A central problem in matroid theory—and by extension coding theory and finite geometry— is the problem of constructing matrices with a maximal number of columns such that every square submatrix formed by a subset of the columns is nonsingular. In this project, we apply the tools of analysis to this problem and demonstrate the value of such an approach. First, we introduce various quantities tha...

A nongraphic matroid M is said to be almost-graphic if, for all elements e, either M\e or M/e is graphic. We determine completely the class of almost-graphic matroids, thereby answering a question posed by Oxley in his book “Matroid Theory.” A nonregular matroid is said to be almost-regular if, for all elements e, either M\e or M/e is regular. An element e for which both M\e and M/e are regular...

Motivated by a question of Duval and Reiner about higher Laplacians of simplicial complexes, we describe various relaxations of the defining axioms of matroid theory to obtain larger classes of simplicial complexes that contain pure shifted simplicial complexes. The resulting classes retain some of the matroid properties and allow us to classify matroid properties according to the relevant axio...

We prove that for every proper minor-closed class M of Fp-representable matroids, there exists a O(1)-competitive algorithm for the matroid secretary problem on M. This result relies on the extremely powerful matroid minor structure theory being developed by Geelen, Gerards and Whittle. We also note that for asymptotically almost all matroids, the matroid secretary algorithm that selects a rand...

A fundamental theorem of matroid theory establishes that a transversal matroid is representable over fields of any characteristic. It was proved in 1970 by Piff and Welsh: their proof is elegant and concise and, moveover, constructive. However it is far from being algorithmic, in terms of suggesting a step-by-step procedure for deriving a collection of vectors over a given base field representi...

Bollobás and Riordan introduce a Tutte polynomial for coloured graphs and matroids in [3]. We observe that this polynomial has an expansion as a sum indexed by the subsets of the ground-set of a coloured matroid, generalizing the subset expansion of the Tutte polynomial. We also discuss similar expansions of other contraction–deletion invariants of graphs and matroids. 1. The coloured Tutte pol...

Extending work of Bielawski-Dancer [3] and Konno [12], we develop a theory of toric hyperkähler varieties, which involves toric geometry, matroid theory and convex polyhedra. The framework is a detailed study of semi-projective toric varieties, meaning GIT quotients of affine spaces by torus actions, and specifically, of Lawrence toric varieties, meaning GIT quotients of even-dimensional affine...

The weighted matroid intersection problem has recently been extended to the valuated matroid intersection problem: Given a pair of valuated matroids Mi = (V,Bi, ωi) (i = 1, 2) defined on a common ground set V , find a common base B ∈ B1∩B2 that maximizes ω1(B)+ω2(B). This paper develops a Fenchel-type duality theory related to this problem with a view to establishing a convexity framework for n...

Matroid theory was first formalized in 1935 by Whitney [5] who introduced the notion as an attempt to study the properties of vector spaces in an abstract manner. Since then, matroids have proven to have numerous applications in a wide variety of fields including combinatorics and graph theory. Today we will briefly survey matroid representation and then discuss some problems in matroid optimiz...