Events

Filter by:

Limit to events where the first date of the event:
Date range
Limit to events where the first date of the event:
Limit to events where the title matches:
Limit to events where the type is one or more of:
Limit to events tagged with one or more of:
Limit to events where the audience is one or more of:
Friday, June 23, 2023 1:00 pm - 1:00 pm EDT (GMT -04:00)

C&O Special Seminar - Noela Müller

Title: The rank of sparse symmetric matrices over arbitrary fields

Speaker: Noela Müller
Affiliation: TU/e Eindhoven University of Technology
Location: MC 5501

Abstract: Consider a sequence of sparse Erdös-Rényi random graphs (G_{n,d/n})_n on n vertices with edge probability d/n. Moreover, we equip the edges of G_{n,d/n} with prescribed non-zero edge weights chosen from an arbitrary field F.

Monday, June 26, 2023 11:30 am - 11:30 am EDT (GMT -04:00)

Algebraic Graph Theory - Karen Yeats

Title: Diagonal coefficients of Kirchhoff polynomials of 2k-regular graphs and the proof of the c_2 completion conjecture

Speaker: Karen Yeats
Affiliation: University of Waterloo and Perimeter Institute
Location: Please contact Sabrina Lato for Zoom link

Abstract: I have for many years been interested in graph invariants with the same symmetries as the Feynman period. Recently Erik Panzer found a new such invariant coming from a particular coefficient of the Martin polynomial. Together we used this to prove an over 10 year old conjecture on an arithmetic graph invariant known as the c_2 invariant, and came to understand that diagonal coefficients of Kirchhoff polynomials tie together many of the known graph invariants with the symmetries of Feynman periods and unlock previously inaccessible proofs.

Joint work with Erik Panzer.

Thursday, June 29, 2023 3:00 pm - 3:00 pm EDT (GMT -04:00)

Graphs and Matroids Seminar - Jane Gao

Title: Minors of random representable matroid over finite fields

Speaker: Jane Gao
Affiliation: University of Waterloo
Location: MC 5479

Abstract: Consider a random n by m matrix A over GF(q) where every column has k nonzero elements, and let M[A] be the matroid represented by A. In the case that q=2, Cooper, Frieze and Pegden (RSA 2019) proved that given a fixed binary matroid N, if k is sufficiently large, and m/n is sufficiently large (both depending on N), then whp. M[A] contains N as a minor. We improve their result by determining the sharp threshold (of m/n) for the appearance of a fixed q-nary matroid N as a minor of M[A], for every k\ge 3, and every prime q. This is joint work with Peter Nelson.

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

Tutte Colloquium - Andy Zucker

Title: Ramsey degrees, big and small

Speaker: Andy Zucker
Affiliation: University of Waterloo
Location: MC 5501

Abstract: Many of the seminal results in finite Ramsey theory can be phrased by saying that a certain class of finite structures has the Ramsey property, such as the ordinary finite Ramsey theorem (the class of finite linear orders), the dual Ramsey theorem (the class of finite lex-ordered Boolean algebras), the Graham-Leeb-Rothschild theorem (the class of lex-ordered, finite-dimensional vector spaces over a fixed finite field), and the Nesetril-Rodl theorem (the class of finite ordered triangle-free graphs, among many others).

Thursday, July 6, 2023 1:00 pm - 1:00 pm EDT (GMT -04:00)

Algebraic Combinatorics - Ben Webster

Title: Modular representations of the symmetric group and categorification (part I)

Speaker: Ben Webster
Affiliation: University of Waterloo/Perimeter Institute
Location: MC 5501 and Zoom - please contact Oliver Pechenik for the Zoom link

Abstract: I'll give two talks on the representations of the symmetric group over small finite fields, in particular, their block structure, with an emphasis on the perspective from categorical actions of Lie algebras.  No previous background in modular representation theory will be assumed.  

Friday, July 7, 2023 3:30 pm - 3:30 pm EDT (GMT -04:00)

Distinguished Tutte Lecture - Jacob Fox

Title: Ramsey Cayley graphs, random graph models, and information theory

Speaker: Jacob Fox
Affiliation: Stanford University
Location: MC 5501

Abstract: A graph is Ramsey if its largest clique or independent set is of size logarithmic in the number of vertices. While almost all graphs are Ramsey, there is still no known explicit construction of Ramsey graphs. Alon conjectured that every finite group has a Ramsey Cayley graph.

Monday, July 10, 2023 8:00 pm - 8:00 pm EDT (GMT -04:00)

Algebraic Graph Theory - Xiaoye Liang

Title: Thin distance-regular graphs with classical parameters $(D,q,q,\frac{q^{t}-1}{q-1}-1)$ with $t> D$ are the Grassmann graphs

Speaker: Xiaoye Liang
Affiliation: Anhui Jianzhu University
Location: Please contact Sabrina Lato for Zoom link

Abstract: In the survey paper by Van Dam, Koolen and Tanaka (Distance-regular graphs, Electron. J. Comb., Dynamic Survey (2016), \#DS22), they asked to classify the thin $Q$-polynomial distance-regular graphs. In this talk, we will discuss our result which states that the Grassmann graphs with large diameter are characterized by their intersection numbers under the extra condition that they are thin.

This is joint work with Jack Koolen and Ying-Ying Tan.

Monday, July 17, 2023 11:30 am - 11:30 am EDT (GMT -04:00)

Algebraic Graph Theory - Himanshu Gupta

Title: On the eigenvalues of the graphs D(5,q)

Speaker: Himanshu Gupta
Affiliation: University of Delaware
Location: Please contact Sabrina Lato for Zoom link

Abstract: In 1995, Lazebnik and Ustimenko introduced the family of q-regular graphs D(k, q), which is defined for any positive integer k and prime power q. The connected components of the graph D(k, q) have provided the best-known general lower bound on the size of a graph for any given order and girth to this day.

Thursday, July 20, 2023 1:00 pm - 1:00 pm EDT (GMT -04:00)

Algebraic Combinatorics - Li Li

Title: Bipartite determinantal ideals and concurrent vertex maps

Speaker: Li Li
Affiliation: Oakland University
Location: MC 5501

Abstract: The classical determinantal ideals play an important role in commutative algebra, algebraic geometry, representation theory and combinatorics. They can be generalized to bipartite determinantal ideals which are the defining ideals of Nakajima's affine graded quiver variety. In this talk, we will introduce a combinatorial model called concurrent vertex maps to describe the Stanley-Reisner complex of the initial ideal of any bipartite determinantal ideal, and study properties and applications of this model.