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Wednesday, December 12, 2018 — 4:00 PM EST

Title: How to Escape Saddle Points Efficiently

Speaker: Matthew Slavin
Affiliation: University of Waterloo
Room: MC 5479

Abstract: We will discuss the 2017 paper named in the title of the talk, by Jin et al.

Wednesday, December 5, 2018 — 4:00 PM EST

Title: Stochastic subgradient method converges on tame functions

Speaker: Shenghao Yang
Affiliation: University of Waterloo
Room: MC 5479

Abstract: In this talk, I will present a paper (https://arxiv.org/abs/1804.07795) on the convergence of stochastic subgradient method in a nonconvex and nonsmooth setting.

Friday, November 30, 2018 — 3:30 PM EST

Title: Aggregation-based cutting-planes for packing and covering integer programs

Speaker: Merve Bodur
Affiliation: University of Toronto
Room: MC 5501

Abstract:

We study the strength of Chvatal-Gomory (CG) cuts and more generally aggregation cuts for packing and covering integer programs (IPs).

Friday, November 30, 2018 — 1:00 PM EST

Title: Clustering under Ordered Norms

Speaker: Sharat Ibrahimpur
Affiliation: University of Waterloo
Room: MC 5479

Abstract: In this talk we will see approximation algorithms for a broad class of objective functions called as ordered norms.

Thursday, November 29, 2018 — 3:30 PM EST

Title: Flag algebras and subgraph density problems

Speaker: Kris Siy
Affiliation: University of Waterloo
Room: MC 5417

Abstract: Flag algebras are a tool introduced by Razborov in 2007 that has since been successfully used to approach or solve many problems in asymptotic extremal combinatorics.

Wednesday, November 28, 2018 — 4:00 PM EST

Title: Convergence Rate of Block-Coordinate Maximization Burer-Monteiro Method for Solving Large SDP

Speaker: Sina Rezazadeh
Affiliation: University of Waterloo
Room: MC 5479

Abstract: Burer and Monteiro in 2003 proposed a nonlinear algorithm for solving semidefinite programs.

Tuesday, November 27, 2018 — 5:30 PM EST
Marc Morin

The "blood, sweat, tears, toil and triumphs" of commercializing technology

Friday, November 23, 2018 — 3:30 PM EST

Title: Implementing supersingular isogeny cryptography

Speaker: David Jao
Affiliation: University of Waterloo
Room: MC 5501

Abstract:

Recent years have seen dramatic progress and improvements in the implementation of supersingular isogeny-based cryptosystems.

Thursday, November 22, 2018 — 3:30 PM EST

Title: The upper density of monochromatic infinite paths

Speaker: Richard Lang
Affiliation: University of Waterloo
Room: MC 5417

Abstract: Given a complete graph $K_n$, whose edges are coloured in red and blue, what is the longest monochromatic path one can find?

Wednesday, November 21, 2018 — 4:00 PM EST

Title: Tutorial on Convolutional Neural Networks

Speaker: Haesol Im
Affiliation: University of Waterloo
Room: MC 5479

Abstract: We have seen stochastic gradient descent and automatic differentiation to help handle the big dimensionality of problems that often occur in machine learning.

Friday, November 16, 2018 — 3:30 PM EST

Title: Solving DNN Relaxations of the Quadratic Assignment Problem with ADMM and Facial Reduction

Speaker: Henry Wolkowicz
Affiliation: University of Waterloo
Room: MC 5501

Abstract:

The quadratic assignment problem, QAP, has many important applications ranging from the planning of building locations of a university, to the positioning of modules on a computer chip (VLSI design), to the design of keyboards.

Friday, November 16, 2018 — 1:00 PM EST

Title: Stability Yields a PTAS for k-Median and k-Means Clustering

Speaker: Adam Brown
Affiliation: University of Waterloo
Room: MC 5479

Abstract: Previously, we have seen a variety of approximation methods for k-median, and last week we saw

Thursday, November 15, 2018 — 3:30 PM EST

Title:  A Short Proof of the Containers Theorem for Hypergraphs

Speaker: Michelle Delcourt
Affiliation: University of Waterloo
Room: MC 6486

Abstract:  A modern trend in extremal combinatorics is extending classical results from the dense setting (e.g. Szemerédi's theorem)

Wednesday, November 14, 2018 — 4:00 PM EST

Title: Why Random Reshuffling Beats Stochastic Gradient Descent

Speaker: Julian Romero
Affiliation: University of Waterloo
Room: MC 5479

Abstract:  Over the first few lectures in the seminar we studied the Stochastic Gradient Descent (SGD) method

Friday, November 9, 2018 — 3:30 PM EST

Title: Approximation Algorithms for Distributionally Robust Stochastic Optimization

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

Abstract:

Two-stage stochastic optimization is a widely-used framework for modeling uncertainty, where we have a probability distribution over possible realizations of the data, called scenarios, and decisions are taken in two stages: we make first-stage decisions knowing only the underlying distribution and before a scenario is realized, and may take additional second-stage recourse actions after a scenario is realized.

Friday, November 9, 2018 — 1:00 PM EST

Title: Approximate Clustering without the Approximation

Speaker: Thomas Baxter
Affiliation: University of Waterloo
Room: MC 5417

Abstract: Previously in this CombOpt Reading Group series, we have discussed improving approximation factors for particular distance-based objective functions in clustering problems.

Thursday, November 8, 2018 — 3:30 PM EST

Title:  2-universality of random graphs.

Speaker: Gal Kronenberg
Affiliation: Tel Aviv University
Room:  *MC 6486* 

Abstract: For a family of graphs F, a graph G is F-universal if G contains every graph in F as a (not necessarily induced) subgraph.

Wednesday, November 7, 2018 — 4:00 PM EST

Title: Hamiltonian Descent Methods

Speaker: Guojun Zhang
Affiliation: University of Waterloo
Room: MC 5479

Abstract: In this talk, I will present a paper on the Hamiltonian descent methods

Friday, November 2, 2018 — 3:30 PM EDT

Title: Razborov's flag algebras: Ten years on

Speaker: Sergey Norin
Affiliation: McGill University
Room: MC 5501

Abstract:

Many of the classical results in extremal combinatorics were obtained by ingenious application of elementary techniques, such as induction and Cauchy-Schwarz inequality.

Friday, November 2, 2018 — 1:00 PM EDT

Title: Approximating k-Median via Pseudo-Approximation

Speaker: Sharat Ibrahimpur
Affiliation: University of Waterloo
Room: MC 5479

Abstract: In the last two talks we saw two approaches for approximating k-median.

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.

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