Events - October 2018

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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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