For any k \times n matrix, the collection of k-element subsets of columns which are linearly independent forms a matroid. Linear independence of columns is, of course, equivalent to non-vanishing of the corresponding determinant, or "maximal minor." If we impose the additional condition that all non-zero maximal minors are positive, then we get a special kind of matroid--a positroid!

In this talk, I will show how positroids are indexed by Postnikov's "Le Diagrams," and I will explain how to use planar networks to generate all the matrices corresponding to a given positroid. I will try to indicate some of the reasons why positroids are such a nice class of matroids. Speaker(s): Gabriel Frieden (University of Michigan)