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

# Events - January 2020

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.

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