Axel Werner
We consider unimodality and related properties of f-vectors of polytopes in various dimensions. By a result of Kalai (1988), f-vectors of 5-polytopes are unimodal. In higher dimensions much less can be said; we give an overview on current results and present a potentially interesting construction as well as a conjecture arising from this.
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Although the Unimodality Conjecture holds for some certain classes of cubical polytopes (e.g. cubes, capped cubical polytopes, neighborly cubical polytopes), it fails for cubical polytopes in general. A 12-dimensional cubical polytope with non-unimodal face vector is constructed by using capping operations over a neighborly cubical polytope with 2 to the power 131 vertices. For cubical polytopes, the Unimodality Conjecture is proved for dimensions less than 11. The first one-third of the face vector of a cubical polytope is increasing and its last one-third is decreasing in any dimension.
It is a famous open question whether every integrally closed reflexive polytope has a unimodal Ehrhart delta-vector. We generalize this question to arbitrary integrally closed lattice polytopes and we prove unimodality for the delta-vector of lattice parallelepipeds. This is the first nontrivial class of integrally closed polytopes. Moreover, we suggest a new approach to the problem for reflexive polytopes via triangulations.
An interesting open problem in Ehrhart theory is to classify those lattice polytopes having a unimodal $h^*$-vector. Although various sufficient conditions have been found, necessary conditions remain a challenge. In this paper, we consider integrally closed reflexive simplices and discuss an operation that preserves reflexivity, integral closure, and unimodality of the $h^*$-vector, providing one explanation for why unimodality occurs in this setting. We also discuss the failure of proving unimodality in this setting using weak Lefschetz elements.
Cyclic polytopes are generally known for being involved in the Upper Bound Theorem, but they have another extremal property which is less well known. Namely, the special shape of their f-vectors makes them applicable to certain constructions to present non-unimodal convex polytopes. Nevertheless, the f-vectors of cyclic polytopes themselves are unimodal.
We prove the unimodality of the Ehrhart $δ$-polynomial of the chain polytope of the zig-zag poset, which was conjectured by Kirillov. First, based on a result due to Stanley, we show that this polynomial coincides with the $W$-polynomial for the zig-zag poset with some natural labeling. Then, its unimodality immediately follows from a result of Gasharov, which states that the $W$-polynomials of naturally labeled graded posets of rank $1$ or $2$ are unimodal.
In this paper, we investigate two properties concerning the unimodality of the $δ$-vectors of lattice polytopes, which are log-concavity and alternatingly increasingness. For lattice polytopes $\mathcal{P}$ of dimension $d$, we prove that the dilated lattice polytopes $n\mathcal{P}$ have strictly log-concave and strictly alternatingly increasing $δ$-vectors if $n > \max\{s,d+1-s\}$, where $s$ is the degree of the $δ$-polynomial of $\mathcal{P}$. The bound $\max\{s,d+1-s\}$ for $n$ is reasonable. We also provide several kinds of unimodal (or non-unimodal) $δ$-vectors. Concretely, we give exampl…
For a given lattice polytope, two fundamental problems within the field of Ehrhart theory are to (1) determine if its (Ehrhart) $h^\ast$-polynomial is unimodal and (2) to determine if its Ehrhart polynomial has only positive coefficients. The former property of a lattice polytope is known as Ehrhart unimodality and the latter property is known as Ehrhart positivity. These two properties are often simultaneously conjectured to hold for interesting families of lattice polytopes, yet they are typically studied in parallel. As to answer a question posed at the 2017 Introductory Workshop to the MSR…
Ehrhart theory is the study of sequences recording the number of integer points in non-negative integral dilates of rational polytopes. For a given lattice polytope, this sequence is encoded in a finite vector called the Ehrhart $h^*$-vector. Ehrhart $h^*$-vectors have connections to many areas of mathematics, including commutative algebra and enumerative combinatorics. In this survey we discuss what is known about unimodality for Ehrhart $h^*$-vectors and highlight open questions and problems.
