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     

Open problems on k-orbit polytopes

We present 35 open problems on combinatorial, geometric and algebraic aspects of $k$-orbit abstract polytopes. We also present a theory of rooted polytopes that has appeared implicitly in previous work but has not been formalized before.     

On locally spherical polytopes of type {5, 3, 5}

There are only finitely many locally projective regular polytopes of type {5, 3, 5}. They are covered by a locally spherical polytope whose automorphism group is J₁×J₁×L₂(19), where J₁ is the first Janko group, of order 175560, and L₂(19) is the projective special linear group of order 3420. This polytope is minimal, in the sense that any other polytope that covers all locally projective polytopes of type {5, 3, 5} must in turn cover this one.     

The equipartition polytope. I: Formulations,dimension and basic facets

The following basic clustering problem arises in different domains, ranging from physics, statistics and Boolean function minimization.Given a graphG = (V, E) and edge weightsc _e , partition the setV into two sets of 1/2|V| and 1/2|V| nodes in such a way that the sum of the weights of edges not having both endnodes in the same set is maximized or minimized.Anequicut is a feasible solution of the above problem and theequicut polytope Q(G) is the convex hull of the incidence vectors of equicuts inG. In this paper we give some integer programming formulations of the equicut problem, study the dimension of the equicut polytope and describe some basic classes of facet-inducing inequalities forQ(G). Partial support of NSF grants DMS 8606188 and ECS 8800281.This work was done while these two authors visited IASI, Rome, in Spring 1987.     

Determination of Convex Bodies by Projection Functions

This paper is concerned with an investigation to what extent a convex body is determined by projection functions. We introduce the notion of convex bodies that are almost determined by their brightness function and give a geometric characterization of these bodies. We further prove that, for i 2,...,d–2, a polytope is determined by its ith projection function, if all of its (i+1)-faces are parallelepipeds. Both results extend work by Gardner and Voli [4].     

The equipartition polytope. II: Valid inequalities and facets

Theequipartition problem is defined as follows: given a graphG = (V, E) and edge weightsc _e , partition the setV into two sets of 1/2|V| and 1/2|V| nodes in such a way that the sum of the weights of edges not having both endnodes in the same set is maximized or minimized.Anequicut is a feasible solution of the above problem and theequicut polytope Q(G) is the convex hull of the incidence vectors of equicuts inG. In this paper we describe some facet inducing inequalities of this polytope.Partial support of NSF grants DMS 8606188 and ECS 8800281.This work was done while these two authors visited IASI, Rome, in Spring 1987.     

Gelfand-Tsetlin polytopes and Feigin-Fourier-Littelmann-Vinberg polytopes as marked poset polytopes

Stanley (1986) showed how a finite partially ordered set gives rise to two polytopes, called the order polytope and chain polytope, which have the same Ehrhart polynomial despite being quite different combinatorially. We generalize his result to a wider family of polytopes constructed from a poset P with integers assigned to some of its elements.Through this construction, we explain combinatorially the relationship between the Gelfand-Tsetlin polytopes (1950) and the Feigin-Fourier-Littelmann-Vinberg polytopes (2010, 2005), which arise in the representation theory of the special linear Lie algebra. We then use the generalized Gelfand-Tsetlin polytopes of Berenstein and Zelevinsky (1989) to propose conjectural analogues of the Feigin-Fourier-Littelmann-Vinberg polytopes corresponding to the symplectic and odd orthogonal Lie algebras.     

How to recycle your facets

We show how to transform any inequality defining a facet of some 0/1-polytope into an inequality defining a facet of the acyclic subgraph polytope. While this facet-recycling procedure can potentially be used to construct ‘nasty’ facets, it can also be used to better understand and extend the polyhedral theory of the acyclic subgraph and linear ordering problems.     

Forest covers and a polyhedral intersection theorem

Aforest cover of a graph is a spanning forest for which each component has at least two nodes. We consider the convex hull of incidence vectors of forest covers in a graph and show that this polyhedron is the intersection of the forest polytope and the cover polytope. This polytope has both the spanning tree and perfect matching polytopes as faces. Further, the forest cover polytope remains integral with the addition of the constraint requiring that, for some integerk, exactlyk edges be used in the solution.Research done while thae authors were visiting the Institut für Ökonometrie und Operations Research, Universität Bonn, West Germany.Financial support provided by the Natural Sciences and Engineering Research Council, Canada and the German Research Association (Deutsche Forschungsgemeneinschaft, SFB 303).     

