## University COVID-19 update

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

# Events - July 2019

Friday, July 26, 2019 — 1:00 PM EDT

## Combinatorial Optimization Reading Group - Justin Toth

Title: New and Simple Algorithms for Stable Flow Problems

 Speaker: Justin Toth Affiliation: University of Waterloo Room: MC 5479

Abstract:

In the previous reading group talk we defined stable flows and saw that they always exist by a reduction to the stable allocation problem.

Thursday, July 25, 2019 — 3:30 PM EDT

## Algebraic Combinatorics Seminar - Melanie Dennis

Title: Lewis Carroll and the Red Hot Potato

 Speaker: Melanie Dennis Affiliation: Dartmouth College Room: MC 5417

Abstract:

The Lewis Carroll identity expresses the determinant of a matrix in terms of subdeterminants obtained by deleting one row and column or a pair of rows and columns.

Thursday, July 25, 2019 — 2:30 PM EDT

## Algebraic Graph Theory Seminar - Steve Kirkland

Title: Kemeny's Constant for Markov Chains

 Speaker: Steve Kirkland Affiliation: University of Manitoba Room: MC 5479

Abstract:

Markov chains are a much-studied class of stochastic processes, and it is well-known that if the transition matrix A associated with a Markov chain possesses a certain property (called primitivity), then the long-term behaviour of the Markov chain is described by a particular eigenvector of A, known as the stationary distribution vector.

Wednesday, July 24, 2019 — 4:30 PM EDT

## Joint C&O/PureMath Colloquium - Soffia Arnadottir

Title: Graphs in algebra and algebra in graphs

 Speaker: Soffia Arnadottir Affiliation: University of Waterloo Room: MC 5501

Abstract:

How do algebraic properties of a graph relate to its graph theoretic properties? What are algebraic properties of graphs? What does the spectrum of a graph tell us about its structure? What is a Cayley graph?

Tuesday, July 23, 2019 — 3:30 PM EDT

## Algebraic Combinatorics Seminar - Hugh Thomas

Title: Reverse plane partitions via quiver representations

 Speaker: Hugh Thomas Affiliation: Université du Québec à Montréal Room: MC 5417

Abstract:

Let $\lambda$ be a partition. The reverse plane partitions of shape $\lambda$ are a kind of filling of the Ferrers diagram of $\lambda$ by non-negative integers. Richard Stanley found the generating function which enumerates them according to the sum of the entries.

Friday, July 19, 2019 — 3:30 PM EDT

## Tutte Distinguished Lecture - Mario Szegedy

Title: QAOA Versus Classical

 Speaker: Mario Szegedy Affiliation: Alibaba Quantum Laboratory Room: MC 5501

Abstract:

There has been a back and forth about whether the QAOA algorithm of Farhi, Goldstone and Gutmann can in some sense be duplicated classically.

Friday, July 19, 2019 — 1:00 PM EDT

## Combinatorial Optimization Reading Group - Sharat Ibrahimpur

Title: Stable Flows

 Speaker: Sharat Ibrahimpur Affiliation: University of Waterloo Room: MC 5479

Abstract:

We describe a flow model that generalizes ordinary network flows the same way as stable matchings generalize the bipartite matching problem.

Thursday, July 18, 2019 — 3:30 PM EDT

## Algebraic Combinatorics Seminar - Lucia Rotheray

Title: Incidence bialgebras of monoidal categories

 Speaker: Lucia Rotheray Affiliation: Technische Universität Dresden Room: MC 5417

Abstract:

We begin with Joni and Rota's definition of the incidence coalgebra of a category or partially ordered set and then discuss some cases where a monoidal product on a category turns this coalgebra into a bialgebra.

