Representations of Bicircular Lift Matroids

Bicircular lift matroids are a class of matroids defined on the edge set of a graph. For a given graph G, the circuits of its bicircular lift matroid are the edge sets of those subgraphs of G that contain at least two cycles, and are minimal with respect to this property. The main result of this paper is a characterization of when two graphs give rise to the same bicircular lift matroid, which answers a question proposed by Irene Pivotto. In particular, aside from some appropriately defined “small” graphs, two graphs have the same bicircular lift matroid if and only if they are 2-isomorphic in the sense of Whitney.