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Friday, November 5, 2021 3:30 pm - 3:30 pm EDT (GMT -04:00)

Tutte Colloquium - László Végh

Title: On complete classes of valuated matroids

Speaker: László Végh
Affiliation: London School of Economics
Zoom: Please email Emma Watson

Abstract:

Valuated matroids were introduced by Dress and Wenzel in 1992. They are a central object in discrete convex analysis, and play important roles in other areas such as mathematical economics and tropical geometry. Finding a constructive characterization, i.e., showing that all valuated matroids can be derived from a simple class by some basic operations has been a natural question proposed in various contexts.

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

Tutte Colloquium - Greg Zaverucha

Title: Shorter Zero-Knowledge Proofs from MPC

Speaker: Greg Zaverucha
Affiliation: Microsoft Research
Zoom: Please email Emma Watson

Abstract:

In this talk I will review the MPC-in-the-head approach to constructing zero-knowledge proofs, then talk about some recent research results to make the proofs shorter.

In a zero-knowledge proof system, a prover wants to convince a verifier that they know a secret value, without revealing it. A common case involves a one-way function, where the prover wants to convince a verifier that they know a secret input corresponding to a public output.

Friday, November 19, 2021 3:30 pm - 3:30 pm EST (GMT -05:00)

Tutte Colloquium - Steph van Willigenburg

Title: The (3+1)-free conjecture of chromatic symmetric functions

Speaker: Steph van Willigenburg
Affiliation:

University of British Columbia

Zoom: Please email Emma Watson

Abstract:

The chromatic symmetric function, dating from 1995, is a generalization of the chromatic polynomial. A famed conjecture on it, called the Stanley-Stembridge (3+1)-free conjecture, has been the focus of much research lately. In this talk we will be introduced to the chromatic symmetric function, the (3+1)-free conjecture, new cases and tools for resolving it, and answer another question of Stanley of whether the (3+1)-free conjecture can be widened. This talk requires no prior knowledge.

Monday, November 22, 2021 11:30 am - 11:30 am EST (GMT -05:00)

Algebraic Graph Theory Seminar - Emily King

Title: Switching Equivalence on the Grassmannian

Speaker: Emily King
Affiliation: Colorado State University
Zoom: Contact Soffia Arnadottir

Abstract:

When constructing configurations of subspaces with desirable properties, one might ask if the configuration is indeed "new.''  It has been known for about 50 years that Gram matrices of equiangular vectors in real Euclidean space correspond to finite simple graphs via the Seidel adjacency matrix, and the collections of such vectors which span the same lines correspond to switching equivalence classes of graphs.

Monday, November 29, 2021 11:30 am - 11:30 am EST (GMT -05:00)

Algebraic Graph Theory Seminar - Peter Dukes

Title: Fractional decompositions and Latin square completion

Speaker: Peter Dukes
Affiliation: University of Victoria
Zoom: Contact Soffia Arnadottir

Abstract:

It was shown recently by Delcourt and Postle that any sufficiently large graph $G$ of order $n$ with minimum degree at least $0.827n$ has a fractional triangle decomposition, i.e. an assignment of weights to the triangles in $G$ such that for every edge $e$, the total of all weights of triangles containing $e$ is exactly one.

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

Tutte Colloquium - Minh Bui

Title: Warped Proximal Iterations for Multivariate Convex Minimization in Hilbert Spaces

Speaker: Minh Bui
Affiliation: University of Waterloo
Zoom: Please email Emma Watson

Abstract:

We propose a multivariate convex minimization model which involves a mix of nonsmooth and smooth functions, as well as linear mixtures of the variables. This formulation captures a wide range of concrete scenarios in the literature. A limitation of existing methods is that they do not achieve full splitting of our problem in the sense that each function and linear operator is activated separately. To circumvent this issue, we propose a novel approach, called warped proximal iterations, for solving this problem.

Monday, December 6, 2021 11:30 am - 11:30 am EST (GMT -05:00)

Algebraic Graph Theory Seminar - Cristina Dalfó

Title: On the Laplacian spectra of token graphs

Speaker: Cristina Dalfó
Affiliation: Universitat de Lleida
Zoom: Contact Soffia Arnadottir

Abstract:

We study the Laplacian spectrum of token graphs, also called symmetric powers of graphs. The k-token graph F_k(G)of a graph G is the graph whose vertices are the k-subsets of vertices from G, two of which being adjacent whenever their symmetric difference is a pair of adjacent vertices in G. In this talk, we give a relationship between the Laplacian spectra of any two token graphs of a given graph.

Monday, December 13, 2021 11:30 am - 11:30 am EST (GMT -05:00)

Algebraic Graph Theory Seminar - Logan Crew

Title: A New Graph Polynomial from the Chromatic Symmetric Function

Speaker: Logan Crew
Affiliation: University of Waterloo
Zoom: Contact Soffia Arnadottir

Abstract:

The chromatic symmetric function X_G of a graph generalizes the chromatic polynomial by distinguishing proper n-colourings by how many times each colour is used. Furthermore, many other natural graph polynomials also arise from specializations of X_G;

Monday, January 10, 2022 11:30 am - 11:30 am EST (GMT -05:00)

Algebraic Graph Theory Seminar - Emanuel Juliano

Title: Quantum walks do not like bridges

Speaker: Emanuel Juliano
Affiliation: Universidade Federal de Minas Gerais
Zoom: Contact Sabrina Lato

Abstract:

In this talk we consider graphs with two cut vertices joined by a bridge, and prove that there can be no quantum perfect state transfer between these vertices, unless the graph has no other vertex.

Thursday, January 13, 2022 1:00 pm - 1:00 pm EST (GMT -05:00)

Algebraic Combinatorics Seminar - Gabriel Frieden

Title: Crystal invariant theory and geometric RSK

Speaker: Gabriel Frieden
Affiliation:

Université du Québec à Montréal (UQAM)

Zoom: Contact Olya Mandelshtam

Abstract:

The original problem of classical invariant theory was to describe the invariants of SL_m acting on a polynomial ring in an m \times n matrix of variables. One way to solve this problem is to consider the polynomial ring as a GL_m \times GL_n representation, and decompose this representation into its irreducible components.