The structure of matroids with a spanning clique or projective geometry

Abstract

Let $s,n\ge 2$ be integers. We give a qualitative structural description of every matroid $M$ that is spanned by a frame matroid of a complete graph and has no $U_{s,2s}$-minor and no rank-$n$ projective geometry minor, showing that every such matroid is `close' to a frame matroid. We also give a similar description of every matroid $M$ with a spanning projective geometry over a field GF$(q)$ as a restriction and with no $U_{s,2s}$-minor and no PG$(n,q^{\prime })$-minor for any $q^{\prime }>q$, showing that such an $M$ is `close' to a GF$(q)$-representable matroid.