Events

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

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 $k$.

Title: Minimum degree conditions for Hamilton cycles in hypergrahs

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?

Title: Moore Graphs

Abstract:

Moore graphs were introduced by Hoffman and Singleton in a fundamental paper. They can be defined as graphs with diameter $d$ and girth $2d+1$.

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

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.

Title: List Colouring and Ohba's Conjecture

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.

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

Abstract:

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

Title: Triangle-free Strongly Regular Graphs

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.

Title: Linear Programming and Extremal Expanders

Abstract:

Nozaki proved a linear programming bound on the number of vertices that depends on the eigenvalues of a graph.

Title: An equivariant basis for the cohomology of Springer fibers

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.

Title: Excluding an asymmetric group labelled graph

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.