Talk_id  Date  Speaker  Title 
29089

Thursday 8/26 2:30 PM

Deanna Needell, UCLA

On the topic of topic modeling: enhancing machine learning approaches with topic features
 Deanna Needell, UCLA
 On the topic of topic modeling: enhancing machine learning approaches with topic features
 08/26/2021
 2:30 PM  2:30 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Olga Turanova (turanova@msu.edu)
In this talk we touch on several problems in machine learning that can benefit from the use of topic modeling. We present topic modeling based approaches for online prediction problems, computer vision, text generation, and others. While these problems have classical machine learning approaches that work well, we show that by incorporating contextual information via topic features, we obtain enhanced and more realistic results. These classical methods include nonnegative matrix and tensor factorization, generative adversarial networks, and even traditional epidemiological SIR models for prediction. In this talk we provide a brief overview of these problems and show how topic features can be used in these settings. We include supporting theoretical and experimental evidence that showcases the broad use of our approaches.

29090

Thursday 9/2 4:30 AM

Jonathan Scarlett, National University of Singapore

Beyond Sparsity: Compressive Sensing with (Deep) Generative Modeling Assumptions
 Jonathan Scarlett, National University of Singapore
 Beyond Sparsity: Compressive Sensing with (Deep) Generative Modeling Assumptions
 09/02/2021
 4:30 AM  5:30 AM
 Online (virtual meeting)
(Virtual Meeting Link)
 Olga Turanova (turanova@msu.edu)
The problem of estimating an unknown vector from linear measurements has a long history in statistics, machine learning, and signal processing. Classical studies focus on the "n >> p" regime (#measurements >> #parameters), and more recent studies handle the "n << p" regime by exploiting lowdimensional structure such as sparsity or lowrankness. Such variants are commonly known as compressive sensing.
In this talk, I will overview recent methods that move beyond these simple notions of structure, and instead assume that the underlying vector is wellmodeled by a generative model (e.g., produced by deep learning methods such as GANs). I will highlight algorithmic works that demonstrated up to 510x savings in the number of measurements over sparsitybased methods, and then move on to our theoretical work characterizing the orderoptimal sample complexity in terms of quantities such as (i) the Lipschitz constant of the model, or (ii) the depth/width in a neural network model. I will also briefly highlight some recent results on nonlinear observation models.

29102

Friday 9/3 3:00 PM

Joshua Ruiter, MSU

Organizing meeting for student algebra seminar
 Joshua Ruiter, MSU
 Organizing meeting for student algebra seminar
 09/03/2021
 3:00 PM  4:00 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Joshua Ruiter (ruiterj2@msu.edu)
We'll discuss plans for the student algebra seminar this semester, e.g. choosing our first few speakers.

29103

Tuesday 9/7 4:00 PM

Sucharit Sarkar, UCLA

Link Floer spectrum via grid diagrams
 Sucharit Sarkar, UCLA
 Link Floer spectrum via grid diagrams
 09/07/2021
 4:00 PM  5:00 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Honghao Gao (gaohongh@msu.edu)
Link Floer homology of links in S^3 can be computed as the homology of a grid chain complex defined using grid diagrams. I will describe a construction of a CW spectrum whose cells correspond to the generators of the grid chain complex, and whose cellular chain complex is the grid chain complex (and therefore, the homology is link Floer homology). This is joint with Ciprian Manolescu.

29100

Wednesday 9/8 3:00 PM

Emily Gunawan, Oklahoma University

Boxball systems and RobinsonSchenstedKnuth tableaux
 Emily Gunawan, Oklahoma University
 Boxball systems and RobinsonSchenstedKnuth tableaux
 09/08/2021
 3:00 PM  3:50 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Bruce E Sagan (bsagan@msu.edu)
The RobinsonSchensted (RS) correspondence is a famous bijection between permutations and pairs (P,Q) of standard tableaux of the same shape, called the RS partition. The RS partition and its conjugate record certain permutation statistics called Greene’s theorem statistics.
A boxball system is a discrete dynamical system which can be thought of as a collection of time states. A permutation on n objects gives a boxball system state by assigning its oneline notation to n consecutive boxes. After a finite number of steps, a boxball system will reach a steady state. From any steady state, we can construct a tableau (not necessarily standard) called the soliton decomposition. The shape of the soliton decomposition is called the BBS partition. An exciting discovery (made in 2019 by Lewis, Lyu, Pylyavskyy, and Sen) is that the BBS partition and its conjugate record a localized version of Greene’s theorem statistics.
We will discuss a few new results:
(1) The Q tableau of a permutation completely determines the dynamics of the corresponding boxball system.
(2) The permutations whose BBS partitions are Lshaped have steadystate time at most 1. This large class of permutations include column reading words and noncrossing involutions.
(3) If the soliton decomposition of a permutation is a standard tableau or if its BBS partition coincides with its RS partition, then its soliton decomposition and its P tableau are equal.
(4) Finally, we study the permutations whose P tableaux and soliton decompositions coincide and refer to them as “good". These “good” permutations are closed under consecutive pattern containment. Furthermore, we conjecture that the “good” Q tableaux are counted by the Motzkin numbers.
This talk is based on REU projects with Ben Drucker, Eli Garcia, Aubrey Rumbolt, Rose Silver (UConn Math REU 2020) and Marisa Cofie, Olivia Fugikawa, Madelyn Stewart, David Zeng (SUMRY 2021).

