Events

Filter by:

Limit to events where the first date of the event:
Date range
Limit to events where the first date of the event:
Limit to events where the title matches:
Limit to events where the type is one or more of:
Limit to events tagged with one or more of:
Limit to events where the audience is one or more of:
Friday, May 28, 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
Affliliation: University of Waterloo
Zoom: Contact Emma Watson

Abstract:

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. 

Monday, May 31, 2021 11:30 am - 11:30 am EDT (GMT -04:00)

Algebraic Graph Theory Seminar - Jo Ellis-Monaghan

Title: An algebraic framework for twualities of embedded graphs

Speaker: Jo Ellis-Monaghan
Affiliation: Korteweg-de Vries Instituut voor Wiskunde, Universiteit van Amsterdam
Zoom: Contact Soffia Arnadottir

Abstract:

We develop algebraic tools to identify and generate new surface embeddings of graphs with various forms of self-twuality including geometric duality, Petrie duality, Wilson duality, and both forms of triality (which is like duality, but of order three instead of two).  These operations are of particular interest because of their interplay with graph symmetries and graph polynomials.

Thursday, June 3, 2021 1:00 pm - 1:00 pm EDT (GMT -04:00)

Algebraic Combinatorics Seminar - Oliver Pechenik

Title: What is the degree of a Grothendieck polynomial?

Speaker: Oliver Pechenik
Affiliation: University of Waterloo
Zoom: Contact Stephen Melczer

Abstract:

Jenna Rajchgot observed that the Castelnuovo-Mumford regularity of matrix Schubert varieties is computed by the degrees of the corresponding Grothendieck polynomials. We give a formula for these degrees.

Friday, June 4, 2021 3:30 pm - 3:30 pm EDT (GMT -04:00)

Tutte Colloquium - Kanstantsin Pashkovich

Title: On the approximability of the maximum cardinality stable matching problem with ties  

Speaker: Kanstantsin Pashkovich
Affliliation: University of Waterloo
Zoom: Contact Emma Watson

Abstract:

The maximum cardinality stable matching problem is central in game theory. When participants are allowed to have ties in their preferences, the problem of finding a stable matching of maximum cardinality is NP-hard, even when the ties are of size two. Moreover, in this setting it is UGC-hard to provide an approximation for the maximum cardinality stable matching problem with a constant factor smaller than 4/3.

Thursday, June 10, 2021 1:00 pm - 1:00 pm EDT (GMT -04:00)

Algebraic Combinatorics Seminar - Lukas Nabergall

Title: Enumerating hereditary classes of chord diagrams

Speaker: Lukas Nabergall
Affiliation: University of Waterloo
Zoom: Contact Stephen Melczer

Abstract:

A class of combinatorial structures is hereditary if membership in the class is closed under taking substructures. Hereditary classes have been extensively studied for a variety of objects, notably graphs and permutations. A central problem is to determine the number of objects of size n in a given hereditary class. We discuss this problem for chord diagrams, perfect matchings of [2n].

Thursday, June 10, 2021 4:00 pm - 4:00 pm EDT (GMT -04:00)

Joint Colloquium - Shayla Redlin

Title: Counting Antichains in the Boolean Lattice

Speaker: Shayla Redlin
Affiliation: University of Waterloo
Zoom: Contact Maxwell Levit

Abstract:

How many antichains are there in the Boolean lattice P(n)? Sperner's theorem (1928) tells us that the largest antichain in P(n) has size A = (n choose n/2). A subset of an antichain is an antichain, so there are at least 2^A antichains in P(n). Interestingly, it turns out that this is close to the total, as Kleitman (1969) showed that the number of antichains is 2^(A(1+x)) where x goes to zero as n goes to infinity.

Friday, June 11, 2021 3:30 pm - 3:30 pm EDT (GMT -04:00)

Tutte Colloquium - Cécile Pierrot

Title: The discrete logarithm problem in finite fields

Speaker: Cécile Pierrot
Affliliation: French National Institute for Computer Science Research (INRIA)
Zoom: Contact Emma Watson

Abstract:

The security of currently deployed public key protocols relies on the presumed hardness of problems often coming from number theory, such as factoring a large integer or solving the discrete logarithm problem in some group.

In this talk we focus on discrete logarithms in finite fields. We explain what is a discrete logarithm, why cryptographers need them, and we focus then on algorithms to solve the related problem, together with open questions in this area.

Thursday, June 17, 2021 1:00 pm - 1:00 pm EDT (GMT -04:00)

Algebraic Combinatorics Seminar - Angèle Hamel

Title: Identities for ninth variation Schur Q-functions

Speaker: Angèle Hamel
Affiliation: Wilfrid Laurier University
Zoom: Contact Stephen Melczer

Abstract:

Recently Okada defined algebraically ninth variation skew Q-functions, in parallel to Macdonald's ninth variation skew Schur functions. Here we introduce a skew shifted tableaux definition of these ninth variation skew Q-functions, and prove by means of a non-intersecting lattice path model a Pfaffian outside decomposition result in the form of a ninth variation version of Hamel's Pfaffian outside decomposition identity.

Friday, June 18, 2021 11:30 am - 11:30 am EDT (GMT -04:00)

Algebraic Graph Theory Seminar - Dheer Noal Desai

Title: The spectral radius of graphs with no odd wheels

Speaker: Dheer Noal Desai
Affiliation: University of Delaware
Zoom: Contact Soffia Arnadottir

Abstract:

The odd wheel W_{2k+1} is the graph formed by joining a vertex to a cycle of length 2k. In this talk, we will investigate the largest value of the spectral radius of the adjacency matrix of an n-vertex graph that does not contain W_{2k+1}.

Friday, June 18, 2021 3:30 pm - 3:30 pm EDT (GMT -04:00)

Tutte Colloquium - Marni Mishna

Title: Lattice Walk Enumeration: Analytic, algebraic and geometric aspects

Speaker: Marni Mishna 
Affliliation: Simon Fraser University
Zoom: Contact Emma Watson

Abstract:

This talk will examine the rich topic of lattice path enumeration. A very classic object of combinatorics, lattice walks withstand study from a variety of perspectives. Even the simple task of classifying the two dimensional walks restricted to the first quadrant has brought into play a surprising diversity of techniques from algebra to analysis to geometry. We will consider walks under a few different lenses.