# Events - 2019

Friday, September 27, 2019 — 3:30 PM EDT

## Tutte Distinguished Lecture - Carsten Thomassen

Title: Countable weighted graphs with no unfriendly partitions

Wednesday, September 25, 2019 — 2:00 PM EDT

## Cryptography Reading Group - Jason LeGrow

Title: Improving Implementations of CSIDH

 Speaker: Jason LeGrow Affiliation: University of Waterloo Room: MC 5417

Abstract:

I will present on some papers related to implementations of CSIDH [1].

Friday, September 20, 2019 — 3:30 PM EDT

## Tutte Colloquium - Douglas Stebila

Title: Undermining key exchange

 Speaker: Douglas Stebila Affiliation: University of Waterloo Room: MC 5501

Abstract:

There are many ways to undermine systems that rely on cryptography. An attacker could of course try to find flaws in the hardware and software implementing the system, or find mathematical weaknesses in the cryptographic algorithms.

Friday, September 20, 2019 — 1:00 PM EDT

## Combinatorial Optimization Reading Group - Chaitanya Swamy

Title: Submodular function maximization

 Speaker: Chaitanya Swamy Affiliation: University of Waterloo Room: MC 5417

Abstract:

I will give the introductory talk for this term's topic for the Combinatorial-Optimization Reading group, namely submodular function maximization. Submodular functions arise in diverse contexts in combinatorial optimization.

Thursday, September 19, 2019 — 4:00 PM EDT

## Graphs and Matroids Seminar - Peter Nelson

Title: The sparsest matroids omitting an independent flat

 Speaker: Peter Nelson Affiliation: University of Waterloo Room: MC 5501

Abstract:

Given integers $k,r \ge 1$, what is the smallest a rank-$r$ matroid can be that does not contain a $k$-element independent set that is also a flat? I will answer this question, characterize the extremal examples, and draw parallels with a problem in graph theory.

Thursday, September 19, 2019 — 3:30 PM EDT

## Algebraic Combinatorics Seminar - Nick Olson-Harris

Title: When are two Schur functions the same?

 Speaker: Nick Olson-Harris Affiliation: University of Waterloo Room: MC 5417

Abstract:

A pair of skew shapes are said to be (skew) equivalent if they admit the same number of semistandard tableaux of any weight; i.e. if their associated skew Schur functions are equal.

Thursday, September 19, 2019 — 1:00 PM EDT

## Algebraic Graph Theory Seminar - Chris Godsil

TitleOrthogonal Polynomials and the Addition Formula

 Speaker: Chris Godsil Affiliation: University of Waterloo Room: MC 5479

Abstract:

Many questions about designs and codes in the unit sphere can be reduced to questions about members of a family of orthogonal polynomials, the so-called Gegenbauer polynomials.

Friday, September 13, 2019 — 3:30 PM EDT

## Tutte Colloquium - Richard Lang

Title: Monochromatic cycle partitions

 Speaker: Richard Lang Affiliation: University of Waterloo Room: MC 5501

Abstract:

A classic result of Erdős, Gyárfás, and Pyber states that the vertex set of every complete graph, whose edges have been coloured with r colours, can be covered by r2 log r disjoint monochromatic cycles.

Thursday, September 12, 2019 — 3:30 PM EDT

## Algebraic Combinatorics Seminar - Matthew Satriano

Title: Combinatorial questions motivated by Invariant Theory

 Speaker: Matthew Satriano Affiliation: University of Waterloo Room: MC 5417

Abstract:

We begin the talk by discussing a question in Invariant Theory: given a representation $V$ of a Lie group $G$, when if the invariant ring $k[V]^G$ a polynomial ring? We give a conjectural answer which we have verified for $SL_n$ and discuss some combinatorial questions motivated by the proof. This is joint work with Dan Edidin.

Thursday, September 12, 2019 — 1:00 PM EDT

## Algebraic Graph Theory Seminar - Chris Godsil

Title: Polynomial Spaces

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

Abstract:

We describe some simple machinery that enables us to derive upper bounds on the size of codes, and lower bounds on the size of designs in a quite general setting.

Friday, September 6, 2019 — 3:30 PM EDT

## Tutte Colloquium Seminar - Chaitanya Swamy

Title: Approximation Algorithms for Minimum-Norm Optimization Problems

 Speaker: Chaitanya Swamy Affiliation: University of Waterloo Room: MC 5501

Abstract:

In many optimization problems, a feasible solution induces a multidimensional cost vector. For example, in k-clustering, opening k facilities induces an assignment-cost vector indexed by the clients; in load-balancing, a schedule induces a load vector across the machines.