29098

Wednesday 9/8 4:00 PM

Alexander Volberg, MSU

Drastic differences between the potential theories on trees and on multitrees
 Alexander Volberg, MSU
 Drastic differences between the potential theories on trees and on multitrees
 09/08/2021
 4:00 PM  5:00 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Dapeng Zhan (zhan@msu.edu)
No abstract available.

29094

Thursday 9/9 2:30 PM

Anna Ma, University of California, Irvine

The Kaczmarz Algorithm: Greed, Randomness, and Tensors
 Anna Ma, University of California, Irvine
 The Kaczmarz Algorithm: Greed, Randomness, and Tensors
 09/09/2021
 2:30 PM  3:30 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Olga Turanova (turanova@msu.edu)
The Kaczmarz algorithm is an iterative method for solving linear systems of equations of the form Ax=y. Owing to its low memory footprint, the Kaczmarz algorithm has gained popularity for its practicality in applications to largescale data, acting only on single rows of A at a time. In this talk, we discuss selecting rows of A randomly (Randomized Kaczmarz), selecting rows in a greedy fashion (Motzkin's Method), and selecting rows in a partially greedy fashion (Sampling KaczmarzMotzkin algorithm). Despite their variable computational costs, these algorithms have been proven to have the same theoretical upper bound on the convergence rate. Here we present an improvement upon previous known convergence bounds of the Sampling KaczmarzMotzkin algorithm, capturing the benefit of partially greedy selection schemes. Time permitting, we also will discuss an extension of the Kaczmarz algorithm to the setting where data takes on the form of a tensor and make connections between the new Tensor Kaczmarz algorithm and previously established algorithms. This presentation contains joint work with Jamie Haddock and Denali Molitor.

29104

Friday 9/10 3:00 PM

Joshua Ruiter, MSU

Abstract representations of special unitary groups
 Joshua Ruiter, MSU
 Abstract representations of special unitary groups
 09/10/2021
 3:00 PM  4:00 PM

(Virtual Meeting Link)
 Joshua Ruiter (ruiterj2@msu.edu)
We'll discuss the background material for the main result of the following paper: https://arxiv.org/abs/2107.07351. We'll start by talking about quasisplit special unitary groups and the associated Steinberg groups. If we have time, we'll talk about algebraic rings. This will be the first in a sequence of two talks on this paper.

29110

Tuesday 9/14 11:10 AM

Matthew Lorentz, Michigan State University

Derivations and the Hochschild Cohomology of Uniform Roe Algebras, Part 1
 Matthew Lorentz, Michigan State University
 Derivations and the Hochschild Cohomology of Uniform Roe Algebras, Part 1
 09/14/2021
 11:10 AM  12:00 PM
 C304 Wells Hall
 Brent Nelson (banelson@msu.edu)
In this series of talks we show a necessary and sufficient condition for the vanishing of the Hochschild cohomology of a uniform Roe algebra. Specifically, the ndimensional continuous Hochschild cohomology vanishes if and only if every norm continuous nlinear map from the uniform Roe algebra to itself is equivalent to a weakly continuous nlinear map.
In our first talk we will begin defining and discussing derivations as they are an important building block of Hochschild cohomology. Motivated by the needs of mathematical physics and the study of oneparameter automorphism groups, it is interesting to study whether all derivations are inner (i.e. given by the commutator bracket) for a particular C*algebra. In the 1970s, a complete solution to this problem was obtained in the separable case via the work of several authors. For nonseparable C*algebras the picture is murkier. Our main goal in this talk is to give a new class of examples that only have inner derivations: uniform Roe algebras, which are separable only in the trivial finite dimensional case. Uniform Roe algebras were originally introduced for indextheoretic purposes but are now studied for their own sake as a bridge between C*algebra theory and coarse geometry, as well as having interesting applications to single operator theory. Lastly, we will briefly explain how the uniform Roe algebra only having inner derivations is equivalent to the first Hochschild cohomology vanishing.

29101

Tuesday 9/14 4:00 PM

Peter Johnson, UVA

A zero surgery obstruction from involutive Heegaard Floer homology
 Peter Johnson, UVA
 A zero surgery obstruction from involutive Heegaard Floer homology
 09/14/2021
 4:00 PM  5:00 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Honghao Gao (gaohongh@msu.edu)
A fundamental result in 3manifold topology due to Lickorish and Wallace says that every closed oriented connected 3manifold can be realized as surgery on a link in the 3sphere. One may therefore ask: which 3manifolds can be obtained by surgery on a link with a single component, i.e. a knot, in the 3sphere? More specifically, one can ask: which 3manifolds are obtained by zero surgery on a knot in the 3sphere? In this talk, we give a brief outline of some known results to this question in the context of small Seifert fibered spaces. We then sketch a new method, using involutive Heegaard Floer homology, to show that certain 3manifolds cannot be obtained by zero surgery on a knot in the three sphere. In particular, we produce a new infinite family of weight 1 irreducible small Seifert fibered spaces with first homology Z which cannot be obtained by zero surgery on a knot in the 3sphere, extending a result of Hedden, Kim, Mark and Park.

