Contact Info
Combinatorics & Optimization
University of Waterloo
Waterloo, Ontario
Canada N2L 3G1
Phone: 519-888-4567, ext 33038
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Monday, March 27, 2023 — 8:00 PM EDT
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 EDT
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 EDT
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".