Events - July 2019

Friday, July 26, 2019 — 1:00 PM EDT

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

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

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

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

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

Mario Szegedy headshot

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

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

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

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

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

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

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

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

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

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

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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