Results 1  10
of
24
The Polytope of All Triangulations of a Point Configuration
, 1996
"... We study the convex hull PA of the 01 incidence vectors of all triangulations of a point configuration A. This was called the universal polytope in [4]. The affine span of PA is described in terms of the cocircuits of the oriented matroid of A. Its intersection with the positive orthant is a quasi ..."
Abstract

Cited by 47 (25 self)
 Add to MetaCart
We study the convex hull PA of the 01 incidence vectors of all triangulations of a point configuration A. This was called the universal polytope in [4]. The affine span of PA is described in terms of the cocircuits of the oriented matroid of A. Its intersection with the positive orthant is a quasiintegral polytope QA whose integral hull equals PA . We present the smallest example where QA and PA differ. The duality theory for regular triangulations in [5] is extended to cover all triangulations. We discuss potential applications to enumeration and optimization problems regarding all triangulations.
TOPCOM: TRIANGULATIONS OF POINT CONFIGURATIONS AND ORIENTED MATROIDS
, 2002
"... TOPCOM is a package for computing triangulations of point configurations and oriented matroids. For example, for a point configuration one can compute the chirotope, components of the flip graph of triangulations, enumerate all triangulations. The core algorithms implemented in TOPCOM are described ..."
Abstract

Cited by 32 (1 self)
 Add to MetaCart
TOPCOM is a package for computing triangulations of point configurations and oriented matroids. For example, for a point configuration one can compute the chirotope, components of the flip graph of triangulations, enumerate all triangulations. The core algorithms implemented in TOPCOM are described, and implentation issues are discussed.
The Cayley Trick, Lifting Subdivisions And The BohneDress Theorem On Zonotopal Tilings
 J. EUR. MATH. SOC
, 1999
"... In 1994, Sturmfels gave a polyhedral version of the Cayley Trick of elimination theory: he established an orderpreserving bijection between the posets of coherent mixed subdivisions of a Minkowski sum A 1 + \Delta \Delta \Delta +A r of point configurations and of coherent polyhedral subdivisions o ..."
Abstract

Cited by 31 (13 self)
 Add to MetaCart
In 1994, Sturmfels gave a polyhedral version of the Cayley Trick of elimination theory: he established an orderpreserving bijection between the posets of coherent mixed subdivisions of a Minkowski sum A 1 + \Delta \Delta \Delta +A r of point configurations and of coherent polyhedral subdivisions of the associated Cayley embedding C (A 1 ; : : : ; A r ). In this paper we extend this correspondence in a natural way to cover also noncoherent subdivisions. As an application, we show that the Cayley Trick combined with results of Santos on subdivisions of Lawrence polytopes provides a new independent proof of the BohneDress Theorem on zonotopal tilings. This application uses a combinatorial characterization of lifting subdivisions, also originally proved by Santos.
The Cayley Trick and triangulations of products of simplices
 in “Proceedings of the Joint Summer Research Conference on Integer Points in Polyhedra. Geometry, Number Theory, Algebra, and Optimization
"... Abstract. We use the Cayley Trick to study polyhedral subdivisions of the product of two simplices. For arbitrary (fixed) l ≥ 2, we show that the numbers of regular and nonregular triangulations of ∆ l × ∆ k grow, respectively, as k Θ(k) and 2 Ω(k2). For the special case of ∆ 2 × ∆ k, we relate t ..."
Abstract

Cited by 22 (1 self)
 Add to MetaCart
Abstract. We use the Cayley Trick to study polyhedral subdivisions of the product of two simplices. For arbitrary (fixed) l ≥ 2, we show that the numbers of regular and nonregular triangulations of ∆ l × ∆ k grow, respectively, as k Θ(k) and 2 Ω(k2). For the special case of ∆ 2 × ∆ k, we relate triangulations to certain class of lozenge tilings. This allows us to compute the exact number of triangulations up to k = 15, show that the number grows as e βk2 /2+o(k 2) where β ≃ 0.32309594 and prove that the set of all triangulations is connected under geometric bistellar flips. The latter has as a corollary that the toric Hilbert scheme of the determinantal ideal of 2×2 minors of a 3×k matrix is connected, for every k. We include “Cayley Trick pictures ” of all the triangulations of ∆ 2 × ∆ 2 and ∆ 2 × ∆ 3, as well as one nonregular triangulation of ∆ 2 × ∆ 5 and another of ∆ 3 × ∆ 3.
The number of geometric bistellar neighbors of a triangulation
 Geom
, 1999
"... The theory of secondary and fiber polytopes implies that regular (also called convex or coherent) triangulations of configurations with n points in R ..."
Abstract

Cited by 18 (8 self)
 Add to MetaCart
The theory of secondary and fiber polytopes implies that regular (also called convex or coherent) triangulations of configurations with n points in R
The generalized Baues problem
, 1998
"... Abstract. We survey the generalized Baues problem of Billera and Sturmfels. The problem is one of discrete geometry and topology, and asks about the topology of the set of subdivisions of a certain kind of a convex polytope. Along with a discussion of most of the known results, we survey the motivat ..."
Abstract

