Title: Graph coloring of graphs with large girth is hard for the NullstellensatzSpeaker: Julián Romero Affiliation: University of Waterloo Zoom: Contact Sharat Ibrahimpur
In this talk we will discuss a method to solve combinatorial problems using hierarchies of systems of linear equations using Hilbert's Nullstellensatz. In particular, we will study the behaviour of these hierarchies for deciding the non-$k$-colorabilty of graphs.
Title: Sandpiles and representation theorySpeaker: Victor Reiner Affiliation: University of Minnesota Zoom: Contact Karen Yeats
For an undirected graph, its sandpile group is an interesting isomorphism invariant-- it is a finite abelian group that describes the integer cokernel of the graph's Laplacian matrix.