I will talk about rational power series in several variables with nonnegative power series coefficients. An example of such a series is 1/(1-x-y-z+4xyz), whose power series coefficients were proved nonnegative by Szegő and Kaluza in 1933. I will discuss several methods for proving nonnegativity and also some conjectures.
CAGE: Philadelphia Area Combinatorics and Alg. Geometry Seminar
Thursday, April 5, 2018 - 3:00pm
Ira Gessel
Brandeis University