## 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

Thursday, July 16, 2020 — 2:30 PM EDT

## Algebraic Combinatorics Seminar - Oliver Pechenik

Title: Dynamics of plane partitions

 Speaker: Oliver Pechenik Affiliation: University of Waterloo Zoom: Contact Karen Yeats

Abstract:

Consider a plane partition P in an a X b X c box. The rowmotion operator sends P to the plane partition generated by the minimal elements of its complement. We show rowmotion resonates with frequency a+b+c-1, in the sense that each orbit size shares a prime divisor with a+b+c-1. This confirms a 1995 conjecture of Peter Cameron and Dmitri Fon-Der-Flaass. (Based on joint works with Kevin Dilks & Jessica Striker and with Becky Patrias.)

Friday, July 17, 2020 — 1:30 PM EDT

Title: Two unsolved problems: Birkhoff--von Neumann graphs and PM-compact graphs

 Speaker: Nishad Kothari Affiliation: CSE Department, Indian Institute of Technology Madras Zoom: Contact Sharat Ibrahimpur

Abstract:

A well-studied object in combinatorial optimization is the {\it perfect matching polytope} $\mathcal{PMP}(G)$ of a graph $G$ --- the convex hull of the incidence vectors of all perfect matchings of $G$. A graph $G$ is {\it Birkhoff--von Neumann} if $\mathcal{PMP}(G)$ is characterized solely by non-negativity and degree constraints, and $G$ is {\it PM-compact} if the combinatorial diameter of $\mathcal{PMP}(G)$ equals one.

Friday, July 17, 2020 — 3:30 PM EDT

## Tutte Colloquium - Shachar Lovett

Title: Point Location and Active Learning - Learning Halfspaces Almost Optimally

 Speaker: Shachar Lovett Affiliation: UC San Diego Zoom: Please email Emma Watson

Abstract:

The point location problem is a central problem in computational geometry. It asks, given a known partition of R^d by n hyperplanes, and an unknown input point, to find the cell in the partition to which the input point belongs. The access to the input is via linear queries. A linear query is specified by an hyperplane, and the result of the query is which side of the hyperplane the input point lies in.

Monday, July 20, 2020 — 11:30 AM EDT

## Algebraic Graph Theory Seminar - Karen Meagher

Title: Group Theory and the Erd\H{o}s-Ko-Rado (EKR) Theorem

 Speaker: Karen Meagher Affiliation: University of Regina Zoom: Contact Soffia Arnadottir

Abstract:

Group theory can be a key tool in sovling problems in combinatorics; it can provide a clean and effective proofs, and it can give deeper understanding of why certain combinatorial results hold. My research has focused on the famous Erd\H{o}s-Ko-Rado (EKR) theorem.

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