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Monday, October 17, 2022 11:30 am - 11:30 am EDT (GMT -04:00)

Algebraic Graph Theory Seminar - Harmony Zhan

Title: An introduction to discrete quantum walks

Speaker: Harmony Zhan
Affiliation: Simon Fraser University
Location: please contact Sabrina Lato for Zoom link

Abstract: A discrete quantum walk is determined by a unitary matrix representation of a graph. In this talk, I will give an overview of different quantum walks, and show how the spectral information of the unitary matrix representation links properties of the walks to properties of the graphs. Part of this talk will be based on the book, Discrete Quantum Walks on Graphs and Digraphs, by Chris and me.

Thursday, October 20, 2022 1:00 pm - 1:00 pm EDT (GMT -04:00)

Algebraic Combinatorics Seminar - Sheila Sundaram

Title: Quasisymmetric functions,  descent sets, immaculate tableaux, and 0-Hecke modules

Speaker: Shelia Sundaram
Affiliation:  
Location: MC 5479 or contact Olya Mandelshtam for Zoom link

Abstract:

The first half of this talk will be expository and devoted to a discussion of (quasi)symmetric functions and tableaux.

We define new families of quasisymmetric functions, in particular the new basis of row-strict dual immaculate functions, with an associated cyclic, indecomposable 0-Hecke algebra module. Our row-strict immaculate functions are related to the dual immaculate functions of Berg-Bergeron-Saliola-Serrano-Zabrocki (2014-15) by the involution \psi on the ring Qsym of quasisymmetric functions. We uncover the remarkable properties of the immaculate Hecke poset induced by the 0-Hecke action on standard immaculate tableaux, revealing other submodules and quotient modules, often cyclic and indecomposable.

Friday, October 21, 2022 12:00 pm - 12:00 pm EDT (GMT -04:00)

Combinatorial Optimization Reading Group - Noah Weninger

Title: The Probabilistic Set-Covering Problem

Speaker: Noah Weninger
Affiliation: University of Waterloo
Location: MC 6026 or contact Rian Neogi for Zoom link

Abstract: In the classical set-covering problem, we have a set of items and a set S of subsets of the items. The objective is to find a min-cost subset C of S which covers every item, i.e., where every item is contained in at least one of the subsets in C. The probabilistic set-covering problem (PSC) generalizes this to a stochastic setting where the objective is to find a min-cost covering which covers a random subset of the items with probability at least p. We will discuss some structural properties of this problem which lead to a branch-and-bound algorithm for solving it.

Monday, October 24, 2022 11:30 am - 11:30 am EDT (GMT -04:00)

Algebraic Graph Theory Seminar - Guillermo Nunez Ponasso

Title: Hadamard’s Maximal Determinant Problem and Generalisations

Speaker: Guillermo Nunez Ponasso
Affiliation: Worcester Polytechnic Institute
Location: Please contact Sabrina Lato for Zoom link

Abstract:  Any matrix $M$ of order $n$ with entries taken from the complex unit disk satisfies Hadamard’s determinantal inequality $|\det M|\leq n^{n/2}$. Matrices meeting this bound with equality have pairwise orthogonal rows and columns. Such matrices are known as Hadamard matrices, and character tables of finite abelian groups give examples at every order.

Thursday, October 27, 2022 1:00 pm - 1:00 pm EDT (GMT -04:00)

Algebraic Combinatorics Seminar - Anna Pun

Title: A raising operator formula for Macdonald polynomials

Speaker: Anna Pun
Affiliation: CUNY- Baruch College
Location: MC 5479 or contact Olya Mandelshtam for Zoom

Abstract: In this talk, I will give a brief introduction on Catalanimal, a tool that helps us to prove the shuffle theorem under any line, the extended delta conjecture and the Loehr- Warrington conjecture. I will then focus on its variant "Macanimal" which gives us an explicit raising operator formula for the modified Macdonald polynomials. Our method just as easily yields a formula for an infinite series of $GL_l$ characters which truncates to the modified Macdonald polynomials.

Friday, October 28, 2022 12:00 pm - 12:00 pm EDT (GMT -04:00)

Combinatorial Optimization Reading Group - Sharat Ibrahimpur

Title: Stochastic Minimum Norm Combinatorial Optimization

Speaker: Sharat Ibrahimpur
Affiliation:  
Location: MC 6029 or contact Rian Neogi for Zoom link

Abstract: In this work, we introduce and study stochastic minimum-norm optimization. We have an underlying combinatorial optimization problem where the costs involved are random variables with given distributions; each feasible solution induces a random multidimensional cost vector. The goal is to find a solution that minimizes the expected norm of the induced cost vector, for a given monotone, symmetric norm.

Friday, October 28, 2022 3:30 pm - 3:30 pm EDT (GMT -04:00)

Tutte Colloquium - Jonathan Eckstein

Title: The ADMM:  Past, Present, and Future

Speaker: Jonathan Eckstein
Affiliation: Rutgers University
Location: MC 5501 or contact Melissa Cambrdige for Zoom link

Abstract: Over the past 15 years, the alternating direction method of multipliers (ADMM) has become a standard optimization method.  This talk will cover the origins of the ADMM, its subsequent development, and what to expect in the future.

Monday, October 31, 2022 11:30 pm - 11:30 pm EDT (GMT -04:00)

Algebraic Graph Theory Seminar - Ingemar Bengtsson

Title: Equiangular lines and algebraic number theory

Speaker: Ingemar Bengtsson
Affiliation: Stockholm University
Location: contact Sabrina Lato for Zoom link

Abstract: It is believed that SICs, that is maximal equiangular tight frames, exist in all complex vector spaces. To construct them we use the Weyl-Heisenberg groups, and hence the cyclotomic numbers (roots of unity).

Thursday, November 3, 2022 1:00 pm - 1:00 pm EDT (GMT -04:00)

Algebraic Combinatorics Seminar - Jeremy Chizewer

Title: The Hat Guessing Number of Graphs

Speaker: Jeremy Chizewer
Affiliation: University of Waterloo
Location: MC 5479 in person

Abstract:  The hat guessing number HG(G) of a graph G on n vertices is defined in terms of the following game: n players are placed on the n vertices of G, each wearing a hat whose color is arbitrarily chosen from a set of q possible colors. Each player can see the hat colors of his neighbors, but not his own hat color. All of the players are asked to guess their own hat colors simultaneously, according to a predetermined guessing strategy and the hat colors they see, where no communication between them is allowed.