
Existence of Kähler algebras with Chow polynomials as Hilbert series
本文研究了弱排名偏序的Chow多项式，证明了存在具有特定Hilbert-Poincaré级数的Kähler代数，并展示了Chow多项式系数的对数凹性及更高排名的反例。
The Poincaré-extended ab-index
受超平面配置相交偏序集的Igusa局部zeta函数相关猜想启发，研究人员提出庞加莱扩展ab-指数，证明相关系数非负性与多个猜想，定义拉回ab-指数，统一推广已有结果并提出Schur正性猜想。
Wiener Indices of Minuscule Lattices
本文研究微小偏序集中序理想的分配格的维纳指数，给出了精确表达式，并分析了无限族中随机序理想间距离的渐近分布。
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 face lattices of polytopes, and more generally, Eulerian graded posets, the flag vector can be written as a cd-index, a non-commutative polynomial which removes all the linear redundancies among the flag vector entries. This result holds for regular CW complexes. We relax the regularity condition to show the cd-index exists for Whitney stratified manifolds by extending the notion of a graded poset to that of a quasi…
We introduce two new partial orders on the standard Young tableaux of a given partition shape, in analogy with the strong and weak Bruhat orders on permutations. Both posets are ranked by the major index statistic offset by a fixed shift. The existence of such ranked poset structures allows us to classify the realizable major index statistics on standard tableaux of arbitrary straight shape and certain skew shapes. By a theorem of Lusztig--Stanley, this classification can be interpreted as determining which irreducible representations of the symmetric group exist in which homogeneous component…
Many combinatorial proofs rely on induction. When these proofs are formulated in traditional language, they can be bulky and unmanageable. Coalgebras provide a language which can reduce reduce many inductive proofs in graded poset theory to comprehensible size. As a bonus, the visual form of the resulting recursive proofs suggests combinatorial interpretations for constants appearing in the longer arguments. We use the techniques of coalgebras to compute invariants of toric and affine arrangements as well as of poset products. In additional chapters we prove structure theorems for acyclic orie…
We generalize chain enumeration in graded partially ordered sets by relaxing the graded, poset and Eulerian requirements. The resulting balanced digraphs, which include the classical Eulerian posets having an $R$-labeling, imply the existence of the (non-homogeneous) ${\bf cd}$-index, a key invariant for studying inequalities for the flag vector of polytopes. Mirroring Alexander duality for Eulerian posets, we show an analogue of Alexander duality for balanced digraphs. For Bruhat graphs of Coxeter groups, an important family of balanced graphs, our theory gives elementary proofs of the existe…
Billey-Postnikov posets, rationally smooth Schubert varieties, and Poincaré duality
本文发展了 Billey-Postnikov 分解理论，证明有限型中可由模式条件识别，并应用于有理光滑 Schubert 簇的结构常数三角性和 Poincaré 对偶，同时分类了有限型中允许广义 Lehmer 码的有理光滑 Bruhat 区间，并否定了无限型中的相关猜想。
A refinement of the edge theorem for order and chain polytopes
本文改进序多面体与链多面体的边定理，通过连通凸子集划分边并证明对应类基数相等，给出边数闭式公式，并揭示已知双射的结构，同时比较边方向、边长与直径，讨论对组合优化的影响。
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