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Monday, July 12, 2021 11:30 am - 11:30 am EDT (GMT -04:00)

Algebraic Graph Theory Seminar - Gabor Lippner

Title: Asymptotic quantum state transfer using two loops with large weights

Speaker: Gabor Lippner
Affiliation: Northeastern University
Zoom: Contact Soffia Arnadottir

Abstract:

We study the question of asymptotic transfer strength between two nodes of a graph when large weight loop edges are located at these nodes.  It turns out that the limiting strength can be exactly computed and depends only on the extended neighborhoods of the nodes.

Monday, July 19, 2021 11:30 am - 11:30 am EDT (GMT -04:00)

Algebraic Graph Theory Seminar - Michael Tait

Title: Two conjectures on the spread of graphs

Speaker: Michael Tait
Affiliation: Villanova University
Zoom: Contact Soffia Arnadottir

Abstract:

Given a graph $G$ let $\lambda_1$ and $\lambda_n$ be the maximum and minimum eigenvalues of its adjacency matrix and define the spread of $G$ to be $\lambda_1 - \lambda_n$. In this talk we discuss solutions to a pair of 20 year old conjectures of Gregory, Hershkowitz, and Kirkland regarding the spread of graphs.

Thursday, July 22, 2021 1:00 pm - 1:00 pm EDT (GMT -04:00)

Algebraic Combinatorics Seminar - Nadia Lafrenière

Title: The spectrum of the random-to-below Markov chain

Speaker: Nadia Lafrenière
Affiliation: Dartmouth College
Zoom: Contact Stephen Melczer

Abstract:

The random-to-below shuffle of a deck of cards consists of removing any card randomly (with uniform probability), and inserting it anywhere below (with uniform probability). When looking at the eigenvalues of its transition matrix, they all seem to be rational and positive.

Monday, July 26, 2021 11:30 am - 11:30 am EDT (GMT -04:00)

Algebraic Graph Theory Seminar - Thomas Wong

Title: Equivalent Laplacian and Adjacency Quantum Walks on Irregular Graphs

Speaker: Thomas Wong
Affiliation: Creighton University
Zoom: Contact Soffia Arnadottir

Abstract: 

The continuous-time quantum walk is a particle evolving by Schrödinger's equation in discrete space. Encoding the space as a graph of vertices and edges, the Hamiltonian is proportional to the discrete Laplacian. In some physical systems, however, the Hamiltonian is proportional to the adjacency matrix instead.

Wednesday, July 28, 2021 10:00 am - 10:00 am EDT (GMT -04:00)

Optimization: Theory, Algorithms, Applications Lecture Series

Title: A primal-dual interior-point algorithm fo rnonsymmetric conic optimization

Speaker: Erling D. Andersen
Affiliation: Mosek ApS
Zoom: Register through The Fields Institute

Abstract:

It is well known that primal-dual interior-point algorithms for linear optimization can easily be extended to the case of symmetric conic optimization, as shown by Nesterov and Todd (NT) in their 1997 paer about self-scaled barriers. Although many convex optimization problems can be expressed using symmetric cones then models involving for instance exponential functions do not belong to the class of symmetric conic optimization problems.

Friday, July 30, 2021 3:30 pm - 3:30 pm EDT (GMT -04:00)

Tutte Colloquium - Olya Mandelshtam

Title: Macdonald polynomials and the multispecies zero range process

Speaker: Olya Mandelshtam
Affiliation: University of Waterloo
Zoom: Please email Emma Watson

Abstract:

Over the last couple of decades, the theory of special functions and symmetric functions have found unexpected connections to various interacting particle systems. Macdonald polynomials are a family of symmetric functions that are known to have remarkable connections to a well-studied particle model called the ASEP. It is natural to ask whether the modified Macdonald polynomials can be obtained using a combinatorial gadget for some other particle system.

Monday, August 2, 2021 11:30 am - 11:30 am EDT (GMT -04:00)

Algebraic Graph Theory Seminar - Harmony Zhan

Title: The average search probability in a quantum walk with an oracle

Speaker: Harmony Zhan
Affiliation: York University
Zoom: Contact Soffia Arnadottir

Abstract:

Some quantum search algorithms can be viewed as discrete-time quantum walks on graphs with a marked vertex a. In such a walk, the oracle is part of the transition matrix, the target state is the characteristic vector of the outgoing arcs of a, and the initial state is the all-ones vector.

Friday, August 6, 2021 3:30 pm - 3:30 pm EDT (GMT -04:00)

Tutte Colloquium - Liana Yepremyan

Title: The size Ramsey numbers of graphs and hypergraphs

Speaker: Liana Yepremyan
Affiliation: London School of Economics
Zoom: Please email Emma Watson

Abstract:

The s-colour size-Ramsey number of a graph ( hypergraph) H is the minimum number of edges in a graph (hypergraph) G whose every s-edge-colouring contains a monochromatic copy of H. While the   study of size Ramsey numbers for graphs  goes back to 70's to the work of Erdos, Faudree, Rousseau and Schelp, the systematic study of these numbers for hypergraphs have been initiated much more recently in 2017  by Dudek, La Fleur, Mubayi, and Rödl. In this talk we will present the current known results in the literature, and some recent progress we have made on several questions in the area.

Wednesday, August 11, 2021 10:00 am - 10:00 am EDT (GMT -04:00)

Optimization: Theory, Algorithms, Applications Lecture Series

Title: TBA

Speaker: Jacek Gondzio
Affiliation: University of Edinburgh
Zoom: Register through The Fields Institute

Abstract: 

Having briefly introduced the key ideas which make interior point methods (IPMs) such a powerful optimization approach, I shall focus on a solution of the Newton systems and in particular on the use of iterative (Krylov-subspace) techniques to perform this task.

The Newton systems arising in IPMs are inherently ill-conditioned and preconditioning is a must to make iterative methods work.

A re-design of IPMs to enable the use of iterative techniques provides a completely new perspective on these methods.

I will address both theoretical and practical aspects of it.