Mon, May 4 3pm ET (8pm BST, 7am Tue NZST)
Nathan Bowler, Universität Hamburg
I’ll talk about a couple of classes of matroids which sit between frame and lifted-graphic matroids: the biased graphic matroids, which sit between these classes in a sense introduced by Zaslavsky, and the slightly better behaved quasi-graphic matroids, which were recently introduced by Geelen, Gerards and Whittle. I’ll give a very concrete combinatorial descriptions of the quasi-graphic matroids and use this to derive a fairly clean characterisation of the biased graphic matroids. I’ll discuss a topological construction giving some nontrivial examples of quasi-graphic matroids and raise the question of whether most examples are constructed in essentially this way.