DECOMPOSITION OF BINARY SIGNED-GRAPHIC MATROIDS

In this paper we employ Tutte's theory of bridges to derive a decomposition theorem for binary matroids arising from signed graphs. The proposed decomposition differs from previous decomposition results on matroids that have appeared in the literature in the sense that it is not based on k-sums but rather on the operation of deletion of a cocircuit. Specifically, it is shown that certain minors resulting from the deletion of a cocircuit of a binary matroid will be graphic matroids, apart from exactly one that will be signed-graphic, if and only if the matroid is signed-graphic.