对称多胞形的极值性质及其应用

凸多胞形现代理论的主要成就是被称之为Dehn-Sommerville关系的上界定理和下界定理,它们属于凸多胞形的经典组合理论.本文建立了关于对称凸多胞形的两个极值定理,它们可视为凸多胞形度量理论中的上界定理和下界定理,另外给出了两个极值定理的一个应用.     

关于多胞形一个新仿射不变量的应用

用组合极值方法导出了n维欧氏空间中关于原点对称的一个凸多胞形子类上一个新的仿射不变量(最近由Lutwak,Yang和Zhang引入)的解析表达式,并给出了其在凸多胞形Minkowski问题的一个应用．     

广义重心坐标与凸多胞形的性质

提出n维欧氏空间中广义重心坐标的概念,建立了广义重心坐标下两点间的距离公式,并利用于研究凸多胞形的若干性质,将欧氏平面上凸多边形的一些定值与极值性质推广到n维空间.     

中心仿射不变量的推广及其比的极值问题

本文研究了关于投影体的中心仿射不变量比的问题.借助定义一个新的中心仿射不变量W(P)把已有结论中的研究对象从中心对称凸多胞形,推广到一般中心对称凸体,并求得推广后的极值.     

锥体积泛函与仿射不等式(英文)

本文研究了凸多胞形的锥体积泛函.利用投影体以及Lutwak、杨和张最近所建立的仿射等周不等式,得到了刻划平行四边形特征的一个崭新不等式和用锥体积泛函以及投影体的体积所表达的关于配极体体积的严格下界.     

预给二面角的m面凸多胞形嵌入Rd的充分必要条件

本文给出了预给二面角的ｍ面凸多胞形嵌入Ｒ^d的充分必要条件     

多复变数准凸映射的偏差定理

首先给出了C~n中单位多圆柱D~n上准凸映射f关于Jacobin矩阵J_f(z)的偏差定理.该定理是单位圆盘凸函数的偏差定理在多复变中的推广.其次得到了Banach空间单位球上准凸映射的偏差定理的上界.最后给出了关于准凸映射偏差定理的两个猜想.     

多复变数星形映射在某方向上精确的偏差定理

研究了Cn中单位多圆柱上星形映射在某方向上精确的偏差定理．给出了复Banach空间单位球的某方向上精确的偏差的上界,同时给出了下界的猜测．     

强α型螺形映照的偏差上界估计

利用强α型螺形映照的增长定理及推广的RDper-Suffridge算子的性质,讨论有界平衡域上强α型螺形映照的偏差上界,并作为特殊情况得到C~n中单位球B~n上强α型螺形映照的偏差上界估计以及强星形映照的偏差上界估计.所得结论丰富了对正规化双全纯映照的偏差的研究.     

超凸空间中的连续选择定理与耦合定理

本文给出了超凸空间中的连续选择定理与耦合定理，并得到了它们的证明,作为应用，我们给出了超凸空间中的不动点定理与截口定理．     

Signable posets and partitionable simplicial complexes

The notion of apartitionable simplicial complex is extended to that of asignable partially ordered set. It is shown in a unified way that face lattices of shellable polytopal complexes, polyhedral cone fans, and oriented matroid polytopes, are all signable. Each of these classes, which are believed to be mutually incomparable, strictly contains the class of convex polytopes. A general sufficient condition, termedtotal signability, for a simplicial complex to satisfy McMullen's Upper Bound Theorem on the numbers of faces, is provided. The simplicial members of each of the three classes above are concluded to be partitionable and to satisfy the upper bound theorem. The computational complexity of face enumeration and of deciding partitionability is discussed. It is shown that under a suitable presentation, the face numbers of a signable simplicial complex can be efficiently computed. In particular, the face numbers of simplicial fans can be computed in polynomial time, extending the analogous statement for convex polytopes. The research of S. Onn was supported by the Alexander von Humboldt Stifnung, by the Fund for the Promotion of Research at the Technion, and by Technion VPR fund 192–198.     

