375 research outputs found
A Characterization of Certain Excluded-Minor Classes of Matroids
A result of Walton and the author establishes that every 3-connected matroid of rank and corank at least three has one of five six-element rank-3 self-dual matroids as a minor. This paper characterizes two classes of matroids that arise when one excludes as minors three of these five matroids. One of these results extends the author\u27s characterization of the ternary matroids with no M(K4)-minor, while the other extends Tutte\u27s excluded-minor characterization of binary matroids. © 1989, Academic Press Limited. All rights reserved
On Binary And Regular Matroids Without Small Minors
The results of this dissertation consist of excluded-minor results for Binary Matroids and excluded-minor results for Regular Matroids. Structural theorems on the relationship between minors and k-sums of matroids are developed here in order to provide some of these characterizations. Chapter 2 of the dissertation contains excluded-minor results for Binary Matroids. The first main result of this dissertation is a characterization of the internally 4-connected binary matroids with no minor that is isomorphic to the cycle matroid of the prism+e graph. This characterization generalizes results of Mayhew and Royle [18] for binary matroids and results of Dirac [8] and Lovász [15] for graphs. The results of this chapter are then extended from the class of internally 4-connected matroids to the class of 3-connected matroids. Chapter 3 of the dissertation contains the second main result, a decomposition theorem for regular matroids without certain minors. This decomposition theorem is used to obtain excluded-minor results for Regular Matroids. Wagner, Lovász, Oxley, Ding, Liu, and others have characterized many classes of graphs that are H-free for graphs H with at most twelve edges (see [7]). We extend several of these excluded-minor characterizations to regular matroids in Chapter 3. We also provide characterizations of regular matroids excluding several graphic matroids such as the octahedron, cube, and the Möbius Ladder on eight vertices. Both theoretical and computer-aided proofs of the results of Chapters 2 and 3 are provided in this dissertation
Delta-matroids as subsystems of sequences of Higgs Lifts
In [30], Tardos studied special delta-matroids obtained from sequences of
Higgs lifts; these are the full Higgs lift delta-matroids that we treat and around which
all of our results revolve. We give an excluded-minor characterization of the class of
full Higgs lift delta-matroids within the class of all delta-matroids, and we give similar
characterizations of two other minor-closed classes of delta-matroids that we define using
Higgs lifts. We introduce a minor-closed, dual-closed class of Higgs lift delta-matroids
that arise from lattice paths. It follows from results of Bouchet that all delta-matroids can
be obtained from full Higgs lift delta-matroids by removing certain feasible sets; to address
which feasible sets can be removed, we give an excluded-minor characterization of deltamatroids
within the more general structure of set systems. Many of these excluded minors
occur again when we characterize the delta-matroids in which the collection of feasible
sets is the union of the collections of bases of matroids of different ranks, and yet again
when we require those matroids to have special properties, such as being paving
On two classes of nearly binary matroids
We give an excluded-minor characterization for the class of matroids M in
which M\e or M/e is binary for all e in E(M). This class is closely related to
the class of matroids in which every member is binary or can be obtained from a
binary matroid by relaxing a circuit-hyperplane. We also provide an
excluded-minor characterization for the second class.Comment: 14 pages, 4 figures. This paper has been accepted for publication in
the European Journal of Combinatorics. This is the final version of the pape
The Lattice of Cyclic Flats of a Matroid
A flat of a matroid is cyclic if it is a union of circuits. The cyclic flats
of a matroid form a lattice under inclusion. We study these lattices and
explore matroids from the perspective of cyclic flats. In particular, we show
that every lattice is isomorphic to the lattice of cyclic flats of a matroid.
We give a necessary and sufficient condition for a lattice Z of sets and a
function r on Z to be the lattice of cyclic flats of a matroid and the
restriction of the corresponding rank function to Z. We define cyclic width and
show that this concept gives rise to minor-closed, dual-closed classes of
matroids, two of which contain only transversal matroids.Comment: 15 pages, 1 figure. The new version addresses earlier work by Julie
Sims that the authors learned of after submitting the first versio
Splitters and Decomposers for Binary Matroids
Let denote the class of binary matroids with no minors
isomorphic to . In this paper we give a decomposition theorem
for , where is a certain 10-element rank-4
matroid. As corollaries we obtain decomposition theorems for the classes
obtained by excluding the Kuratowski graphs and . These decomposition
theorems imply results on internally -connected matroids by Zhou
[\ref{Zhou2004}], Qin and Zhou [\ref{Qin2004}], and Mayhew, Royle and Whitte
[\ref{Mayhewsubmitted}].Comment: arXiv admin note: text overlap with arXiv:1403.775
Matroids with nine elements
We describe the computation of a catalogue containing all matroids with up to
nine elements, and present some fundamental data arising from this cataogue.
Our computation confirms and extends the results obtained in the 1960s by
Blackburn, Crapo and Higgs. The matroids and associated data are stored in an
online database, and we give three short examples of the use of this database.Comment: 22 page
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