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Friday, June 26, 2020 3:30 pm - 3:30 pm EDT (GMT -04:00)

Tutte Colloquium - David Wagner

Title: Discrete diffusion on graphs and real hyperplane arrangements

Speaker: David Wagner
Affiliation: University of Waterloo
Zoom: Please email Emma Watson
To view the slides: Click here


In 2016, Duffy, Lidbetter, Messinger, and Nowakowski introduced the following variation of a chip-firing model on a graph. At time zero, there is an integer number of "chips" at each vertex. Time proceeds in discrete steps.  At each step, each edge is examined (in parallel) -- one chip is moved from the greater end to the lesser end if the ends are not equal.

Friday, September 4, 2020 3:30 pm - 3:30 pm EDT (GMT -04:00)

Tutte Colloquium - Joseph Paat

Title: Recent proximity results in integer linear programming

Speaker: Joseph Paat
Affiliation: UBC Sauder School of Business
Zoom: Please email Emma Watson.


We consider the proximity question in integer linear programming (ILP) --- Given a vector in a polyhedron, how close is the nearest integer vector? Proximity has been studied for decades with two influential results due to Cook et al. in 1986 and Eisenbrand and Weismantel in 2018. We derive new upper bounds on proximity using sparse integer solutions and mixed integer relaxations of the integer hull. When compared to previous bounds, these new bounds depend less on the dimensions of the constraint matrix and more on the data in the matrix.

Monday, November 2, 2020 11:30 am - 11:30 am EST (GMT -05:00)

Algebraic Graph Theory Seminar - Sabrina Lato & Christino Tamon

Title: Monogamy Violations in Perfect State Transfer

Speakers: Sabrina Lato & Christino Tamon
Affiliations: University of Waterloo & Clarkson Unversity
Zoom: Contact Soffia Arnadottir


Continuous-time quantum walks on a graph are defined using a Hermitian matrix associated to a graph. For a quantum walk on a graph using either the adjacency matrix or the Laplacian, there can be perfect state transfer from a vertex to at most one other vertex in the graph.

Friday, November 6, 2020 3:30 pm - 3:30 pm EST (GMT -05:00)

Tutte Colloquium - Chloe Martindale

Title: Constructing broken SIDH parameters: a tale of De Feo, Jao, and Plut's serendipity

Speaker: Chloe Martindale
Affiliation: University of Bristol
Zoom: Please email Emma Watson


This talk is motivated by analyzing the security of the cryptographic key exchange protocol SIDH (Supersingular Isogeny Diffie-Hellman), introduced by 2011 by De Feo, Jao, and Plut. We will first recall some mathematical background as well as the protocol itself. The 'keys' in this protocol are elliptic curves, which are typically described by equations in x and y of the form y^2 = x^3 + ax + b.

Friday, February 26, 2021 3:30 pm - 3:30 pm EST (GMT -05:00)

Tutte Colloquium - Robert Morris

Title: Flat Littlewood Polynomials Exist

Speaker: Robert Morris
Affliation: IMPA (Instituto de Matemática Pura e Aplicada)
Zoom: Please email Emma Watson


In a Littlewood polynomial, all coefficients are either 1 or -1. Littlewood proved many beautiful theorems about these polynomials over his long life, and in his 1968 monograph he stated several influential conjectures about them. One of the most famous of these was inspired by a question of Erdos, who asked in 1957 whether there exist "flat" Littlewood polynomials of degree n, that is, with |P(z)| of order n^{1/2} for all (complex) z with |z| = 1. 

Friday, March 12, 2021 3:30 pm - 3:30 pm EST (GMT -05:00)

Tutte Colloquium - Bill Cook

Title: An approximate solution to a 2,079,471-point traveling salesman problem

Speaker: Bill Cook
Affliation: University of Waterloo
Zoom: Please email Emma Watson


Together with Keld Helsguan, we have found a TSP tour through the 3D positions of 2,079,471 stars. We discuss how linear programming allows us to prove the tour is at most a factor of 0.0000074 longer than an optimal solution. The talk will focus on the use of minimum cuts and GF(2) linear systems, to drive the cutting-plane method towards strong LP relaxations.

Friday, April 9, 2021 3:30 pm - 3:30 pm EDT (GMT -04:00)

Tutte Colloquium - Alicia Kollár

Title: Circuit QED Lattices: Synthetic Quantum Systems on Line Graphs

Speaker: Alicia Kollár
Affliliation: University of Maryland
Zoom: Contact Emma Watson


After two decades of development, superconducting circuits have emerged as a rich platform for quantum computation and simulation. Lattices of coplanar waveguide (CPW) resonators realize artificial photonic materials or photon-mediated spin models. Here I will highlight the special property that these lattice sites are deformable and allow for the implementation of devices with graph-like configurational flexibility. In particular, I will show that it is possible to create synthetic materials in which microwave photons experience negative curvature, which is impossible in conventional electronic materials [1].

Monday, July 19, 2021 4:15 pm - 4:15 pm EDT (GMT -04:00)

Special SIAM Annual Meeting Session

Title: In Memoriam: Tom Coleman’s Contributions to Applied Mathematics and Optimization

Speaker: Yuying Li, Stephen Wright, Alex Pothen, Bruce Hendrickson, Peter Forsyth, and Somayeh Moazeni
Affiliation: SIAM Annual Meeting (AN21)


Friday, July 23, 2021 3:30 pm - 3:30 pm EDT (GMT -04:00)

Tutte Colloquium - Jon Yard

Title: Algebraic formulations of Zauner's conjecture

Speaker: Jon Yard
Affiliation: University of Waterloo
Zoom: Please email Emma Watson


Tight complex projective 2-designs are simultaneously maximal sets of equiangular lines and minimal complex projective 2-designs. In quantum information theory, they define optimal measurements known as SIC-POVMs (Symmetric Informationally Complete Positive Operator-Valued Measures).  They are conjectured by Zauner to exist in every dimension, even as specific group orbits.  Yet, they have only so far been proven to exist in a finite-but-growing list of dimensions via exact, explicit constructions over increasingly high-degree number fields, since identified as specific class fields of real quadratic number fields.

Title: Semidefinite Optimization Approaches for Reactive Optimal Power Flow Problems

Speaker: Miguel Anjos
Affiliation: University of Edinburgh
Zoom: Register through The Fields Institute


The Reactive Optimal Power Flow (ROPF) problem consists in computing an optimal power generation dispatch for an alternating current transmission network that respects power flow equations and operational constraints. Some means of voltage control are modelled in ROPF such as the possible activation of shunts, and these controls are modelled using discrete variables. The ROPF problem belongs to the class of nonconvex MINLPs, which are NP-hard problems. We consider semidefinite optimization approaches for solving ROPF problems and their integration into a branch-and-bound algorithm.