Contact Info
Combinatorics & Optimization
University of Waterloo
Waterloo, Ontario
Canada N2L 3G1
Phone: 519-888-4567, ext 33038
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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
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.