Tuesday, July 16, 2019 — 3:30 PM EDT

## Algebraic Combinatorics Seminar - Stephen Melczer

Title: From Combinatorics to Computer Algebra and Morse Theory - Making Sense of Multivariate Asymptotics

 Speaker: Stephen Melczer Affiliation: University of Pennsylvania Room: MC 5479

Abstract:

The  asymptotic study  of  multivariate  generating  functions comprises  the  domain  of  Analytic Combinatorics  in Several Variables (ACSV).

Friday, July 12, 2019 — 3:30 PM EDT

## Tutte Colloquium - Kanstantsin Pashkovich

Title: On the approximability of the stable matching problem with ties of size two and one-sided ties

 Speaker: Kanstantsin Pashkovich Affiliation: University of Ottawa Room: MC 5501

Abstract:

The stable matching problem is central for game theory. If participants are allowed to have ties, the problem of finding a stable matching of maximum cardinality is an NP-hard problem, even when the ties are of size two.

Friday, July 12, 2019 — 1:00 PM EDT

Title: A (1 + 1/e)-Approximation Algorithm for Maximum Stable Matching with One-Sided Ties and Incomplete Lists

 Speaker: Madison Van Dyk Affiliation: University of Waterloo Room: MC 5479

Abstract:

We will continue the discussion of stable matching when there are unacceptable pairs and one-sided ties. Two weeks ago, we looked at a 3/2-approximation that was purely combinatorial.

Thursday, July 11, 2019 — 3:30 PM EDT

## Algebraic Combinatorics - William Slofstra

Title: Indicence groups of graphs, forbidden minors, and planar covers

 Speaker: William Slofstra Affiliation: University of Waterloo Room: MC 5417

Abstract:

The solution group of binary linear system is a quantum-probabilistic generalization of the solution space of the system.

Friday, July 5, 2019 — 3:03 PM EDT

## Tutte Colloquium - Karen Yeats

Title: Feynman graphs to chord diagrams

 Speaker: Karen Yeats Affiliation: University of Waterloo Room: MC 5501

Abstract:

I will explain how classic techniques of algebraic combinatorics can, via chord diagrams, tell us about the leading log, next-to-leading log, etc, expansions in quantum field theory, and what we think chord diagrams can tell us about individual Feynman graphs as well.

Friday, July 5, 2019 — 1:00 PM EDT

## Combinatorial Optimization Reading Group - Kanstantsin Pashkovich

Title: Quasi-popular Matchings, Optimality, and Extended Formulations

 Speaker: Kanstantsin Pashkovich Affiliation: University of Waterloo Room: MC 5479

Abstract:

The goal of this talk is to obtain efficient algorithms for computing desirable matchings (wrt cost) by paying the price of mildly relaxing popularity.

Thursday, July 4, 2019 — 3:30 PM EDT

## Algebraic Combinatorics - Angele Hamel

Title: Fun with Pfaffians: Identities for Schur Q-Functions

 Speaker: Angele Hamel Affiliation: Wilfrid Laurier University Room: MC 5417

Abstract:

Schur functions determinantal identities (e.g. Jacobi-Trudi, Giambelli) are cornerstones of symmetric function theory. Less well-known are the Pfaffian identities for Schur Q-functions.

Thursday, July 4, 2019 — 2:30 PM EDT

## Algebraic Graph Theory Seminar - Chris Godsil

Title: Mutually unbiased bases

 Speaker: Chris Godsil Affiliation: University of Waterloo Room: MC 5479

Abstract:

A pair of d x d unitary matrices is unbiased if M*N is at, i.e., all its entries have the same absolute value. A relatively simple argument shows that a set of pairwise unbiased unitary matrices has size at most d + 1.

Tuesday, July 2, 2019 — 4:00 PM EDT

## Graphs and Matroids Seminar - Kevin Grace

Title: Dyadic matroids with spanning cliques

 Speaker: Kevin Grace Affiliation: University of Bristol Room: MC 5479

*Please note time and date change

Abstract:

The Matroid Minors Project of Geelen, Gerards, and Whittle describes the structure of minor-closed classes of matroids representable over a fixed finite field.

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