Thursday, September 5, 2019 — 1:00 PM EDT

## Algebraic Graph Theory Seminar - Maxwell Levit

Title: Signings and induced subgraphs of the Hypercube

 Speaker: Maxwell Levit Affiliation: University of Waterloo Room: MC 5479

Abstract:

Just over a month ago, Hao Haung resolved the sensitivity conjecture, a 30 year-old question about the complexity of boolean functions.

Tuesday, September 3, 2019 — 3:30 PM EDT

## Algebraic Combinatorics Seminar - Jason Brown

Title: Independence Polynomials and Their Roots

 Speaker: Jason Brown Affiliation: Dalhousie University Room: MC 5417

Abstract:

Independence polynomials are generating functions for the number of independent sets of each cardinality in a graph G.

Thursday, August 15, 2019 — 2:30 PM EDT

## Algebraic Graph Theory Seminar - Chris Godsil

Title: Upsetting Matrices

 Speaker: Chris Godsil Affiliation: University of Waterloo Room: MC 5479

Abstract:

If $A$ and $P$ are $n\times n$ matrices and the entries of $B$ are small, we may view $A+B$ as a perturbation of $A$, and expect that the spectral properties of $A+B$ should be related to those of $A$.
Thursday, August 8, 2019 — 2:30 PM EDT

## Algebraic Graph Theory - Soffia Arnadottir

Title: Continuous Quantum Walks

 Speaker: Soffia Arnadottir Affiliation: University of Waterloo Room: MC 5479

Abstract:

Continuous quantum walks are of considerable interest in quantum physics and quantum computing.

Tuesday, August 6, 2019 — 3:30 PM EDT

## Algebraic Combinatorics Seminar - Adrian Tanasa

Title: Feynman graphs, ribbon graphs and tensor graphs

 Speaker: Adrian Tanasa Affiliation: Université de Bordeaux Room: MC 5479

Abstract:

In this talk I will define the so-called Feynman graphs, which are a particular class of graphs appearing in quantum field theory.

Friday, August 2, 2019 — 3:30 PM EDT

## Tutte Colloquium - Jamie Sikora

Title: Optimization and Cryptography in Generalized Physical Theories

 Speaker: Jamie Sikora Affiliation: Perimeter Institute Room: MC 5501

Abstract:

In this talk, I will discuss three important cryptographic tasks in the quantum and post-quantum world. I will discuss the impossibility of bit-commitment and coin-flipping, and also the possibility of physically unforgeable money in the framework of Generalized Physical Theories (GPTs).

Friday, August 2, 2019 — 1:00 PM EDT

## Combinatorial Optimization Reading Group - Matthew Louis Gerstbrein

Title: Stable marraige with general preferences

 Speaker: Matthew Louis Gerstbrein Affiliation: University of Waterloo Room: MC 5479

Abstract:

This week, we discuss a generalization of the standard stable marriage problem, in which one side has a complete, totally ordered, strict preference list while the other has preferences given in terms of arbitrary binary relations.

Thursday, August 1, 2019 — 3:30 PM EDT

## Algebraic Combinatorics Seminar - Clair Dai

Title: Counting subdivergence-free gluing of trees

 Speaker: Clair Dai Affiliation: University of Waterloo Room: MC 5417

Abstract:

If we take two rooted trees with the same number of leaves and form a graph by gluing the leaves of one tree to the other, then we say the graph is subdivergence-free if no 2-edge cut have been generated.

Thursday, August 1, 2019 — 3:30 PM EDT

## Algebraic Combinatorics Seminar - Lily Wang

Title: The combinatorics of nearest and furthest values

 Speaker: Lily Wang Affiliation: University of Waterloo Room: MC 5417

Abstract:

A classical problem asks us to find, for each element $A[i]$ of an array of integers, the position of the nearest smallest element.

Thursday, August 1, 2019 — 3:30 PM EDT

## Algebraic Combinatorics Seminar - Yuval Ohapkin

Title: Bijections among symmetric tableaux via folding and mixed insertion

 Speaker: Yuval Ohapkin Affiliation: University of Waterloo Room: MC 5417

Abstract:

A standard Young tableau with entries $-M < \cdots -1 < 1 < \cdots < M$ can be "folded" by performing certain conversions and rectifications in sequence.

Thursday, August 1, 2019 — 2:30 PM EDT

## Algebraic Graph Theory - Chris Godsil

Title: Non-Commutative Algebras and Graphs

 Speaker: Chris Godsil Affiliation: University of Waterloo Room: MC 5479

Abstract:

I will discuss some of the non-commutative algebras that arise naturally in graph theory.

Friday, July 26, 2019 — 1:00 PM EDT

## Combinatorial Optimization Reading Group - Justin Toth

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

## Algebraic Combinatorics Seminar - Melanie Dennis

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

## Algebraic Graph Theory Seminar - Steve Kirkland

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.

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