## 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 - October 2018

Friday, October 26, 2018 — 3:30 PM EDT

## Tutte Colloquium - Jim Geelen

Title: Vertex Minors

 Speaker: Jim Geelen Affiliation: University of Waterloo Room: MC 5501

Abstract:

I will give an introduction to vertex-minors of graphs. At first sight vertex minors are a bit peculiar but they are closely related to graph minors and possibly even easier to work with.

Friday, October 26, 2018 — 1:00 PM EDT

## CombOpt Reading Group- Zishen Qu

Title:Local Search Guarantees on Facility Location Problems

 Speaker: Zishen Qu Affiliation: University of Waterloo Room: MC 5479

Abstract: We will show that guarantees can be given on algorithms for the k-median problem based on local search heuristics.

Thursday, October 25, 2018 — 3:30 PM EDT

## Graphs and Matroids Seminar- Gholam Reza Omidi

Title: Some problems on the size Ramsey numbers

 Speaker: Gholam Reza Omidi Affiliation: Isfahan University of Technology Room: MC 5417

Abstract: For given simple graphs $G_1$ and $G_2$, the size Ramsey number $\hat{R}(G_1,G_2)$ is the smallest positive integer $m$,

Thursday, October 25, 2018 — 1:30 PM EDT

## Algebraic Graph Theory Seminar- Nathan Lindzey

Title: Maximum Independent Sets in Erdos-Ko-Rado Combinatorics

 Speaker: Nathan Lindzey Affiliation: University of Waterloo Room: MC 6486

Abstract:  We discuss a general algebraic method for characterizing maximum independent sets in graphs that arise in Erdos-Ko-Rado combinatorics, provided the graphs are large enough.

Friday, October 19, 2018 — 3:30 PM EDT

## Tutte Colloquium - Matthias Mnich

Title: New algorithms for maximum disjoint paths based on tree-likeness

 Speaker: Matthias Mnich Affiliation: University of Bonn Room: MC 5501

Abstract:

We study the classical NP-hard problems of finding maximum-size subsets from given sets of k terminal pairs that can be routed via edge-disjoint paths (MaxEDP) or node-disjoint paths (MaxNDP) in a given graph.

Friday, October 19, 2018 — 1:00 PM EDT

## Combinatorial Optimization

Title: Primal-dual and Lagrangian relaxation techniques for k-median

 Speaker: Madison Van Dyk Affiliation: University of Waterloo Room: MC 5479

Abstract: We will develop primal-dual algorithms to obtain constant-factor approximations for the uncapacitated facility location problem.

Thursday, October 18, 2018 — 3:30 PM EDT

## Graphs and Matroids Seminar

Title: Extending Thomassen’s Theorem to Two Faces

 Speaker: Joshua Nevin Affiliation: University of Waterloo Room: MC 5417

Abstract:

Let G be a planar graph and let L be a list-assignment for G in which there is a precolored edge on the outer face, every other vertex on the outer face has a list of size at least 3, and every other vertex in G has a list of size at least 5.

Thursday, October 18, 2018 — 1:30 PM EDT

## Algebraic Graph Theory Seminar- Chris Godsil

Title: Graphs of Homomorphisms

 Speaker: Chris Godsil Affiliation: University of Waterloo Room: MC 6486

Abstract: If X and Y are graphs and f is a function on V (X) taking values in V (Y ), then the graph of
f is the subset formed by the pairs (x; f(x)) for x in V (X).

Wednesday, October 17, 2018 — 4:00 PM EDT

## Continuous Optimization Seminar - Steve Vavasis

Title: Tutorial on back-propagation and automatic differentiation

 Speaker: Steve Vavasis Affiliation: University of Waterloo Room: MC 5479

Abstract: In this presentation, I'll cover the basics of automatic differentiation (AD).

Wednesday, October 17, 2018 — 3:30 PM EDT

## Combinatorics and Optimization Graduate Student Colloquium

Title: Basis Shape Loci and the Positive Grassmannian

 Speaker: Cameron Marcot Affiliation: University of Waterloo Room: MC 6483

Abstract: We study the set of k-dimensional planes in R^n admitting a basis of vectors with prescribed supports.

Friday, October 12, 2018 — 10:30 AM EDT

## Special Seminar - Gareth Davies

Title: Offline Assisted Group Key Exchange

 Speaker: Gareth Davies Affiliation: Norwegian University of Science and Technology (NTNU) Room: MC 5417

Abstract:

This talk will focus on the problem of forward secrecy in group key exchange (GKE), where most of the participants remain offline until they wish to compute the key.

Thursday, October 4, 2018 — 3:30 PM EDT

## Graphs and Matroids Seminar

Title: Representable orientable matroids that are not real-representable

 Speaker: Rutger Campbell Affiliation: University of Waterllo Room: MC 5417

Abstract: In this talk we will have a brief introduction to oriented matroids and their relation to real-representability.

Thursday, October 4, 2018 — 1:30 PM EDT

## Algebraic Graph Theory Seminar

Title: Controllable graphs

 Speaker: Chris Godsil Affiliation: University of Waterloo Room: MC 6486

Abstract: A graph is controllable if no eigenvector is orthogonal to the all-ones vector.

Wednesday, October 3, 2018 — 4:00 PM EDT

## Continuous Optimization Seminar

Title: Review of martingale theory, stochastic gradient descent, and adaptive line-line-search for stochastic optimization.

 Speaker: Courtney Paquette Affiliation: University of Waterloo Room: MC 5479

Abstract: With the rise of large data sets, practical algorithms for machine learning often use probability and statistics.

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