Unimodality of the number of paths per length on polytopes: Examples, counterexamples, and a central limit theorem
该研究针对凸多面体路径数的单峰性猜想，证实部分多面体类符合猜想、构造反例否定其普遍性，并证明球面上均匀顶点的随机多面体相干路径长度满足中心极限定理。
On Preserving or Reversing Higher-Order Unimodality and Convexity by Sign-Regular Kernels
本文刻画符号正则核变换保持或逆转序列单峰性、凸性的三阶全正/全负条件，并推广到高阶凸、多峰及同核序列商情形。
Unimodality shenanigans in Ehrhart theory
本文通过构造矩形棱柱的 Cayley 和，否证了 Stanley、Brenti 及 Ferroni-Higashitani 关于 IDP 多胞体 $h^*$-多项式单峰性与对数凹性的多个猜想，并给出光滑反例。
We show that h*-vectors of alcoved polytopes P in R^n (of Lie type A) are unimodal if they contain interior lattice points and their facets have lattice distance 1 to the set of interior lattice points. The maximal possible such distance for general alcoved polytopes is shown to be dim(P)-1. A secondary purpose of the paper is to serve as a guide to previous work surrounding unimodality of h*-vectors of alcoved polytopes and related questions.
A long-standing open conjecture in combinatorics asserts that a Gorenstein lattice polytope with the integer decomposition property (IDP) has a unimodal (Ehrhart) $h^\ast$-polynomial. This conjecture can be viewed as a strengthening of a previously disproved conjecture which stated that any Gorenstein lattice polytope has a unimodal $h^\ast$-polynomial. The first counterexamples to unimodality for Gorenstein lattice polytopes were given in even dimensions greater than five by Musta{ţ}{ǎ} and Payne, and this was extended to all dimensions greater than five by Payne. While there exist numerous e…
Through tropical normal idempotent matrices, we introduce isocanted alcoved polytopes, computing their $f$--vectors and checking the validity of the following five conjectures: Bárány, unimodality, $3^d$, flag and cubical lower bound (CLBC). Isocanted alcoved polytopes are centrally symmetric, almost simple cubical polytopes. They are zonotopes. We show that, for each dimension, there is a unique combinatorial type. In dimension $d$, an isocanted alcoved polytope has $2^{d+1}-2$ vertices, its face lattice is the lattice of proper subsets of $[d+1]$ and its diameter is $d+1$. They are realizati…
Newton polytopes of dual Schubert polynomials
本文完整刻画了对偶舒伯特多项式的支撑集，为Huh等人2022年证明的M-凸性提供了初等替代证明，并进一步组合刻画了其牛顿多面体的顶点。
We study a combinatorial notion where given a set of lattice points one takes the set of all sums of subsets of a fixed size, and we ask if the given set comes from a convex lattice polytope whether the resulting set also comes from a convex lattice polytope. We obtain a positive result in dimension 2 and a negative result in higher dimensions. We apply this to the corner cut polyhedron.
Lattice polytopes of large width have real-rooted Ehrhart $h^*$-polynomials
该研究证明固定维数下宽幅格多面体的Ehrhart h*-多项式为实根，还给出格单纯形局部h*-多项式的类似结论，解答了相关问题，证明借助ChatGPT 5.6 Sol完成。
The notions of convexity and convex polytopes are introduced in the setting of tropical geometry. Combinatorial types of tropical polytopes are shown to be in bijection with regular triangulations of products of two simplices. Applications to phylogenetic trees are discussed. Theorem 29 and Corollary 30 in the paper, relating tropical polytopes to injective hulls, are incorrect. See the erratum at http://www.math.uiuc.edu/documenta/vol-09/vol-09-eng.html .
Intersection Bodies of Polytopes: Translations and Convexity
本文研究多面体相交体在平移下的行为，引入仿射超平面配置证明边界多项式的扩展性，并完整刻画二维下相交体为凸的多边形及一般维度的部分刻画。
We study semigroup algebras arising from lattice polytopes, compute their volume polynomials (particularizing work of Hochster), and establish strong Lefschetz properties (generalizing work of the first three authors). This resolves several conjectures concerning unimodality properties of the $h^\ast$-polynomial of lattice polytopes arising within Ehrhart theory.
