scholarly journals Diameters of Cocircuit Graphs of Oriented Matroids: An Update

10.37236/9653 ◽  
2021 ◽  
Vol 28 (4) ◽  
Author(s):  
Ilan Adler ◽  
Jesús A. De Loera ◽  
Steven Klee ◽  
Zhenyang Zhang
Keyword(s):  
Directed Graphs ◽  
Hyperplane Arrangements ◽  
Oriented Matroids ◽  
Low Rank ◽  
Oriented Matroid ◽  
Computer Search ◽  
Linear Programs ◽  
Large Computer ◽  
Positive Side ◽  
Point Configurations

Oriented matroids are combinatorial structures that generalize point configurations, vector configurations, hyperplane arrangements, polyhedra, linear programs, and directed graphs. Oriented matroids have played a key  role in combinatorics, computational geometry, and optimization. This paper surveys prior work and presents an update on the search for bounds on the diameter of the cocircuit graph of an oriented matroid. The motivation for our investigations is the complexity of the simplex method and the criss-cross method. We review the diameter problem and show the diameter bounds of general oriented matroids reduce to those of uniform oriented matroids. We give the latest exact bounds for oriented matroids of low rank and low corank, and for all oriented matroids with up to nine elements (this part required a large computer-based proof).  For arbitrary oriented matroids, we present an improvement to a quadratic bound of Finschi. Our discussion highlights an old conjecture that states a linear bound for the diameter is possible. On the positive side, we show the conjecture is true for oriented matroids of low rank and low corank, and, verified with computers, for all oriented matroids with up to nine elements. On the negative side, our computer search showed two natural strengthenings of the main conjecture are false. 

scholarly journals Cell complexes, poset topology and the representation theory of algebras arising in algebraic combinatorics and discrete geometry

2021 ◽  
Vol 274 (1345) ◽  
Author(s):  
Stuart Margolis ◽  
Franco Saliola ◽  
Benjamin Steinberg
Keyword(s):  
Representation Theory ◽  
Hyperplane Arrangements ◽  
Oriented Matroids ◽  
Oriented Matroid ◽  
Regular Band ◽  
Left Regular ◽  
The Face ◽  
Left Regular Band ◽  
Poset Topology ◽  
Left Regular Bands

In recent years it has been noted that a number of combinatorial structures such as real and complex hyperplane arrangements, interval greedoids, matroids and oriented matroids have the structure of a finite monoid called a left regular band. Random walks on the monoid model a number of interesting Markov chains such as the Tsetlin library and riffle shuffle. The representation theory of left regular bands then comes into play and has had a major influence on both the combinatorics and the probability theory associated to such structures. In a recent paper, the authors established a close connection between algebraic and combinatorial invariants of a left regular band by showing that certain homological invariants of the algebra of a left regular band coincide with the cohomology of order complexes of posets naturally associated to the left regular band. The purpose of the present monograph is to further develop and deepen the connection between left regular bands and poset topology. This allows us to compute finite projective resolutions of all simple modules of unital left regular band algebras over fields and much more. In the process, we are led to define the class of CW left regular bands as the class of left regular bands whose associated posets are the face posets of regular CW complexes. Most of the examples that have arisen in the literature belong to this class. A new and important class of examples is a left regular band structure on the face poset of a CAT(0) cube complex. Also, the recently introduced notion of a COM (complex of oriented matroids or conditional oriented matroid) fits nicely into our setting and includes CAT(0) cube complexes and certain more general CAT(0) zonotopal complexes. A fairly complete picture of the representation theory for CW left regular bands is obtained.

scholarly journals Resurgences for ideals of special point configurations in PN coming from hyperplane arrangements

2015 ◽  
Vol 443 ◽  
pp. 383-394 ◽  
Author(s):  
M. Dumnicki ◽  
B. Harbourne ◽  
U. Nagel ◽  
A. Seceleanu ◽  
T. Szemberg ◽  
...  
Keyword(s):  
Hyperplane Arrangements ◽  
Special Point ◽  
Point Configurations

scholarly journals Face monoid actions and tropical hyperplane arrangements

2017 ◽  
Vol 27 (08) ◽  
pp. 1001-1025
Author(s):  
Marianne Johnson ◽  
Mark Kambites
Keyword(s):  
Hyperplane Arrangement ◽  
Hyperplane Arrangements ◽  
Oriented Matroid ◽  
Definition Of ◽  
The Way

We study the combinatorics of tropical hyperplane arrangements, and their relationship to (classical) hyperplane face monoids. We show that the refinement operation on the faces of a tropical hyperplane arrangement, introduced by Ardila and Develin in their definition of a tropical oriented matroid, induces an action of the hyperplane face monoid of the classical braid arrangement on the arrangement, and hence on a number of interesting related structures. Along the way, we introduce a new characterization of the types (in the sense of Develin and Sturmfels) of points with respect to a tropical hyperplane arrangement, in terms of partial bijections which attain permanents of submatrices of a matrix which naturally encodes the arrangement.

scholarly journals Triangulations of $\Delta_{n-1} \times \Delta_{d-1}$ and Tropical Oriented Matroids

