## University COVID-19 update

### Questions about buildings and services? Visit the list of Modified Services.

Please note: The University of Waterloo is closed for all events until further notice.

# Events by date

## Thursday, June 18, 2020

### Combinatorial Optimization Reading Group - Julián Romero

Thursday, June 18, 2020 — 1:03 PM EDT

Title: Graph coloring of graphs with large girth is hard for the Nullstellensatz

Speaker: Julián Romero Affiliation: University of Waterloo Zoom: Contact Sharat Ibrahimpur

Abstract:

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.

### Algebraic Combinatorics Seminar - Victor Reiner

Thursday, June 18, 2020 — 2:30 PM EDT

Title: Sandpiles and representation theory

Speaker: Victor Reiner Affiliation: University of Minnesota Zoom: Contact Karen Yeats

Abstract:

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.

### June 2020

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