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Friday, March 24, 2023 3:30 pm - 3:30 pm EDT (GMT -04:00)

Tutte Colloquium - David Gosset

Title: On the complexity of quantum partition functions

Speaker: David Gosset
Affiliation: University of Waterloo
Location: MC 5501 or contact Eva Lee for Zoom link

Abstract: Quantum complexity theory has been intertwined with the study of quantum many-body systems ever since Kitaev's insight that computing their ground energies is an intractable quantum constraint satisfaction problem that is complete for a quantum generalization of NP.

Monday, March 27, 2023 8:00 pm - 8:00 pm EDT (GMT -04:00)

Algebraic Graph Theory Seminar - Jephian C.-H. Lin

Title: Inverse eigenvalue problem of a graph

Speaker: Jephian C.-H. Lin
Affiliation: National Sun Yat-sen University
Location: Please contact Sabrina Lato for Zoom link

Abstract:  We often encounter matrices whose pattern (zero-nonzero, or sign) is known while the precise value of each entry is not clear. Thus, a natural question is what we can say about the spectral property of matrices of a given pattern. When the matrix is real and symmetric, one may use a simple graph to describe its off-diagonal nonzero support.

Wednesday, March 29, 2023 2:30 pm - 2:30 pm EDT (GMT -04:00)

Algebraic Graph Theory - Sabrina Lato

Title: Distance-Regular and Distance-Biregular Graphs

Speaker: Sabrina Lato
Affiliation: University of Waterloo
Location: MC

Abstract: For a given diameter d and valency k, what is the maximum number of vertices a k-regular graph of diameter d can have, and what graphs meet that bound? Although there is a straightforward counting argument to bound the number of vertices using the structural information, the problem of characterizing the graphs that meet the bound turns out to be a problem in algebraic graph theory, and helps gives rise to the notion of distance-regular graphs.

Thursday, March 30, 2023 1:00 pm - 1:00 pm EDT (GMT -04:00)

Algebraic Combinatorics Seminar - Freddy Cachazo

Title: Arrangements of Pseudolines, Tropical Grassmannians, and Generalized Scattering Amplitudes

Speaker: Freddy Cachazo
Affiliation: Perimeter Institute
Room: MC 6029

Abstract: For each arrangement of (pseudo)lines on the projective plane, it is possible to construct a differential form that captures its combinatorial structure. The forms have simple poles whenever triangles shrink to a point in the arrangement, and share the same residue when two arrangements are connected via a "triangle flip".

Monday, April 3, 2023 11:30 am - 11:30 am EDT (GMT -04:00)

algebraic Graph Theory - Monu Kadyan

Title: Four types of integrality on mixed Cayley graphs over abelian groups

Speaker: Monu Kadyan
Affiliation: Indian Institute of Technology Guwahati
Location: Please contact Sabrina Lato for Zoom link

Abstract: A mixed graph is called H-integral (resp. HS-integral) if the eigenvalues of its Hermitian-adjacency matrix (resp. Hermitian-adjacency matrix of second kind) are integers.

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.