Hodge Theory in Combinatorics by Eric Katz

School of Mathematics Colloquium
Thursday, January 14, 2016 - 11:00
1 hour (actually 50 minutes)
Skiles 006
University of Waterloo
We discuss applications of Hodge theory which is a part of algebraic geometry to problems in combinatorics, in particular to Rota's Log-concavity Conjecture.  The conjecture was motivated by a question in enumerating proper colorings of a graph which are counted by the chromatic polynomial.  This polynomial's coefficients were conjectured to form a unimodal sequence by Read in 1968.  This conjecture was extended by Rota in his 1970 ICM address to assert the log-concavity of the characteristic polynomial of matroids which are the common combinatorial generalizations of graphs and linear subspaces.  We discuss the resolution of this conjecture which is joint work with Karim Adiprasito and June Huh. The solution draws on ideas from the theory of algebraic varieties, specifically Hodge theory, showing how a question about graph theory leads to a solution involving Grothendieck's standard conjectures.  This talk is a preview for the upcoming workshop at Georgia Tech.