2011 ◽  
Vol DMTCS Proceedings vol. AO,... (Proceedings) ◽  
Author(s):  
Suho Oh ◽  
Hwanchul Yoo
Keyword(s):  
Oriented Matroids ◽  
Oriented Matroid ◽  
Nous Proposons ◽  
Combinatorial Objects ◽  
New Class ◽  
Nous Montrons ◽  
International Audience ◽  
Tropical Polytopes

International audience Develin and Sturmfels showed that regular triangulations of $\Delta_{n-1} \times \Delta_{d-1}$ can be thought of as tropical polytopes. Tropical oriented matroids were defined by Ardila and Develin, and were conjectured to be in bijection with all subdivisions of $\Delta_{n-1} \times \Delta_{d-1}$. In this paper, we show that any triangulation of $\Delta_{n-1} \times \Delta_{d-1}$ encodes a tropical oriented matroid. We also suggest a new class of combinatorial objects that may describe all subdivisions of a bigger class of polytopes. Develin et Sturmfels ont montré que les triangulations de $\Delta_{n-1} \times \Delta_{d-1}$ peuvent être considérées comme des polytopes tropicaux. Les matroïdes orientés tropicaux ont été définis par Ardila et Develin, et ils ont été conjecturés être en bijection avec les subdivisions de $\Delta_{n-1} \times \Delta_{d-1}$. Dans cet article, nous montrons que toute triangulation de $\Delta_{n-1} \times \Delta_{d-1}$ encode un matroïde orienté tropical. De plus, nous proposons une nouvelle classe d'objets combinatoires qui peuvent décrire toutes les subdivisions d'une plus grande classe de polytopes.

scholarly journals Congruence Normality of Simplicial Hyperplane Arrangements via Oriented Matroids

2021 ◽  
Author(s):  
Michael Cuntz ◽  
Sophia Elia ◽  
Jean-Philippe Labbé
Keyword(s):  
Hyperplane Arrangements ◽  
Oriented Matroids ◽  
Weak Order ◽  
Polyhedral Cones ◽  
Normal Lattice ◽  
Poset Of Regions

AbstractA catalogue of simplicial hyperplane arrangements was first given by Grünbaum in 1971. These arrangements naturally generalize finite Coxeter arrangements and also the weak order through the poset of regions. The weak order is known to be a congruence normal lattice, and congruence normality of lattices of regions of simplicial arrangements can be determined using polyhedral cones called shards. In this article, we update Grünbaum’s catalogue by providing normals realizing all known simplicial arrangements with up to 37 lines and key invariants. Then we add structure to this catalogue by determining which arrangements always/sometimes/never lead to congruence normal lattices of regions. To this end, we use oriented matroids to recast shards as covectors to determine congruence normality of large hyperplane arrangements. We also show that lattices of regions coming from finite Weyl groupoids of any rank are always congruence normal.

Oriented Matroids

10.37236/25 ◽  
2002 ◽  
Vol 1000 ◽  
Author(s):  
Günter M. Ziegler
Keyword(s):  
Oriented Matroids ◽  
Entry Point ◽  
Oriented Matroid ◽  
Matroid Theory

This dynamic survey offers an “entry point” for current research in oriented matroids. For this, it provides updates on the 1993 monograph “Oriented Matroids” by Bjö̈rner, Las Vergnas, Sturmfels, White & Ziegler [85], in three parts: 1. a sketch of a few “Frontiers of Research” in oriented matroid theory, 2. an update of corrections, comments and progress as compared to [85], and 3. an extensive, complete and up-to-date bibliography of oriented matroids, comprising and extending the bibliography of [85].

scholarly journals Tropical hyperplane arrangements and oriented matroids

2008 ◽  
Vol 262 (4) ◽  
pp. 795-816 ◽  
Author(s):  
Federico Ardila ◽  
Mike Develin
Keyword(s):  
Hyperplane Arrangements ◽  
Oriented Matroids

scholarly journals On a Conjecture Concerning Dyadic Oriented Matroids

10.37236/1455 ◽  
1999 ◽  
Vol 6 (1) ◽  
Author(s):  
Matt Scobee
Keyword(s):  
Oriented Matroids ◽  
Oriented Matroid ◽  
Rational Matrix ◽  
Dyadic Representation ◽  
The Relationship

A rational matrix is totally dyadic if all of its nonzero subdeterminants are in $\{\pm 2^k\ :\ k \in {\bf Z}\}$. An oriented matriod is dyadic if it has a totally dyadic representation $A$. A dyadic oriented matriod is dyadic of order $k$ if it has a totally dyadic representation $A$ with full row rank and with the property that for each pair of adjacent bases $A_1$ and $A_2$ $$2^{-k} \le \left| { {\det(A_1)} \over {\det(A_2)}}\right|\le 2^k.$$ In this note we present a counterexample to a conjecture on the relationship between the order of a dyadic oriented matroid and the ratio of agreement to disagreement in sign of its signed circuits and cocircuits (Conjecture 5.2, Lee (1990)).

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