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Monday, March 8, 2021 — 11:30 AM EST
Title: Lexicographic products, wreath products, and generalisations
| Speaker: | Joy Morris |
| Affiliation: | University of Lethbridge |
| Zoom: | Contact Soffia Arnadottir |
Abstract:
I will present a history and overview of some of the work that has been done on the lexicographic product of graphs, and related generalisations. The focus of my talk will be on the automorphism groups of such graphs, and the relationship to the wreath product of permutation groups.
Thursday, March 11, 2021 — 1:00 PM EST
Title: Equivalences of Wilson loop diagrams
| Speaker: | Karen Yeats |
| Affiliation: | University of Waterloo |
| Zoom: | Contact Karen Yeats |
Abstract:
I will talk about Wilson loop diagrams, explain a bit about what they are, and some of the combinatorial questions that come out of them, with a focus on when they are equivalent. This is joint work with Susama Agarwala and Zee Fryer.
Friday, March 12, 2021 — 3:30 PM EST
Title: An approximate solution to a 2,079,471-point traveling salesman problem
| Speaker: | Bill Cook |
| Affliation: | University of Waterloo |
| Zoom: | Please email Emma Watson |
Abstract:
Together with Keld Helsguan, we have found a TSP tour through the 3D positions of 2,079,471 stars. We discuss how linear programming allows us to prove the tour is at most a factor of 0.0000074 longer than an optimal solution. The talk will focus on the use of minimum cuts and GF(2) linear systems, to drive the cutting-plane method towards strong LP relaxations.
Thursday, March 25, 2021 — 1:00 PM EDT
Title: An Efficient Algorithm for Deciding the Vanishing of Schubert Polynomial Coefficients
| Speaker: | Colleen Robichaux |
| Affiliation: | University of Illinois at Urbana-Champaign |
| Zoom: | Contact Karen Yeats |
Abstract:
Schubert polynomials form a basis of all polynomials and appear in the study of cohomology rings of flag manifolds. The vanishing problem for Schubert polynomials asks if a coefficient of a Schubert polynomial is zero. We give a tableau criterion to solve this problem, from which we deduce the first polynomial time algorithm. These results are obtained from new characterizations of the Schubitope, a generalization of the permutahedron defined for any subset of the n x n grid. In contrast, we show that computing these coefficients explicitly is #P-complete. This is joint work with Anshul Adve and Alexander Yong.