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November 2017

Wednesday, November 1, 2017 — 4:00 PM EDT

Title: A Stochastic Gradient Method with an Exponential Convergence Rate for Finite Training Sets

Speaker: Ryan Kinnear Affiliation: University of Waterloo Room: MC 5479

Abstract:

We will be discussing the paper (having the same title) by Roux, Schmidt, and Bach.  The authors propose a new stochastic gradient method for optimizing the sum of
 a finite set of smooth functions, where the sum is strongly convex.


Thursday, November 2, 2017 — 3:30 PM EDT

Title: A short proof of a forgotten result

Speaker: Bertrand Guenin Affiliation: University of Waterloo Room: MC 4042

Abstract:

Friday, November 3, 2017 — 3:30 PM EDT

Title: How we solve linear programs

Speaker: Laurent Poirrier Affiliation: University of Waterloo Room: MC 5501

Abstract:

Linear programming is one of the most fundamental tools in optimization, and its theoretical complexity is well understood. In practice though, things are quite different: Which types of problems can we really solve? What sizes? With what algorithms?

Wednesday, November 8, 2017 — 4:00 PM EST

Title: A Fast Iterative Shrinkage-Thresholding Algorithm for Linear Inverse Problems 

Speaker: Nargiz Kalantarova Affiliation: University of Waterloo Room: MC 5479

Abstract:

We will be discussing the paper (having the same title) by Amir Beck and Marc Teboulle. We consider the class of iterative shrinkage-thresholding algorithms (ISTA) for solving linear inverse problems arising in signal/image processing. This class of methods, which can be viewed as an extension of the classical gradient algorithm, is attractive due to its simplicity and thus is adequate for solving large-scale problems even with dense matrix data.

Thursday, November 9, 2017 — 3:30 PM EST

Title: An Introduction to Discrete Quantum Walks

Speaker: Harmony Zhan Affiliation: University of waterloo Room: MC 6486

Abstract:

We will introduce the concept of a discrete quantum walk, prove some of its properties, discuss its relation to different graph structures, and construct interesting walks from these structures such as self-dual embeddings.

Thursday, November 9, 2017 — 3:30 PM EST

Title: An application of graph "recolouring”

Speaker: Ben Moore Affiliation: University of Waterloo Room: MC 5479

Abstract:

I will prove that for any graph G, if there is an edge e such that G-e has less than (k-1)!/2 cycles of length zero mod k, then the chromatic number of G is less or equal to k.

Friday, November 10, 2017 — 3:30 PM EST

Title: Coloring (cap even hole)-free graphs

Speaker: Shenwei Huang Affiliation: Wilfrid Laurier University Room: MC 5501

Abstract:

An even cycle of length 4 or more is called an even hole. A cap is a cycle of length at least 5 with exactly one chord and that chord creates a triangle with the cycle. In this talk we consider (cap, even hole)-free graphs, i.e., graphs that do not contain any even hole or cap as an induced subgraph.

Wednesday, November 15, 2017 — 4:00 PM EST

Title: Proximal alternating linearized minimization for nonconvex and nonsmooth problems

Speaker: Stefan Sremac Affiliation: University of Waterloo Room: MC 5479

Abstract:

We will be discussing the paper (having the same title) by Jerome Bolte, Shoham Sabach and Marc Teboulle.  We introduce a proximal alternating linearized minimization (PALM) algorithm for solving a broad class of nonconvex and nonsmooth minimization problems.

Thursday, November 16, 2017 — 3:30 PM EST

Title: Constructing cospectral graphs with a different switching

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

Abstract:

Many years ago, Brendan McKay and I introduced a construction of pairs of cospectral graphs, sometimes known as local switching. In the same paper we introduced a second switching technique which produces, as special cases, the smallest pair of cospectral graphs and the smallest pair of connected cospectral graphs.

Thursday, November 16, 2017 — 3:30 PM EST

Title: Convex drawings of complete graphs:  topology meets geometry

Speaker: Bruce Richter Affiliation: University of Waterloo Room: MC 5479

Abstract:

A drawing D of the complete graph K(n) is the sphere is characterized by, for each isomorph J of K(5), D[J] is homeomorphic to one of the three rectilinear drawings of K(5).  Every drawing of K(n) in the plane with all edges straight-line segments is obviously convex.  Thus, convex drawings generalize planar point sets that are in general position. 

Friday, November 17, 2017 — 3:30 PM EST

Title: Recent Advances in Frank-Wolfe Optimization

Speaker: Simon Lacoste-Julien Affiliation: University of Montreal Room: MC 5501

Abstract:

The Frank-Wolfe (FW) optimization algorithm has lately re-gained popularity thanks in particular to its ability to nicely handle the structured constraints appearing in machine learning and signal processing applications. However, its convergence rate is known to be slow (sublinear) when the solution lies at the boundary.

Wednesday, November 22, 2017 — 4:00 PM EST

Title: Alternating Direction Method of Multipliers for the SDP Relaxation of the Quadratic Assignment Problem

Speaker: Henry Wolkowicz Affiliation: University of waterloo Room: MC 5479

Abstract:

The semidefinite programming (SDP) relaxation has proven to be extremely strong for many hard discrete optimization problems. This is in particular true for the quadratic assignment problem (QAP), arguably one of the hardest NP-hard discrete optimization problems.

Wednesday, November 22, 2017 — 4:30 PM EST

Title: Sum-of-Squares Proofs in Optimization

Speaker: Mehdi Karimi Affiliation: University of Waterloo Room: MC 5501

Abstract:

The old concept of sum-of-squares found its way into optimization and even machine learning. I will talk about this quickly evolving research area known as convex algebraic geometry.

Thursday, November 23, 2017 — 1:30 PM EST

Title: Orientations, Pseudoforests, Flows, and the Densest Subgraph
 

Speaker: Markus Blumenstock Affiliation: University of Mainz, Germany Room: MC 6486

Abstract:

Given an undirected graph, consider the problem of finding an orientation such that the max-imum indegree is minimized. The Gabow-Westermann algorithm can solve it by exploiting the matroid structure of pseudoforests.

Thursday, November 23, 2017 — 3:30 PM EST

Title: Ramsey theory for biased graphs

Speaker: Peter Nelson Affiliation:  University of Waterloo Room: MC 5479

Abstract:

We discuss the unavoidable subgraphs of biased graphs whose underlying graph is a clique.

Friday, November 24, 2017 — 3:30 PM EST

Title: Nash-Williams

Speaker: Joseph Cheriyan Affiliation: University of Waterloo Room: MC 5501

Abstract:

Crispin Nash-Williams was one of the founding professors of C&O. The talk will cover a small sample of his mathematical work, and also his association with C&O.

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