3 research outputs found
Quadratically Dense Matroids
This thesis is concerned with finding the maximum density of rank- matroids in a minor-closed class.
The extremal function of a non-empty minor-closed class of matroids which excludes a rank-2 uniform matroid is defined by
The Growth Rate Theorem of Geelen, Kabell, Kung, and Whittle shows that this function is either linear, quadratic, or exponential in .
In this thesis we prove a general result about classes with quadratic extremal function, and then use it to determine the extremal function for several interesting classes of representable matroids, for sufficiently large integers .
In particular, for each integer we find the extremal function for all but finitely many for the class of -representable matroids with no -minor, and we find the extremal function for the class of matroids representable over finite fields and where divides and and are relatively prime