Cited by 17 (0 self)
 Add to MetaCart
Abstract. We survey the generalized Baues problem of Billera and Sturmfels. The problem is one of discrete geometry and topology, and asks about the topology of the set of subdivisions of a certain kind of a convex polytope. Along with a discussion of most of the known results, we survey the motivation for the problem and its relation to triangulations, zonotopal tilings, monotone paths in linear programming, oriented matroid Grassmannians, singularities, and homotopy theory. Included are several open questions and problems. 1.
Tropical hyperplane arrangements and oriented matroids
 Math. Zeitschrift
"... Abstract. We study the combinatorial properties of a tropical hyperplane arrangement. We define tropical oriented matroids, and prove that they share many of the properties of ordinary oriented matroids. We show that a tropical oriented matroid determines a subdivision of a product of two simplices, ..."
Abstract

Cited by 11 (0 self)
 Add to MetaCart
Abstract. We study the combinatorial properties of a tropical hyperplane arrangement. We define tropical oriented matroids, and prove that they share many of the properties of ordinary oriented matroids. We show that a tropical oriented matroid determines a subdivision of a product of two simplices, and conjecture that this correspondence is a bijection. 1.
Computational approaches to lattice packing and covering problems
 Discrete Comput. Geom. 35 (2006) 73–116. MR2183491 (2006k:52048
"... We describe algorithms which solve two classical problems in lattice geometry for any fixed dimension d: the lattice covering and the simultaneous lattice packing–covering problem. Both algorithms involve semidefinite programming and are based on Voronoi’s reduction theory for positive definite quad ..."
Abstract

Cited by 10 (6 self)
 Add to MetaCart
We describe algorithms which solve two classical problems in lattice geometry for any fixed dimension d: the lattice covering and the simultaneous lattice packing–covering problem. Both algorithms involve semidefinite programming and are based on Voronoi’s reduction theory for positive definite quadratic forms which describes all possible Delone triangulations of Z d. Our implementations verify all known results in dimensions d ≤ 5. Beyond that we attain complete lists of all locally optimal solutions for d = 5. For d = 6 our computations produce new best known covering as well as packing–covering
Fiber Polytopes For The Projections Between Cyclic Polytopes
, 1997
"... The cyclic polytope C(n; d) is the convex hull of any n points on the moment curve f(t; t 2 ; : : : ; t d ) : t 2 Rg in R d . For d 0 ? d, we consider the fiber polytope (in the sense of Billera and Sturmfels) associated to the natural projection of cyclic polytopes : C(n; d 0 ) ! C(n; ..."
Abstract

Cited by 9 (9 self)
 Add to MetaCart
The cyclic polytope C(n; d) is the convex hull of any n points on the moment curve f(t; t 2 ; : : : ; t d ) : t 2 Rg in R d . For d 0 ? d, we consider the fiber polytope (in the sense of Billera and Sturmfels) associated to the natural projection of cyclic polytopes : C(n; d 0 ) ! C(n; d) which "forgets" the last d 0 \Gamma d coordinates. It is known that this fiber polytope has face lattice indexed by the coherent polytopal subdivisions of C(n; d) which are induced by the map . Our main result characterizes the triples (n; d; d 0 ) for which the fiber polytope is canonical in either of the following two senses: ffl all polytopal subdivisions induced by are coherent, ffl the structure of the fiber polytope does not depend upon the choice of points on the moment curve. We also discuss a new instance with a positive answer to the Generalized Baues Problem, namely that of a projection : P ! Q where Q has only regular subdivisions and P has two more vertices than its...
Triangulations With Very Few Geometric Bistellar Neighbors
 Discrete Comput. Geom
, 1998
"... We are interested in a notion of elementary change between triangulations of a point configuration, the socalled bistellar flips, introduced by Gel'fand, Kapranov and Zelevinski. We construct sequences of triangulations of point configurations in dimension 3 with n 2 +2n+2 vertices and only 4n \G ..."
Abstract

Cited by 9 (3 self)
 Add to MetaCart
We are interested in a notion of elementary change between triangulations of a point configuration, the socalled bistellar flips, introduced by Gel'fand, Kapranov and Zelevinski. We construct sequences of triangulations of point configurations in dimension 3 with n 2 +2n+2 vertices and only 4n \Gamma 3 geometric bistellar flips (for every even integer n), and of point configurations in dimension 4 with arbitrarily many vertices and a bounded number of flips. This drastically improves previous examples and seems to be evidence against the conjecture that any two triangulations of a point configuration can be joined by a sequence of flips. Introduction Given a finite point configuration A in the Euclidean space R d of dimension d we call triangulations of A all the geometrically realized simplicial complexes which cover the convex hull of A and which have their sets of vertices contained in A. In this paper we are interested in a notion of vicinity or elementary change between tri...