## Combinatorics and Graph Theory

•  Bruce Sagan, Michigan State University
•  Roots of descent polynomials
•  09/19/2017
•  4:10 PM - 5:00 PM
•  C304 Wells Hall

Let S_n be the symmetric group of all permutations p = p_1 ... p_n of the numbers 1, ..., n. The descent set of p is the set of indices i such that p_i > p_{i+1}. Given a set of positive integers I we let d(I;n) be the number of permutations in S_n with descent set I. In 1915 MacMahon proved that d(I;n) is a polynomial in n, but its properties do not seem to have been much studied until now. We apply the method of Newton bases from the previous lecture to make progress on a conjecture about the location of the roots of d(I;n) where n is now a complex number. This is joint work with Alexander Diaz-Lopez, Pamela Harris, Erik Insko, and Mohamed Omar.

## Contact

Department of Mathematics
Michigan State University