Extremal critically connected matroids

Generating weakly 4-connected matroids

We prove that, if M is a weakly 4-connected matroid with |E(M)| 7 and neither M nor M∗ is isomorphic to the cycle matroid of a ladder, then M has a proper minor M ′ such that M ′ is weakly 4-connected and |E(M ′)| |E(M)| − 2 unless M is some 12-element matroid with a special structure. © 2007 Elsevier Inc. All rights reserved.

On Nonbinary 3-connected Matroids

It is well known that a matroid is binary if and only if it has no minor isomorphic to U2,4, the 4-point line. Extending this result, Bixby proved that every element in a nonbinary connected matroid is in a U2,4minor. The result was further extended by Seymour who showed that every pair of elements in a nonbinary 3-connected matroid is in a U2,4-minor. This paper extends Seymour's theorem by pr...

On minor-minimally-connected matroids

Involutions Of Connected Binary Matroids

We prove that if an involution φ is an automorphism of a connected binary matroid M , then there is a hyperplane of M that is invariant under φ. We also consider extensions of this result for higher connectivity.

Mutual information, matroids and extremal dependencies

In this paper, it is shown that the rank function of a matroid can be represented by a “mutual information function” if and only if the matroid is binary. The mutual information function considered is the one measuring the amount of information between the inputs (binary uniform) and the output of a multiple access channel (MAC). Moreover, it is shown that a MAC whose mutual information functio...