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Wednesday, December 13, 2017 — 4:00 PM EST

Title: Generalized Conditional Gradient for Sparse Estimation

Speaker: Yaoliang Yu  
Affiliation: University of Waterloo
Room: MC 5479

Abstract:

We will be discussing the paper (bearing the same title) of Yaoliang Yu, Xinhua Zhang, and Dale Schuurmans.  Structured sparsity is an important modelling tool that expands the applicability of convex formulations for data analysis, however it also creates significant challenges for efficient algorithm design.

Thursday, December 7, 2017 — 3:30 PM EST

Title: Continuous Quantum Walks and Symmetric Powers

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

Abstract:

The k-th symmetric power of a graph X has the k-subsets of V(X) as its vertices, and two k-subsets are adjacent if their symmetric difference is an edge in X. A continuous quantum walk on a graph gives rise in a natural walk to walks on it symmetric powers.

Wednesday, December 6, 2017 — 4:00 PM EST

Title: Signal Recovery by Proximal Forward-Backward Splitting

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

Abstract:

We will be discussing the paper (bearing the same title) of Patrick Combettes and Valérie Wajs.  We show that various inverse problems in signal recovery can be formulated as the generic problem of minimizing the sum of two convex functions with certain regularity properties.

Friday, December 1, 2017 — 3:30 PM EST

Title: Turan problems for matroids

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

Abstract:

Given a fixed simple binary matroid N, what is the maximum size of a simple rank-r binary matroid that does not contain N a restriction?

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

Title: Asymmetric Latin squares, Steiner triple systems, and 1-factorizations

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

Abstract:

We outline how the Van der Waerden permanent theorem can be used to show that almost all Latin squares, Steiner triple systems, and 1-factorizations of the complete graph admit only trivial automorphisms. 

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

Title: Fragility and circuit-hyperplane relaxation

Speaker: Jim Geelen
Affiliation: University of Waterloo
Room : MC 5479

Abstract:

I will briefly discuss the problem of trying to determine the excluded minors for the class of GF(5)-representable matroids, highlighting the roles of N-fragility and of circuit-hyperplane relaxations.

Wednesday, November 29, 2017 — 4:00 PM EST

Title: Efficient First-Order Methods for Linear Programming and Semidefinite Programming 

Speaker: Leanne Stuive
Affiliation: University of Waterloo
Room: MC 5479

Abstract:

We will be discussing the paper (bearing the same title) of James Reneger.  We present a simple transformation of any linear program or semidefinite program into an equivalent convex optimization problem whose only constraints are linear equations. The objective function is defined on the whole space, making virtually all subgradient methods be immediately applicable.

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.

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.

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.

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.

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.

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.

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. 

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.

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.

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:

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.

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.

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?

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:

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.


Friday, October 27, 2017 — 3:30 PM EDT

Title: Some matrix problems in quantum information science

Speaker: Chi-Kwong Li
Affiliation: College of William and Mary, IQC
Room: MC 5501

Abstract:

In this talk, we present  some matrix results and techniques in solving certain optimization problems arising  in quantum information science.

No quantum mechanics background is required.

Thursday, October 26, 2017 — 3:30 PM EDT

Title: Progress on Continuous Quantum Walks

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

Abstract:

I will discuss the progress we’ve made in our work on continuous walks. I will start with old stuff (last November) and continue on to current stuff (this week).

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