Abstracts for the Seminar
 Discrete Geometry and Combinatorics
 Fall 2014

Speaker:  Puck Rombach, UCLA
Title: Planar graphs represent all positroid strata
Time: 2:30 PM, Monday, December 1, 2014
Place:  Malott 206

Abstract: The positroid stratification, studied by many authors, is a coarsening of the matroid stratification of the Grassmannian. Each graph (with orientation and edge-ordering) gives a point in the Grassmannian; for a matroid stratum to contain such a point is a well-known forbidden minor condition on the matroid. We show that, by contrast, every positroid stratum contains a graphical representative; indeed, one can choose the graph to be planar. Joint work with Allen Knutson. The talk should be understandable with an elementary knowledge of graph theory.