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Monday, March 28, 2022 11:30 am - 11:30 am EDT (GMT -04:00)

Algebraic Graph Theory Seminar - Xiaohong Zhang

Title: Oriented Cayley Graphs with all eigenvalues being integer multiples of $\sqrt{\Delta}$

Speaker: Xiaohong Zhang
Affiliation: University of Waterloo
Zoom: Contact Sabrina Lato

Abstract:

Let $G$ be a finite abelian group. An oriented Cayley graph on $G$ is a Cayley digraph $X(G,C)$ such that $C \cap (-C)=\emptyset$. Consider the $(0,1,-1)$ skew-symmetric adjacency matrix of an oriented Cayley graph $X=X(G,C)$.

Tuesday, March 29, 2022 3:00 pm - 3:00 pm EDT (GMT -04:00)

Graphs and Matroids Seminar - Zishen Qu

Title: Minimal induced subgraphs of two classes of 2-connected non-Hamiltonian graphs

Speaker: Zishen Qu
Affiliation: University of Waterloo
Zoom: http://matroidunion.org/?page_id=2477 or contact Shayla Redlin

Abstract:

Finding sufficient conditions for a class of graphs to be Hamiltonian is an old problem, with a wide variety of conditions such as Dirac's degree condition and Whitney's theorem on 4-connected planar triangulations. We discuss some past results on sufficient conditions for Hamiltonicity involving the exclusion of fixed induced subgraphs, and some properties of the graphs involved in such results.

Thursday, March 31, 2022 1:00 pm - 1:00 pm EDT (GMT -04:00)

Algebraic Combinatorics Seminar - Laura Colmenarejo

Title: Multiplying quantum Schubert polynomials using combinatorics

Speaker: Laura Colmenarejo
Affiliation: NC State University
Zoom: Contact Logan Crew or Olya Mandelshtam

Abstract:

Schubert polynomials are a very interesting family of polynomials in algebraic geometry due to their relation with the cohomology of the flag variety. Moreover, they are also very interesting from a combinatorial point of view because they can be considered generalizations of Schur functions. 

Friday, April 1, 2022 3:30 pm - 3:30 pm EDT (GMT -04:00)

Tutte Colloquium - Curtis Bright

Title: SAT Solving with Computer Algebra for Combinatorics

Speaker: Curtis Bright
Affiliation: University of Windsor and Carleton University
Location: MC 5501 or please contact Emma Watson for Zoom link

Abstract:

This talk will describe a method of solving combinatorial problems by coupling Boolean satisfiability (SAT) solvers with computer algebra systems (CASs), thereby combining the search and learning power of SAT solvers with the expressiveness and mathematical sophistication of CASs. 

Tuesday, April 5, 2022 11:30 am - 11:30 am EDT (GMT -04:00)

Algebraic Graph Theory Seminar - Nathan Lindzey

Title: Yet Another Proof of the Erdős-Ko-Rado Theorem

Speaker: Nathan Lindzey
Affiliation: University of Colorado, Boulder
Zoom: Contact Sabrina Lato

Abstract:

We give a short new algebraic proof of the Erdős-Ko-Rado theorem, that for k < n/2, the largest families of k-sets of an n-element set such that any two of its members intersect are precisely those families composed of all k-sets that contain some fixed element.

Tuesday, April 5, 2022 3:00 pm - 3:00 pm EDT (GMT -04:00)

Graphs and Matroids Seminar - Lise Turner

Title: A local version of Hadwiger’s Conjecture

Speaker: Lise Turner
Affiliation: University of Waterloo
Zoom: http://matroidunion.org/?page_id=2477 or contact Shayla Redlin

Abstract:

In 1943, Hadwiger famously conjectured that graphs with no $K_t$ minors are $t-1$ colourable. There has also been significant interest in several variants of the problem, such as list colouring or only forbidding certain classes of minors.

Thursday, April 7, 2022 1:00 pm - 1:00 pm EDT (GMT -04:00)

Algebraic Combinatorics Seminar - Farid Aliniaeifard

Title: Modular relations between chromatic symmetric functions

Speaker: Farid Aliniaeifard
Affiliation: University of British Columbia
Zoom: Contact Logan Crew or Olya Mandelshtam

Abstract:

In 1995, Stanley introduced the chromatic symmetric functions. The study of chromatic symmetric functions of graphs inspired two main research directions.

Monday, April 11, 2022 11:30 am - 11:30 am EDT (GMT -04:00)

Algebraic Graph Theory Seminar - Victor Wang

Title: Deletion-contraction for a unified Laplacian and applications

Speaker: Victor Wang
Affiliation: University of British Columbia
Zoom: Contact Sabrina Lato

Abstract:

We define a graph Laplacian with vertex weights in addition to the more classical edge weights, which unifies the combinatorial Laplacian and the normalised Laplacian.

Tuesday, April 12, 2022 3:00 pm - 3:00 pm EDT (GMT -04:00)

Graphs and Matroids Seminar - Carolyn Chun

Title: Lattice path matroids, lattice path polymatroids, and excluded minors

Speaker: Carolyn Chun
Affiliation: US Naval Academy
Zoom: http://matroidunion.org/?page_id=2477 or contact Shayla Redlin

Abstract:

We define lattice path matroids, polymatroids, Boolean polymatroids, and lattice path polymatroids, which are a subclass of Boolean polymatroids. 

Wednesday, April 13, 2022 2:00 pm - 2:00 pm EDT (GMT -04:00)

Reading Group Talk - Sean Kafer

Title: Generating Short Monotone Paths in 0/1 LPs: From Circuits to Simplex

Speaker: Sean Kafer
Affiliation: University of Waterloo
Zoom: 945 0789 9910 (passcode: kafer)

Abstract: 

Even after decades of study, it is unknown whether there exists a pivot rule for the Simplex method that always solves an LP with only a polynomial number of pivots.  This remains unknown even in the special case of 0/1 LPs - i.e., LPs defined over 0/1 polytopes - a case that includes many extensively studied problems in combinatorial optimization.