29114

Wednesday 9/15 3:00 PM

Oliver Pechenik, University of Waterloo

What is the degree of a Grothendieck polynomial?
 Oliver Pechenik, University of Waterloo
 What is the degree of a Grothendieck polynomial?
 09/15/2021
 3:00 PM  3:50 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Bruce E Sagan (bsagan@msu.edu)
Jenna Rajchgot observed that the CastelnuovoMumford regularity of matrix Schubert varieties is computed by the degrees of the corresponding Grothendieck polynomials. We give a formula for these degrees. Indeed, we compute the leading terms of the top degree pieces of Grothendieck polynomials and give a complete description of when two Grothendieck polynomials have the same top degree piece (up to scalars). Our formulas rely on some new facts about major index of permutations. (Joint work with David Speyer and Anna Weigandt.)

29099

Wednesday 9/15 4:00 PM

Kleinhenz, Perry, MSU

Stabilization rates for the damped wave equation with polynomial and oscillatory damping
 Kleinhenz, Perry, MSU
 Stabilization rates for the damped wave equation with polynomial and oscillatory damping
 09/15/2021
 4:00 PM  5:00 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Dapeng Zhan (zhan@msu.edu)
In this talk I will discuss energy decay of solutions of the Damped wave equation. After giving an overview of classical results I'll focus on the torus with damping that does not satisfy the geometric control condition. In this setup properties of the damping at the boundary of its support determine the decay rate, however a general sharp rate is not known.
I will discuss damping which is 0 on a strip and vanishes either like a polynomial x^b or an oscillating exponential e^{1/x} sin^2(1/x). Polynomial damping produces decay of the semigroup at exactly t^{(b+2)/(b+3)}, while oscillating damping produces decay at least as fast as t^{4/5+\delta} for any \delta>0. I will explain how these model cases are proved and how they direct further study of the general sharp rate.

29107

Wednesday 9/15 4:00 PM

Yoonjoo Kim, Stony Brook University

The dual Lagrangian fibration of compact hyperKahler manifolds
 Yoonjoo Kim, Stony Brook University
 The dual Lagrangian fibration of compact hyperKahler manifolds
 09/15/2021
 4:00 PM  5:00 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Laure Flapan (flapanla@msu.edu)
A compact hyperKahler manifold is a higher dimensional generalization of a K3 surface. An elliptic fibration of a K3 surface correspondingly generalizes into the socalled Lagrangian fibration of a compact hyperKahler manifold. It is known that an elliptic fibration of a K3 surface is always "selfdual" in a certain sense. This turns out to be not the case for higherdimensional Lagrangian fibrations. In this talk, we will explicitly construct the dual of Lagrangian fibrations of all currently known examples of compact hyperKahler manifolds.
Passcode: MSUALG

29095

Thursday 9/16 2:30 PM

Russell Luke, University of Göttingen

Structured (In)Feasibility: Nonmonotone Operator Splitting in Nonlinear Spaces
 Russell Luke, University of Göttingen
 Structured (In)Feasibility: Nonmonotone Operator Splitting in Nonlinear Spaces
 09/16/2021
 2:30 PM  3:30 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Olga Turanova (turanova@msu.edu)
The success of operator splitting techniques for convex optimization has led to an explosion of methods for solving largescale and nonconvex optimization problems via convex relaxation. This success is at the cost of overlooking direct approaches to operator splitting that embrace some of the more inconvenient aspects of many model problems, namely nonconvexity, nonsmoothness and infeasibility. I will introduce some of the tools we have developed for handling these issues, and present sketches of the basic results we can obtain. The formalism is in general metric spaces, but most applications have their basis in Euclidean spaces. Along the way I will try to point out connections to other areas of intense interest, such as optimal mass transport.

29159

Thursday 9/16 3:00 PM

Chen Zhang, Michigan State University

An introduction to Instanton Floer homology
 Chen Zhang, Michigan State University
 An introduction to Instanton Floer homology
 09/16/2021
 3:00 PM  4:00 PM
 C304 Wells Hall
 Danika Keala Van Niel ()
Instanton Floer homology is a threemanifold invariant connected to Donaldson theory introduced by Floer himself which turns out to be a powerful tool to study 3manifolds. In today’s talk, I will first briefly review the (ordinary) Morse background and to introduce basic notions about connections. Then we will see the definition and basic properties of the ChernSimons invariant, and a sketch of the construction of the instanton homology of a homology 3sphere. Lastly, we will see some applications of the Instanton Floer homology and some other versions of Instanton Floer homology if time permits.

29118

Friday 9/17 3:00 PM

Joshua Ruiter, MSU

Algebraic rings
Building on what we discussed last week, I'll talk about how to associate an algebraic ring to an abstract representation of a special unitary group.

