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Monday, April 3, 2023 3:00 pm - 3:00 pm EDT (GMT -04:00)

Graph and Matroids Seminar - Alvaro Carbonero

Title: The heroes of digraphs: coloring digraphs with forbidden induced subgraphs

Speaker: Alvaro Carbonero
Affiliation: University of Waterloo
Location: MC 5479

Abstract: The chromatic number is one of the most studied graph invariants in graph theory. $\chi$-boundedness, for instance, studies the induced subgraphs present in graphs with large chromatic number and small clique number. Neumann-Lara introduced an analog directed version of this graph invariant: the dichromatic number of digraphs.

Monday, April 10, 2023 11:30 am - 11:30 am EDT (GMT -04:00)

Algebraic Graph Theory - Andrew Jena

Title: Quantum Algorithms and Mutually Unbiased Bases

Speaker: Andrew Jena
Affiliation: University of Waterloo
Location: Please contact Sabrina Lato for Zoom link

Abstract: Mutually unbiased bases are fundamental to quantum information theory, showing up in quantum key distribution, quantum error correction, and quantum entanglement measures. They likewise might be familiar to algebraic graph theorists, thanks to their connection to equiangular lines and association schemes.

Friday, April 14, 2023 3:30 pm - 3:30 pm EDT (GMT -04:00)

Tutte Colloquium - Peter Winkler

Title: Sets that Support a Joint Distribution

Speaker: Peter Winkler
Affiliation: Dartmouth College
Location: MC 5501 or contact Eva Lee for Zoom link

Abstract: Given a closed set on the plane and two probability distributions on the real line, when are there random variables with the given distributions whose joint distribution is supported by the given set?

Monday, April 24, 2023 11:30 am - 11:30 am EDT (GMT -04:00)

Algebraic Graph Theory - Nathan Benedetto Proenca

Title: A Primal-Dual Extension of the Goemans and Williamson Algorithm for Weighted Fractional Cut Cover

Speaker: Nathan Benedetto Proenca
Affiliation: University of Waterloo
Location: Please contact Sabrina Lato for Zoom link

Abstract: A cut in a graph G = (V, E) is a set of edges which has one endpoint in S, for a given subset S of V. The fractional cut-covering number is the optimal value of a linear programming relaxation for the problem of covering each edge by a set of cuts. Beyond its role as part of Šámal's work on cut continuous functions, this graph parameter also arises as the gauge dual of the maximum cut problem.

Monday, May 1, 2023 11:30 am - 11:30 am EDT (GMT -04:00)

Algebraic Graph Theory - Sjanne Zeijlemaker

Title: On the diameter and zero forcing number of some graph classes in the Johnson, Grassmann and Hamming association scheme

Speaker: Sjanne Zeijlemaker
Affiliation:

Eindhoven University of Technology

Location: Please contact Sabrina Lato for Zoom link

Abstract:  Graph classes in the Johnson, Grassmann and Hamming association scheme have received a considerable amount of attention over the last decades. Although several (NP-hard) graph parameters have been investigated for these families, many remain unknown. In this talk, we establish the diameter of generalized Grassmann graphs, extending previous results for generalized Johnson graphs.

Monday, May 15, 2023 11:30 am - 11:30 am EDT (GMT -04:00)

Algebraic Graph Theory - Yuval Filmus

Title: Orthogonal basis of eigenvectors for the Johnson and Kneser graphs

Speaker: Yuval Filmus
Affiliation: Technion
Location: Please contact Sabrina Lato for Zoom link

Abstract: The Johnson and Kneser graphs have the same eigenspaces. How explicitly can we describe these eigenspaces? 

Monday, May 15, 2023 1:00 pm - 1:00 pm EDT (GMT -04:00)

C&O Reading Group - Jacob Skitsko

Title: The matching polytope has exponential extension complexity

Speaker: Jacob Skitsko
Affiliation: University of Waterloo
Location: MC 6029

Abstract: This Friday we will build off of some previous results by looking at the paper “The matching polytope has exponential extension complexity” by Thomas Rothvoss! At the beginning of the semester, we saw that the matching (and TSP) polytopes cannot be expressed by a polynomial sized symmetric LP.

Monday, May 15, 2023 2:30 pm - 2:30 pm EDT (GMT -04:00)

Seminar - Douglas Stebila

Title: A brief introduction to lattice-based cryptography

Speaker: Douglas Stebila
Affiliation: University of Waterloo
Location: MC 5479

Abstract: A brief introduction to lattice-based cryptography, one of the leading candidates for building quantum-resistant cryptosystems.

Thursday, May 18, 2023 3:00 pm - 3:00 pm EDT (GMT -04:00)

Graphs and Matroids Seminar - Jerónimo Valencia Porras

Title: Snake decomposition of lattice path matroids

Speaker: Jerónimo Valencia Porras 
Affiliation: University of Waterloo
Location: MC 5501

Abstract: Lattice path matroids (LPMs) are positroids whose base polytopes have a nice decomposition. We provide a geometric perspective to this decomposition in terms of fences and their order polytopes, which correspond to a certain class of LPMs we call snakes.

Friday, May 19, 2023 3:30 pm - 3:30 pm EDT (GMT -04:00)

Distinguished Tutte Lecture - Petter Brändén

Title: Lorentzian polynomials

Speaker: Petter Brändén
Affiliation: KTH Royal Institute of Technology
Location: MC 5501 

Abstract: Lorentzian polynomials on cones are intimately connected to Hodge theory, matroid theory and the geometry of zeros of polynomials.