Contact Info
Combinatorics & Optimization
University of Waterloo
Waterloo, Ontario
Canada N2L 3G1
Phone: 519-888-4567, ext 33038
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Monday, October 2, 2023 11:30 AM EDT
Title: Neumaier graphs
| Speaker: | Maarten De Boeck |
| Affiliation: | University of Memphis |
| Location: | Please contact Sabrina Lato for Zoom link |
Abstract: A Neumaier graph is an edge-regular graph with a regular clique. Several families of strongly regular graphs (but not all of them) are indeed Neumaier, but in 1981 it was asked whether there are Neumaier graphs that are not strongly regular. This question was only solved a few years ago by Greaves and Koolen, so now we know there are so-called strictly Neumaier graphs.
Thursday, October 5, 2023 2:00 PM EDT
Title: Diagrammatic boundary calculus for Wilson loop diagrams
| Speaker: | Karen Yeats |
| Affiliation: | University of Waterloo |
| Location: | MC 6029 |
There will be a pre-seminar presenting relevant background at the beginning graduate level starting at 1pm.
Abstract: This talk is about a different part of the quantum field theory story than I usually talk about. Wilson loop diagrams can be used to index amplitudes in a theory known as N=4 SYM. Suitably nice Wilson loop diagrams are also associated to positroids. For both mathematical and physical reasons it would be nice to have a diagrammatic understanding of the boundaries of the positroid cells of all co-dimensions. While we do not yet have a full understanding, we can build many boundaries with certain diagrammatic moves.
Joint work with Susama Agarwala and Colleen Delaney.
Thursday, October 5, 2023 3:00 PM EDT
Title: A closure lemma for tough graphs and Hamiltonian ideals
| Speaker: | Chinh T. Hoang |
| Affiliation: | Wilfrid Laurier University |
| Location: | MC 5417 |
Abstract: The closure of a graph $G$ is the graph $G^*$ obtained from $G$ by repeatedly adding edges between pairs of non-adjacent vertices whose degree sum is at least $n$, where $n$ is the number of vertices of $G$. The well-known Closure Lemma proved by Bondy and Chv\'atal states that a graph $G$ is Hamiltonian if and only if its closure $G^*$ is. This lemma can be used to prove several classical results in Hamiltonian graph theory. We prove a version of the Closure Lemma for tough graphs.
Friday, October 6, 2023 3:30 PM EDT
Title: Kissing Polytopes
| Speaker: | Antoine Deza |
| Affiliation: | McMaster University |
| Location: | MC 5501 |
Abstract: We investigate the following question: how close can two disjoint lattice polytopes contained in a fixed hypercube be? This question stems from various contexts where the minimal distance between such polytopes appears in complexity bounds of optimization algorithms.