29131

Tuesday 9/21 11:10 AM

Matthew Lorentz, Michigan State University

Derivations and the Hochschild Cohomology of Uniform Roe Algebras, Part 2
 Matthew Lorentz, Michigan State University
 Derivations and the Hochschild Cohomology of Uniform Roe Algebras, Part 2
 09/21/2021
 11:10 AM  12:00 PM
 C304 Wells Hall
 Brent Nelson (banelson@msu.edu)
In this series of talks we show a necessary and sufficient condition for the vanishing of the Hochschild cohomology of a uniform Roe algebra. Specifically, the ndimensional continuous Hochschild cohomology vanishes if and only if every norm continuous nlinear map from the uniform Roe algebra to itself is equivalent to a weakly continuous nlinear map.
In our second talk we will continue discussing derivations as they are an important building block of Hochschild cohomology. Motivated by the needs of mathematical physics and the study of oneparameter automorphism groups, it is interesting to study whether all derivations are inner (i.e. given by the commutator bracket) for a particular C*algebra. In the 1970s, a complete solution to this problem was obtained in the separable case via the work of several authors. For nonseparable C*algebras the picture is murkier. Our main goal in this talk is to give a new class of examples that only have inner derivations: uniform Roe algebras, which are separable only in the trivial finite dimensional case. Uniform Roe algebras were originally introduced for indextheoretic purposes but are now studied for their own sake as a bridge between C*algebra theory and coarse geometry, as well as having interesting applications to single operator theory. We will then briefly explain how the uniform Roe algebra only having inner derivations is equivalent to the first Hochschild cohomology vanishing. Lastly, we will discuss the Hochschild cohomology in higher dimensions.

29120

Tuesday 9/21 4:00 PM

Chris Fraser, MSU

Braid group action on Grassmannian cluster varieties and spherical twists
 Chris Fraser, MSU
 Braid group action on Grassmannian cluster varieties and spherical twists
 09/21/2021
 4:00 PM  5:00 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Honghao Gao (gaohongh@msu.edu)
I will exhibit an action of the dstrand extended affine braid group on the topdimensional positroid variety in the Grassmannian Gr(k,n), where d = gcd(k,n). Roger Casals and Honghao Gao showed that this action can be used to exhibit infinitely many distinct Lagrangian fillings of (most) Legendrian torus knots. The braid group action is compatible with the cluster variety structure on Gr(k,n). Finally, I will discuss joint work in progress with Bernhard Keller which interprets this action as a composition of spherical twists in bounded derived categories which additively categorify the cluster algebra.

29123

Wednesday 9/22 3:00 PM

Einar Steingrímsson, University of Strathclyde

Permutation statistics and moment sequences
 Einar Steingrímsson, University of Strathclyde
 Permutation statistics and moment sequences
 09/22/2021
 3:00 PM  3:50 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Bruce E Sagan (bsagan@msu.edu)
Which combinatorial sequences correspond to moments of probability measures on the real line? We present a generating function, as a continued fraction, for a 14parameter family of integer sequences and interpret these in terms of statistics on permutations and other combinatorial objects. Special cases include several classical and noncommutative probability laws, and a substantial subset of the orthogonalizing measures in the qAskey scheme of orthogonal polynomials.
This continued fraction captures a variety of combinatorial sequences. In particular, it characterizes the moment sequences associated to the numbers of permutations avoiding (classical and vincular) patterns of length three. This connection between pattern avoidance and classical and noncommutative probability is among several consequences that generalize and unify previous results in the literature.
The fourteen combinatorial statistics further generalize to colored permutations, and, as an infinite family of statistics, to the karrangements: permutations with kcolored fixed points, introduced here. This is joint work with Natasha Blitvić, Lancaster University.

29122

Wednesday 9/22 4:00 PM

Ruoyu Wang , Northwestern

Boundary Stabilisation of Waves on Product Manifolds
 Ruoyu Wang , Northwestern
 Boundary Stabilisation of Waves on Product Manifolds
 09/22/2021
 4:00 PM  5:00 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Dapeng Zhan (zhan@msu.edu)
Take a square and consider the damped waves with boundary damping $a>0$ on the top side only. We will discuss my recent result implying that the energy of those waves must uniformly decay no faster than $t^{1/2}$, and no slower than it. We will also discuss this result in the context of product manifolds where the transverse geometric control is sufficient but not necessary for such energy decay.
Zoom passcode: A*****P**

29096

Thursday 9/23 2:30 PM

Joel Tropp, California Institute of Technology

Scalable semidefinite programming
 Joel Tropp, California Institute of Technology
 Scalable semidefinite programming
 09/23/2021
 2:30 PM  3:30 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Olga Turanova (turanova@msu.edu)
Semidefinite programming (SDP) is a powerful framework from convex optimization that has striking potential for data science applications. This talk describes a provably correct randomized algorithm for solving large, weakly constrained SDP problems by economizing on the storage and arithmetic costs. Numerical evidence shows that the method is effective for a range of applications, including relaxations of MaxCut, abstract phase retrieval, and quadratic assignment problems. Running on a laptop equivalent, the algorithm can handle SDP instances where the matrix variable has over 10^14 entries.
This talk will highlight the ideas behind the algorithm in a streamlined setting. The insights include a careful problem formulation, design of a bespoke optimization method, and use of randomized matrix computations.
Joint work with Alp Yurtsever, Olivier Fercoq, Madeleine Udell, and Volkan Cevher. Based on arXiv 1912.02949 (Scalable SDP, SIMODS 2021) and other papers (SketchyCGM in AISTATS 2017, Nyström sketch in NeurIPS 2017).

