## University COVID-19 update

### Questions about buildings and services? Visit the list of Modified Services.

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

# Events - 2020

Thursday, February 27, 2020 — 2:30 PM EST

## 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 — 1:00 PM EST

## Algebraic Graph Theory Seminar - Sabrina Lato

Title: Linear Programming and Extremal Expanders

 Speaker: Sabrina Lato Affiliation: University of Waterloo Room: MC 5417

Abstract:

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

Thursday, February 20, 2020 — 1:00 PM EST

## 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.

Friday, February 14, 2020 — 1:00 PM EST

## 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 13, 2020 — 4:00 PM EST

## 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.

Thursday, February 13, 2020 — 2:30 PM EST

## 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 — 1:00 PM EST

## Algebraic Graph Theory Seminar - Chris Godsil

Title: Moore Graphs

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

Abstract:

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

Thursday, February 6, 2020 — 4:00 PM EST

## 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?

Friday, January 31, 2020 — 1:00 PM EST

## 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, January 30, 2020 — 4:00 PM EST

## Graphs and Matroids Seminar - Paul Wollan

 Speaker: Paul Wollan Affiliation: Sapienza Università di Roma Room: MC 5479

Abstract:

A folklore result says that if a graph does not contain the path of length k as a subgraph, then it has tree-depth at most k.

Thursday, January 30, 2020 — 2:30 PM EST

## Algebraic Combinatorics Seminar - Neal Madras

Title: Random Pattern-Avoiding Permutations

 Speaker: Neal Madras Affiliation: York University Room: MC 5417

Abstract:

A "pattern of length k" is simply a permutation of {1,..,k}.  This pattern is said to be contained in a permutation of {1,...,N} (for N>k) if there is a subsequence of k elements of the (long) permutation that appears in the same relative order as the pattern.

Friday, January 24, 2020 — 1:00 PM EST

## Combinatorial Optimization Reading Group - Ben Moore

Title: On the Strong Nine Dragon Tree Conjecture

 Speaker: Ben Moore Affiliation: University of Waterloo Room: MC 5417

Abstract:

Nash-Williams forest covering theorem says that a graph decomposes into $k$ forests if and only if it has fractional arboricity at most $k$. In 2012 Mickeal Montassier, Patrice Ossona de Mendez, Andre Raspaud, and Xuding Zhu  proposed a significant strengthening of Nash-Williams Theorem, called the Strong Nine Dragon Tree Conjecture.

Thursday, January 23, 2020 — 4:00 PM EST

## Graphs and Matroids Seminar - Jane Gao

Title: Uniformly generate graphs with given degrees rapidly

 Speaker: Jane Gao Affiliation: University of Waterloo Room: MC 5479

Abstract:

I will survey the research on exact/approximate uniform generation of graphs with prescribed degrees.

Thursday, January 23, 2020 — 2:30 PM EST

## Algebraic Combinatorics Seminar - Karen Yeats

Title: Some places matroids appear in quantum field theory and some places I would like them to

 Speaker: Karen Yeats Affiliation: University of Waterloo Room: MC 5417

Abstract:

I will discuss some places matroids have appeared in my work in quantum field theory, including some older work on numerator structure with Dirk Kreimer and some work in progress with Iain Crump on period identities.

Friday, January 17, 2020 — 1:00 PM EST

## Combinatorial Optimization Reading Group - Ishan Bansal

Title: The Capacitated Survivable Network Design Problem

 Speaker: Ishan Bansal Affiliation: University of Waterloo Room: MC 5417

Abstract:

The Capacitated Survivable Network Design Problem or Cap-SNDP models a network reinforcement problem where the network designer wants to find a minimum-cost set of reinforcements that protects the network from an adversary.

Thursday, January 16, 2020 — 2:03 PM EST

## Algebraic Combinatorics Seminar - David Wagner

Title: Electrical networks, random spanning trees, and matroids

 Speaker: David Wagner Affiliation: University of Waterloo Room: MC 5417

Abstract:

This is a reprise of a survey talk I gave at the East Coast Combinatorics Conference in August 2019, and a variation of one I gave in the graphs and matroids seminar last year.

Thursday, January 16, 2020 — 1:00 PM EST

## Algebraic Graph Theory Seminar - Chris Godsil

Title: Covers of Complete Bipartite Graphs

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

Abstract:

I will discuss antipodal distance-regular covers of complete bipartite graphs $K_{n,n}$. The index of such a cover is at most $n$.

Friday, January 10, 2020 — 1:00 PM EST

## Combinatorial Optimization Reading Group - Logan Grout

Title: Beating 3/2 for Approximating TSP in the Half-Integral Case

 Speaker: Logan Grout Affiliation: University of Waterloo Room: MC 5417

Abstract:

In 2013, Schalekamp, Williamson, and van Zuylen conjectured that the integrality gap for the Subtour Polytope was attained on its half-integral vertices.

Thursday, January 9, 2020 — 1:00 PM EST

## Algebraic Graph Theory Seminar - Chris Godsil

Title: Periodicity in Quantum Walks

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

Abstract:

Despite the title, quantum walks are, in general, not periodic. However they are, in general, periodic to any desired degree of accuracy.

## Pages

### January 2021

S M T W T F S
27
28
29
30
31
1
2
3
5
6
7
8
9
10
12
13
16
17
19
20
23
24
26
27
30
31
1
2
3
4
5
6
1. 2021 (37)
1. April (6)
2. March (13)
3. February (8)
4. January (10)
2. 2020 (119)
1. December (5)
2. November (12)
3. October (12)
4. September (12)
5. August (11)
6. July (17)
7. June (11)
8. May (6)
9. March (11)
10. February (11)
11. January (11)
3. 2019 (167)
4. 2018 (136)
5. 2017 (103)
6. 2016 (137)
7. 2015 (136)
8. 2014 (88)
9. 2013 (48)
10. 2012 (39)
11. 2011 (36)
12. 2010 (40)
13. 2009 (40)
14. 2008 (39)
15. 2007 (15)