Lattice polytopes and semigroup algebras: Generic Lefschetz properties and Parseval-Rayleigh identities
本文研究与格多面体相关联的半群代数，通过推广Hochster的工作，利用Parseval-Rayleigh恒等式与微分方程描述其体积映射并建立强Lefschetz性质，进而解决了关于h*-多项式单峰性的若干猜想。
Exterior Cyclic Polytopes and Convexity of Amplituhedra
本文引入可扩张凸性与外循环多面体，证明 k=m=2 的 amplituhedron 在 Grassmann 流形中可扩张凸，并构造经 twist 映射改变数据的对偶 amplituhedron。
We establish a new notion of tropical convexity for signed tropical numbers. We provide several equivalent descriptions involving balance relations and intersections of open halfspaces as well as the image of a union of polytopes over Puiseux series and hyperoperations. Along the way, we deduce a new Farkas lemma and Fourier-Motzkin elimination without the non-negativity restriction on the variables. This leads to a Minkowski-Weyl theorem for polytopes over the signed tropical numbers.
Inequalities for $f^*$-vectors of Lattice Polytopes
本文研究了格多面体 $f^*$-向量的系数不等式，揭示了其与单纯多面体 $f$-向量不等式的相似性，并证明了特定多面体族的单峰性及 $h^*$-向量相同条件下的单峰 $f^*$-向量存在性。
A stacking operation adds a $d$-simplex on top of a facet of a simplicial $d$-polytope while maintaining the convexity of the polytope. A stacked $d$-polytope is a polytope that is obtained from a $d$-simplex and a series of stacking operations. We show that for a fixed $d$ every stacked $d$-polytope with $n$ vertices can be realized with nonnegative integer coordinates. The coordinates are bounded by $O(n^{2\log(2d)})$, except for one axis, where the coordinates are bounded by $O(n^{3\log(2d)})$. The described realization can be computed with an easy algorithm. The realization of the polytope…
Using tropical convexity Dochtermann, Fink, and Sanyal proved that regular fine mixed subdivisions of Minkowski sums of simplices support minimal cellular resolutions. They asked if the regularity condition can be removed. We give an affirmative answer by a different method. A new easily checked sufficient condition for a subdivided polytope to support a cellular resolution is proved. The main tool used is discrete Morse theory.
Ehrhart Properties under Operations on Lattice Polytopes
本文研究格多胞体上八种运算（如笛卡尔积、闵可夫斯基和等）对三类Ehrhart性质（系数正性、$h^*$-多项式系数性质、几何性质）的保持性，通过建立保持定理或构造反例，并探讨非保持情形下的充分或等价条件。
This is a survey on tropical polytopes from the combinatorial point of view and with a focus on algorithms. Tropical convexity is interesting because it relates a number of combinatorial concepts including ordinary convexity, monomial ideals, subdivisions of products of simplices, matroid theory, finite metric spaces, and the tropical Grassmannians. The relationship between these topics is explained via one running example throughout the whole paper. The final section explains how the new version 2.9.4 of the software system polymake can be used to compute with tropical polytopes.
A polytrope is a tropical polytope which at the same time is convex in the ordinary sense. A $d$-dimensional polytrope turns out to be a tropical simplex, that is, it is the tropical convex hull of $d+1$ points. This statement is equivalent to the known fact that the Segre product of two full polynomial rings (over some field $K$) has the Gorenstein property if and only if the factors are generated by the same number of indeterminates. The combinatorial types of polytropes up to dimension three are classified.
Examples and counterexamples in Ehrhart theory
本文综述Ehrhart多项式和$h^*$-多项式系数的不等式，构造反例否定IDP多胞形相关猜想的变体，并首次揭示Ehrhart正性与实根性的联系。
Boundary $h^\ast$-vectors and unimodular triangulations
本文通过正则单模三角剖分和 toric 理想的 Gröbner 衰减研究了格点多面体边界上的 $h^\ast$-多项式，推导了边界 $h^\ast$-多项式与正则单模三角剖分 $h$-多项式的关系，并建立了德恩-索默维尔型关系。
Tightness of a triangulated manifold is a topological condition, roughly meaning that any simplexwise linear embedding of the triangulation into euclidean space is "as convex as possible". It can thus be understood as a generalization of the concept of convexity. In even dimensions, super-neighborliness is known to be a purely combinatorial condition which implies the tightness of a triangulation. Here we present other sufficient and purely combinatorial conditions which can be applied to the odd-dimensional case as well. One of the conditions is that all vertex links are stacked spheres, whic…
Convex unions and completions from simplicial pseudomanifolds
研究通过单纯伪流形的泛化，探讨PL同胚对局部凸性的影响，揭示了收缩边对凸性空间的显著影响。
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