29129

Thursday 9/23 3:00 PM

Christopher Potvin, MSU

Hypergraphs & their Homology
 Christopher Potvin, MSU
 Hypergraphs & their Homology
 09/23/2021
 3:00 PM  4:00 PM
 C304 Wells Hall
 Danika Keala Van Niel (vannield@msu.edu)
Hypergraphs are generalizations of both graphs and simplicial complexes. They are often used to represent data for which graphs or simplices do not tell the whole story. As with many data structures, the new hotness is to do TDA (Topological Data Analysis) on hypergraphs. In this talk, I will introduce hypergraphs, why they are useful, and talk about their homology.
https://msu.zoom.us/j/91485321701
Meeting ID: 914 8532 1701
Passcode: SGTS

29130

Friday 9/24 3:00 PM

Jie Yang, MSU

An introduction to Fermat's Last Theorem
 Jie Yang, MSU
 An introduction to Fermat's Last Theorem
 09/24/2021
 3:00 PM  4:00 PM

(Virtual Meeting Link)
 Joshua Ruiter (ruiterj2@msu.edu)
In this talk, I will first introduce some motivations and historical works for FLT, then sketch modern ideas to attack this problem.

29139

Tuesday 9/28 11:10 AM

Brent Nelson, Michigan State University

Tomita–Takesaki theory for von Neumann algebras
 Brent Nelson, Michigan State University
 Tomita–Takesaki theory for von Neumann algebras
 09/28/2021
 11:10 AM  12:00 PM
 C304 Wells Hall
 Brent Nelson (banelson@msu.edu)
Tomita–Takesaki theory is a powerful (and often necessary) tool for studying von Neumann algebras that lack tracial states. It shows that any state on a von Neumann algebra $M$ automatically induces an action $\mathbb{R}\curvearrowright M$ (i.e. a noncommutative dynamical system) that then allows one to construct a crossed product von Neumann algebra $M\rtimes \mathbb{R}$. As the notation suggests, this crossed product is an analogue of semidirect products for groups, and it both contains $M$ and encodes the action via unitary elements. It turns out this crossed product always admits a trace (albeit an infinite one) and a dual action $\mathbb{R}\curvearrowright (M\rtimes \mathbb{R})$, and this structure was used by Alain Connes in 1973 to give a classification of the socalled type III von Neumann algebras. In this expository talk, I will provide an introduction to these ideas that does not require any previous experience with von Neumann algebras aside from some functional analysis (e.g. Hilbert spaces, bounded operators, and dual spaces).

29119

Tuesday 9/28 4:00 PM

Peng Zhou, Berkeley

Homological Mirror Symmetry for A_ntype cluster varieties
 Peng Zhou, Berkeley
 Homological Mirror Symmetry for A_ntype cluster varieties
 09/28/2021
 4:00 PM  5:00 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Honghao Gao (gaohongh@msu.edu)
The A_n type cluster variety, denoted by X_n, is the affine scheme associated to the upper cluster algebra of the A_n quiver (of n unfrozen vertices and one frozen vertex). The dual of X_n is denoted as Y_n, and is isomorphic but not canonically to X_n. For example, the variety X_1 is given by the equation {x y = 1 + q} where x, y are in \C and q is in \C^*. We prove that the homological mirror symmetry (HMS) conjecture for X_n, Y_n: the coherent sheaf category of Coh(X_n) is equivalent to the wrapped Fukaya category WFuk(Y_n), generalizing the known case for n=1 and 2. This is based on a recent work of GammageLe on HMS for truncated cluster variety, by putting back the 'truncated' part. This is work in progress, and is joint with Linhui Shen and Zhe Sun.

29097

Thursday 9/30 2:30 PM

Michael Perlmutter, UCLA

Neural Networks on (Directed) Graphs
 Michael Perlmutter, UCLA
 Neural Networks on (Directed) Graphs
 09/30/2021
 2:30 PM  3:30 PM
 Online (virtual meeting)
(Virtual Meeting Link)
The prevalence of graphbased data has spurred the rapid development of graph neural networks (GNNs) and related machine learning algorithms. These methods extend convolutions to graphs either in the spatial domain as a localized averaging operator or in the spectral domain via the eigendecomposition of a suitable Laplacian. However, most popular GNNs have two limitations. i) The filters used in these networks are essentially lowpass filters (i.e. averaging operators). This leads to the so called ``oversmoothing problem'' and the loss of highfrequency information. ii) If the graph is directed, as is the case in many applications including citation, website, and traffic networks, these networks are unable to effectively encode directional information. In this talk, discuss how we can overcome these limitations via i) the graph scattering transform, which uses bandpass filters rather than lowpass, and ii) MagNet, a network designed for directed graphs based on a complex Hermitian matrix known as the magnetic Laplacian.

29158

Thursday 9/30 3:00 PM

Keshav Sutrave, Michigan State University

Connections: a meditation in three parts
 Keshav Sutrave, Michigan State University
 Connections: a meditation in three parts
 09/30/2021
 3:00 PM  4:00 PM
 C304 Wells Hall
 Danika Keala Van Niel ()
No abstract available.

29140

Friday 10/1 3:00 PM

Peikai Qi, MSU

structure of finite generated Lambda module and its adjoint
 Peikai Qi, MSU
 structure of finite generated Lambda module and its adjoint
 10/01/2021
 3:00 PM  4:00 PM
 Online (virtual meeting)
 Chuangtian Guan ()
I will introduce the $\Lambda$module and talk about the structure and its adjoint in a classical language. If possible, I will talk about the generalized version of it and the reason that why we study it.

