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Friday, January 31, 2020 1:00 pm - 1:00 pm EST (GMT -05:00)

Combinatorial Optimization Reading Group - Hong Zhou

Title: Network Design $s$-$t$ Effective Resistance

Speaker: Hong Zhou
Affiliation: University of Waterloo
Room: MC 5417

Abstract:

We consider a problem of designing a network with small $s$-$t$ effective resistance. In the problem, we are given an undirected graph $G=(V,E)$, two designated vertices $s,t \in V$, and a budget $k$.

Thursday, February 6, 2020 4:00 pm - 4:00 pm EST (GMT -05:00)

Graphs and Matroids Seminar - Richard Lang

Title: Minimum degree conditions for Hamilton cycles in hypergrahs

Speaker: Richard Lang
Affiliation: University of Waterloo
Room: MC 5479

Abstract:

A classic result of Dirac states that a graph in which every vertex is connected to at least half of the other vertices contains a Hamilton cycle. How can we generalize Dirac's theorem to hypergraphs?

Thursday, February 13, 2020 2:30 pm - 2:30 pm EST (GMT -05:00)

Algebraic Combinatorics Seminar - Brian Chan

Title: A generalization of balanced tableaux and matching problems with unique solutions

Speaker: Brian Chan
Affiliation: University of British Columbia
Room: MC 5417

Abstract:

In this talk, we consider families of finite sets that we call shellable and that have been characterized by Chang and Hirst and Hughes as being the families of sets that admit unique solutions to Hall's matching problem.

Thursday, February 13, 2020 4:00 pm - 4:00 pm EST (GMT -05:00)

Graphs and Matroids Seminar - Matt Kroeker

Title: List Colouring and Ohba's Conjecture

Speaker: Matt Kroeker
Affiliation: University of Waterloo
Room: MC 5479

Abstract:

The question of when the list-chromatic number of a graph G, denoted chi_l(G), equals its chromatic number is fundamental to the theory of list colouring.

Friday, February 14, 2020 1:00 pm - 1:00 pm EST (GMT -05:00)

Combinatorial Optimization Reading Group - Kanstantsin Pashkovich

Title: The Aggregation Closure is Polyhedral for Packing and Covering Integer Programs

Speaker: Kanstantsin Pashkovich
Affiliation: University of Ottawa
Room: MC 5417

Abstract:

Recently, Bodur, Del Pia, Dey, Molinaro and Pokutta introduced the concept of aggregation cuts for packing and covering integer programs.

Thursday, February 20, 2020 1:00 pm - 1:00 pm EST (GMT -05:00)

Algebraic Graph Theory Seminar - Chris Godsil

Title: Triangle-free Strongly Regular Graphs

Speaker: Chris Godsil
Affiliation: University of Waterloo
Room: MC 5417

Abstract:

Complete bipartite graphs aside, only five triangle-free strongly regular graphs are known. I will describe some of the background to this topic, with the focus on outlining the construction of the Higman-Sims graph.

Thursday, February 27, 2020 2:30 pm - 2:30 pm EST (GMT -05:00)

Algebraic Combinatorics Seminar - Ed Richmond

Title: An equivariant basis for the cohomology of Springer fibers

Speaker: Ed Richmond
Affiliation: Oklahoma State University
Room: MC 5417

Abstract:

Springer fibers are subvarieties of the flag variety that play an important role in combinatorics and geometric representation theory. In this talk, I will discuss joint work with Martha Precup where we analyze the equivariant cohomology of Springer fibers in type A.

Thursday, February 27, 2020 4:00 pm - 4:00 pm EST (GMT -05:00)

Graphs and Matroids Seminar - Farbod Yadegarian

Title: Excluding an asymmetric group labelled graph

Speaker: Farbod Yadegarian
Affiliation: University of Waterloo
Room: MC 5479

Abstract:

There are several models of group labelled graphs. In the simpler, undirected model, for an abelian group Γ, every edge e receives a label γ(e) in Γ.