A New Lower Bound Theorem for Combinatorial 2k-Manifolds

We prove a centrally-symmetric analogue of the generalized Heawood inequality, i.e. we prove a Lower Bound Theorem for combinatorial 2k-manifolds M whose convex hull is a centrally-symmetric simplicial polytope P under the additional assumptions that M is a subcomplex of the boundary complex of P and that M contains the k-skeleton of P. We also deduce a relation for the minimum number of vertices of a combinatorial 2k-manifold satisfying our Lower Bound. Received June 12, 1996 Revised June 9, 1997     

P.L.-Spheres,convex polytopes,and stress

We describe here the notion of generalized stress on simplicial complexes, which serves several purposes: it establishes a link between two proofs of the Lower Bound Theorem for simplicial convex polytopes; elucidates some connections between the algebraic tools and the geometric properties of polytopes; leads to an associated natural generalization of infinitesimal motions; behaves well with respect to bistellar operations in the same way that the face ring of a simplicial complex coordinates well with shelling operations, giving rise to a new proof that p.l.-spheres are Cohen-Macaulay; and is dual to the notion of McMullen's weights on simple polytopes which he used to give a simpler, more geometric proof of theg-theorem. Supported in part by NSF Grants DMS-8504050 and DMS-8802933, by NSA Grant MDA904-89-H-2038, by the Mittag-Leffier Institute, by DIMACS (Center for Discrete Mathematics and Theoretical Computer Science), a National Science Foundation Science and Technology Center, NSF-STC88-09648, and by a grant from the EPSRC.     

A short proof of rigidity of convex polytopes

We present a much simplified proof of Dehn’s theorem on the infinitesimal rigidity of convex polytopes. Our approach is based on the ideas of Trushkina [1] and Schramm [2].     

Subpolytopes of stack polytopes

A polytopeP is called asubpolytope of a polytopeQ if vertP ⊆ vertQ. The purpose of this paper is to construct examples of 3-dimensional polytopes which are not subpolytopes of stack polytopes. Previously no such examples were known. For the properties of convex polytopes and an explanation of the standard terminology and notation used here, see B. Grünbaum,Convex Polytopes, London-New York-Sydney, 1967, or P. McMullen and G. C. Shephard,Convex Polytopes and the Upper Bound Conjecture, London Mathematical Society Lecture Note Series Volume 3, Cambridge, 1971.     

On permutation polytopes

In this paper we lay the foundations for the study of permutation polytopes: the convex hull of a group of permutation matrices.We clarify the relevant notions of equivalence, prove a product theorem, and discuss centrally symmetric permutation polytopes. We provide a number of combinatorial properties of (faces of) permutation polytopes. As an application, we classify ?4-dimensional permutation polytopes and the corresponding permutation groups. Classification results and further examples are made available online.We conclude with several questions suggested by a general finiteness result.     

Normal polytopes: Between discrete,continuous, and random

The first three sections of this survey represent an updated and much expanded version of the abstract of my talk at FPSAC'2010: new results are incorporated and several concrete conjectures on the interactions between the three perspectives on normal polytopes in the title are proposed. The last section outlines new challenges in general convex polytopes, motivated by the study of normal polytopes.     

Facets and volume of Gorenstein Fano polytopes

It is known that every integral convex polytope is unimodularly equivalent to a face of some Gorenstein Fano polytope. It is then reasonable to ask whether every normal polytope is unimodularly equivalent to a face of some normal Gorenstein Fano polytope. In the present paper, it is shown that, by giving new classes of normal Gorenstein Fano polytopes, each order polytope as well as each chain polytope of dimension d is unimodularly equivalent to a facet of some normal Gorenstein Fano polytopes of dimension . Furthermore, investigation on combinatorial properties, especially, Ehrhart polynomials and volume of these new polytopes will be achieved. Finally, some curious examples of Gorenstein Fano polytopes will be discovered.