29105

Tuesday 10/5 4:00 PM

Daniel López Neumann, Indiana University

Twisting quantum invariants via Fox calculus
 Daniel López Neumann, Indiana University
 Twisting quantum invariants via Fox calculus
 10/05/2021
 4:00 PM  5:00 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Honghao Gao (gaohongh@msu.edu)
The ReshetikhinTuraev invariants of a knot are topological invariants built through the representation theory of certain Hopf algebras, such as quantum groups. In the early 2000s, Turaev introduced a Ggraded version of this construction that produces invariants of knots equipped with representations of their fundamental group into the group G.
This talk will be about a special case of the Ggraded construction. We will show that a graded Drinfeld double construction leads to ReshetikhinTuraev invariants of knots which are “twisted” via the usual Fox calculus. This construction applies to a wide class of Hopf algebras, and in the case of an exterior algebra, it specializes to the twisted Reidemeister torsion of the complement of a knot.

29137

Wednesday 10/6 3:00 PM

Richard A. Brualdi, University of Wisconsin  Madison

About Permutation Matrices
 Richard A. Brualdi, University of Wisconsin  Madison
 About Permutation Matrices
 10/06/2021
 3:00 PM  3:50 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Bruce E Sagan (bsagan@msu.edu)
The study of permutations is both ancient and modern. They can be viewed as the integers $1,2,\ldots,n$ in some order or as $n\times n$ permutation matrices. They can be regarded as data which is to be sorted. The explicit definition of the determinant uses permutations. An inversion of a permutation occurs when a larger integer precedes a smaller integer. Inversions can be used to define two partial orders on permutations, one weaker than the other. Partial orders have a unique minimal completion to a lattice, the DedekindMacNeille completion. Generalizations of permutation matrices determine related matrix classes, for instance, alternating sign matrices (ASMs) which arose independently in the mathematics and physics literature. Permutations may contain certain patterns, e.g. three integers in increasing order; avoiding such patterns determines certain permutation classes. Similar restrictions can be placed more generally on $(0,1)$matrices. The convex hull of $n\times n$ permutation matrices is the polytope of $n\times n$ doubly stochastic matrices. In a similar way we get ASM polytopes. We shall explore these and other ideas and their connections.

29138

Wednesday 10/6 4:00 PM

Shiva Chidambaram, MIT

Abelian varieties with given ptorsion representation
 Shiva Chidambaram, MIT
 Abelian varieties with given ptorsion representation
 10/06/2021
 4:00 PM  5:00 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Preston Wake (wakepres@msu.edu)
The Siegel modular variety $\mathcal{A}_2(3)$, which parametrizes abelian surfaces with full level $3$ structure, was recently shown to be rational over $\mathbf{Q}$ by Bruin and Nasserden. What can we say about its twist $\mathcal{A}_2(\rho)$ that parametrizes abelian surfaces $A$ whose $3$torsion representation is isomorphic to a given representation $\rho$? While it is not rational in general, it is always unirational over $\mathbf{Q}$ showing that $\rho$ arises as the $3$torsion representation of infinitely many abelian surfaces. We will discuss how we can obtain an explicit description of the universal object over such a unirational cover of $\mathcal{A}_2(\rho)$ using invariant theoretic ideas, thus parametrizing families of abelian surfaces with fixed $3$torsion representation. Similar ideas work in a few other cases, showing in particular that whenever $(g,p) = (1,2)$, $(1,3)$, $(1,5)$, $(2,2)$, $(2,3)$ and $(3,2)$, the necessary condition of cyclotomic similitude is also sufficient for a mod $p$ Galois representation to arise from the $p$torsion of a $g$dimensional abelian variety.

29132

Thursday 10/7 4:30 AM

Afonso Bandeira, ETHZ  Swiss Federal Institute of Technology Zürich

Noncommutative Matrix Concentration Inequalities
 Afonso Bandeira, ETHZ  Swiss Federal Institute of Technology Zürich
 Noncommutative Matrix Concentration Inequalities
 10/07/2021
 4:30 AM  5:30 AM
 Online (virtual meeting)
(Virtual Meeting Link)
 Olga Turanova (turanova@msu.edu)
Matrix Concentration inequalities such as Matrix Bernstein inequality have played an important role in many areas of pure and applied mathematics. These inequalities are intimately related to the celebrated noncommutative Khintchine inequality of LustPiquard and Pisier. In the middle of the 2010's, Tropp improved the dimensional dependence of this inequality in certain settings by leveraging cancellations due to noncommutativity of the underlying random matrices, giving rise to the question of whether such dependency could be removed.
In this talk we leverage ideas from Free Probability to fully remove the dimensional dependence in a range of instances, yielding optimal bounds in many settings of interest. As a byproduct we develop matrix concentration inequalities that capture noncommutativity (or, to be more precise, ``freeness''), improving over Matrix Bernstein in a range of instances. No background knowledge of Free Probability will be assumed in the talk.
Joint work with March Boedihardjo and Ramon van Handel, more information at arXiv:2108.06312 [math.PR].

29157

Thursday 10/7 3:00 PM

Chris St. Clair, Michigan State University

Knots and Crosses: An Introduction to Grid Diagrams
 Chris St. Clair, Michigan State University
 Knots and Crosses: An Introduction to Grid Diagrams
 10/07/2021
 3:00 PM  4:00 PM
 C304 Wells Hall
 Danika Keala Van Niel (vannield@msu.edu)
Grid diagrams are a type of knot diagram which allow us to tackle problems in knot theory combinatorially. After introducing them we will explore some examples of their use in traditional knot invariants and hint at their place in understanding manifolds.

