## Monday March 28, 2005, 4 PM, Goldsmith 317

### tea at
3:30 PM at the Math Department lounge (Goldsmith 300)

**Speaker**: Mark Skandera (Dartmouth College)

**Title**: Interpretations of totally nonnegative polynomials

**Abstract**:
A matrix is called totally nonnegative (TNN) if each of its square submatrices has a nonnegative determinant.

First seriously studied in the 1930s, TNN matrices appeared in the areas of differential equations and rational functions.

In the 1950s, Karlin and MacGregor proved a probabilistic result, which gave a very interesting interpretation of all TNN matrices. This interpretation led to more applications in combinatorics, algebra, electrical engineering, and chemistry.

Recent work in physics and Lie theory has led to a generalization of the classical definitions, and in particular to the study of functions called totally nonnegative polynomials and Schur nonnegative polynomials. We will present a new result concerning these polynomials and will discuss how it was
used in February to prove conjectures of Fomin, Lascoux, Okounkov and others.

This talk will be accessible to undergraduates.