Coxeter polytopes with a unique pair of non-intersecting facets

We consider compact hyperbolic Coxeter polytopes whose Coxeter diagram contains a unique dotted edge. We prove that such a polytope in d-dimensional hyperbolic space has at most d+3 facets. In view of results by Kaplinskaja [I.M. Kaplinskaya, Discrete groups generated by reflections in the faces of simplicial prisms in Lobachevskian spaces, Math. Notes 15 (1974) 88-91] and the second author [P. Tumarkin, Compact hyperbolic Coxeter n-polytopes with n+3 facets, Electron. J. Combin. 14 (2007), R69, 36 pp.], this implies that compact hyperbolic Coxeter polytopes with a unique pair of non-intersecting facets are completely classified. They do exist only up to dimension 6 and in dimension 8.     

An algorithm for finding extremal polytope norms of matrix families

In this paper the problem of the computation of the joint spectral radius of a finite set of matrices is considered. We present an algorithm which, under some suitable assumptions, is able to check if a certain product in the multiplicative semigroup is spectrum maximizing. The algorithm proceeds by attempting to construct a suitable extremal norm for the family, namely a complex polytope norm. As examples for testing our technique, we first consider the set of two 2-dimensional matrices recently analyzed by Blondel, Nesterov and Theys to disprove the finiteness conjecture, and then a set of 3-dimensional matrices arising in the zero-stability analysis of the 4-step BDF formula for ordinary differential equations.     

Gorenstein simplices with a given δ-polynomial

To classify the lattice polytopes with a given $\delta$-polynomial is an important open problem in Ehrhart theory. A complete classification of the Gorenstein simplices whose normalized volumes are prime integers is known. In particular, their $\delta$-polynomials are of the form $1+t^k+?+t^{(v?1)k}$, where $k$ and $v$ are positive integers. In the present paper, a complete classification of the Gorenstein simplices with the above $\delta$-polynomials will be performed, when $v$ is either $p^2$ or $pq$, where $p$ and $q$ are prime integers with $p\ne q$. Moreover, we consider the number of Gorenstein simplices, up to unimodular equivalence, with the expected $\delta$-polynomial.     

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．     

An Adaptive Algorithm for Vector Partitioning

The vector partition problem concerns the partitioning of a set A of n vectors in d-space into p parts so as to maximize an objective function c which is convex on the sum of vectors in each part. Here all parameters d, p, n are considered variables. In this paper, we study the adjacency of vertices in the associated partition polytopes. Using our adjacency characterization for these polytopes, we are able to develop an adaptive algorithm for the vector partition problem that runs in time O(q(L)v) and in space O(L), where q is a polynomial function, L is the input size and v is the number of vertices of the associated partition polytope. It is based on an output-sensitive algorithm for enumerating all vertices of the partition polytope. Our adjacency characterization also implies a polynomial upper bound on the combinatorial diameter of partition polytopes. We also establish a partition polytope analogue of the lower bound theorem, indicating that the output-sensitive enumeration algorithm can be far superior to previously known algorithms that run in time polynomial in the size of the worst-case output.     

Extensions of dually bipartite regular polytopes

This paper addresses the problem of finding abstract regular polytopes with preassigned facets and preassigned last entry of the Schläfli symbol. Using C-group permutation representation (CPR) graphs we give a solution to this problem for dually bipartite regular polytopes when the last entry of the Schläfli symbol is even. This construction is related to a previous construction by Schulte that solves the problem when the entry of the Schläfli symbol is 6.     

Mean width of random polytopes in a reasonably smooth convex body

Let K be a convex body in and let X_n=(x₁,…,x_n) be a random sample of n independent points in K chosen according to the uniform distribution. The convex hull K_n of X_n is a random polytope in K, and we consider its mean width W(K_n). In this article, we assume that K has a rolling ball of radius >0. First, we extend the asymptotic formula for the expectation of W(K)−W(K_n) which was earlier known only in the case when ∂K has positive Gaussian curvature. In addition, we determine the order of magnitude of the variance of W(K_n), and prove the strong law of large numbers for W(K_n). We note that the strong law of large numbers for any quermassintegral of K was only known earlier for the case when ∂K has positive Gaussian curvature.     

Poincaré-Hopf inequalities

In this article the main theorem establishes the necessity and sufficiency of the Poincaré-Hopf inequalities in order for the Morse inequalities to hold. The convex hull of the collection of all Betti number vectors which satisfy the Morse inequalities for a pre-assigned index data determines a Morse polytope defined on the nonnegative orthant. Using results from network flow theory, a scheme is provided for constructing all possible Betti number vectors which satisfy the Morse inequalities for a pre-assigned index data. Geometrical properties of this polytope are described.