29145

Thursday 10/7 4:00 PM

David Penneys, The Ohio State University

Fusion categories in mathematics and physics
 David Penneys, The Ohio State University
 Fusion categories in mathematics and physics
 10/07/2021
 4:00 PM  5:00 PM
 C304 Wells Hall
(Virtual Meeting Link)
 Brent Nelson (banelson@msu.edu)
Classically, the notion of symmetry is described by a group. In recent decades, we have seen the emergence of quantum mathematical objects whose symmetries are best described by tensor categories. Fusion categories simultaneously generalize the notion of a finite group and its category of finite dimensional complex representations, and we think of these objects as encoding quantum symmetries. We will give a basic introduction to the theory of fusion categories and describe applications to some areas of mathematics and physics, namely operator algebras and theoretical condensed matter. [Zoom passcode distributed upon request.]

29151

Tuesday 10/12 10:00 AM

Zheng Xiao, MSU

CMalgebra and CMtypes
 Zheng Xiao, MSU
 CMalgebra and CMtypes
 10/12/2021
 10:00 AM  11:00 AM
 Online (virtual meeting)
(Virtual Meeting Link)
 Zheng Xiao (xiaozhen@msu.edu)
No abstract available.

29153

Tuesday 10/12 11:10 AM

Matthew Lorentz, Michigan State University

Derivations and the Hochschild Cohomology of Uniform Roe Algebras, Part 3
 Matthew Lorentz, Michigan State University
 Derivations and the Hochschild Cohomology of Uniform Roe Algebras, Part 3
 10/12/2021
 11:10 AM  12:00 PM
 C304 Wells Hall
 Brent Nelson (banelson@msu.edu)
In this series of talks we show a necessary and sufficient condition for the vanishing of the Hochschild cohomology of a uniform Roe algebra. Specifically, the ndimensional continuous Hochschild cohomology vanishes if and only if every norm continuous nlinear map from the uniform Roe algebra to itself is equivalent to a weakly continuous nlinear map.
Hochschild cohomology was introduced by Gerhard Hochschild in his 1945 paper “On the Cohomology Groups of an Associative Algebra”. The Hochschild cohomology of associative algebras has become a useful object of study in many fields of mathematics such as representation theory, mathematical physics, and noncommutative geometry, to name a few.
Last time we showed that all bounded derivations on uniform Roe algebras are inner. The first Hochschild cohomology measures how close derivations are to being inner. Hence, our result from last time can be restated as the first Hochschild cohomology of the uniform Roe algebra vanishing. It is then natural to ask if the higher dimensional cohomologies also vanish.
We will begin with the definition and several properties of multilinear maps which are essential to building the Hochschild complex. We then define the Hochschild complex and Hochschild cohomology as they apply to multilinear maps from a C*algebra A to a Banach Abimodule V. We then review many properties of these cohomologies. Lastly, we will show that if all nlinear maps have a weakly continuous representation in the Hochschild cohomology then the n’th dimensional Hochschild cohomology vanishes.

29113

Tuesday 10/12 4:00 PM

Ka Ho Wong, Texas A&M University

Asymptotics of the relative ReshetikhinTuraev invariants
 Ka Ho Wong, Texas A&M University
 Asymptotics of the relative ReshetikhinTuraev invariants
 10/12/2021
 4:00 PM  5:00 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Honghao Gao (gaohongh@msu.edu)
In a series of joint works with Tian Yang, we made a volume conjecture and an asymptotic expansion conjecture for the relative ReshetikhinTuraev invariants for a closed oriented 3manifold with a colored framed link inside it. We propose that their asymptotic behavior is related to the volume, the ChernSimons invariant and the adjoint twisted Reidemeister torsion associated with the hyperbolic cone metric on the manifold with singular locus the link and cone angles determined by the coloring.
In this talk, I will first discuss how our volume conjecture can be understood as an interpolation between the KashaevMurakamiMurakami volume conjecture of the colored Jones polynomials and the ChenYang volume conjecture of the ReshetikhinTuraev invariants. Then I will describe how the adjoint twisted Reidemeister torsion shows up in the asymptotic expansion of the invariants. Especially, we find new explicit formulas for the adjoint twisted Reidemeister torsion for the fundamental shadow link complements and for the 3manifold obtained by doing hyperbolic Dehnfilling on those link complements. Those formulas cover a very large class of hyperbolic 3manifold and appear naturally in the asymptotic expansion of quantum invariants. Finally, I will summarize the recent progress of the asymptotic expansion conjecture of the fundamental shadow link pairs.

29150

Wednesday 10/13 3:00 PM

Greta Panova, USC

Hook length formulas for skew shapes and beyond
 Greta Panova, USC
 Hook length formulas for skew shapes and beyond
 10/13/2021
 3:00 PM  3:50 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Bruce E Sagan (bsagan@msu.edu)
Abstract: The hook length formula for the number of Standard Young Tableaux of a partition lambda is one of the few miraculous product formulas we see in combinatorics. While no such formula for the number of skew SYTs exists in general, the recent Naruse Hook Length Formula (NHLF) brings us close. I will explain this formula and generalizations, give some proofs and bijections, and discuss new extensions of NHLF for increasing tableaux originating in the study of Grothendieck polynomials.
Based on a series of papers with A. Morales and I. Pak

29147

Wednesday 10/13 4:00 PM

Honghao Gao, MSU

Rigidity in contact topology
 Honghao Gao, MSU
 Rigidity in contact topology
 10/13/2021
 4:00 PM  5:00 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Preston Wake (wakepres@msu.edu)
Legendrian links play a central role in low dimensional contact topology. A rigid theory uses invariants constructed via algebraic tools to distinguish Legendrian links. The most influential and powerful invariant is the ChekanovEliashberg differential graded algebra (Chekanov, Inventiones, 2002), which set apart the first nonclassical Legendrian pair and stimulated many subsequent developments. The functor of points for the dga is a moduli space which acquires rich algebraic structures and can distinguish exact Lagrangian fillings. Such fillings are difficult to construct and to study, whereas the only known classification is the unique filling for Legendrian unknot (EliashbergPolterovich, Annals, 1996). For a long time, a folklore belief is that exact Lagrangian fillings are scarce and a Legendrian link can only have finitely many, based on the observation from limited examples.
In this talk, I will report a joint work with Roger Casals, where we applied the techniques from contact topology, microlocal sheaf theory and cluster algebras, and successfully found the first examples of Legendrian links with infinitely many Lagrangian fillings, reversing the general belief.

29133

Thursday 10/14 2:30 PM

Edgar Dobriban, University of Pennsylvania

Asymptotic perspectives on sketching
 Edgar Dobriban, University of Pennsylvania
 Asymptotic perspectives on sketching
 10/14/2021
 2:30 PM  3:30 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Olga Turanova (turanova@msu.edu)
Sketching and random projection methods are a powerful set of techniques to speed up computations in numerical linear algebra, statistics, machine learning, optimization and data science. In this talk, we will discuss some of our works on developing a "big data" asymptotic perspective on sketching in the fundamental problems of linear regression and principal component analysis. This can lead to remarkably clean and elegant mathematical results, which yield powerful insights into the performance of various sketching methods. To highlight one, orthogonal sketches such as the Subsampled Randomized Hadamard Transform are provably better than iid sketches such as Gaussian sketching. This is obtained by using deep recent tools from asymptotic random matrix theory and free probability, including asymptotically liberating sequences (Anderson & Farrell, 2014). This is based on joint works with Jonathan Lacotte, Sifan Liu, Mert Pilanci, David P. Woodruff, and Fan Yang.

29152

Thursday 10/14 3:00 PM

Joseph Melby, Michigan State University

Quantum invariants, shadows, and volume
 Joseph Melby, Michigan State University
 Quantum invariants, shadows, and volume
 10/14/2021
 3:00 PM  4:00 PM
 C304 Wells Hall
 Danika Keala Van Niel (vannield@msu.edu)
I will give some sort of introduction to a cool quantum 3manifold invariant called the TuraevViro invariant and connect it to hyperbolic geometry through the Volume Conjecture. Then we will talk about shadows of 4manifolds and how they can be used to prove the asymptotic additivity (we made this term up) of the TuraevViro invariants for a certain family of link complements.

29149

Thursday 10/14 4:00 PM

Semyon Dyatlov, Massachusetts Institute of Technology

What is quantum chaos?
 Semyon Dyatlov, Massachusetts Institute of Technology
 What is quantum chaos?
 10/14/2021
 4:00 PM  5:00 PM
 C304 Wells Hall
(Virtual Meeting Link)
 Brent Nelson (banelson@msu.edu)
Where do eigenfunctions of the Laplacian concentrate as eigenvalues go to infinity? Do they equidistribute or do they concentrate in an uneven way? It turns out that the answer depends on the nature of the geodesic flow. I will discuss various results in the case when the flow is chaotic: the Quantum Ergodicity theorem of Shnirelman, Colin de Verdière, and Zelditch, the Quantum Unique Ergodicity conjecture of Rudnick–Sarnak, the progress on it by Lindenstrauss and Soundararajan, and the entropy bounds of Anantharaman–Nonnenmacher. I will conclude with a more recent lower bound on the mass of eigenfunctions obtained with Jin and Nonnenmacher. It relies on a new tool called "fractal uncertainty principle" developed in the works with Bourgain and Zahl.

29154

Tuesday 10/19 10:00 AM

Yingda Cheng, Michigan State University

AMS/AWM Joint Lecture: Computational Methods for Kinetic Transport Equations
 Yingda Cheng, Michigan State University
 AMS/AWM Joint Lecture: Computational Methods for Kinetic Transport Equations
 10/19/2021
 10:00 AM  11:00 AM
 Online (virtual meeting)
(Virtual Meeting Link)
 Nicole Hayes (hayesni4@msu.edu)
Kinetic equations are mesoscale description of the
transport of particles such as neutrons, photons, electrons,
molecules as well as their interaction with a background
medium or among themselves, and they have wide applications in many areas of mathematical physics, such as nuclear engineering, fusion device, optical tomography, rarefied gas dynamics, semiconductor device design, traffic network, swarming, etc. Because the equations are posed in the phase space (physical space plus velocity space), any gridbased method will run into computational bottleneck in real applications that are 3D in physical space and 3D in velocity space.
This talk will survey three numerical solvers that we developed aiming at efficient computations of kinetic equations: the adaptive sparse grid discontinuous Galerkin method, the reduced basis method and the machine learning moment closure method. They aim at effective reduced order computations of such high dimensional equations. Benchmark numerical examples will be presented.
Finally, I will introduce WINASc: Women in Numerical Analysis and Scientific Computing, which is part of the AWM advance network.
Meeting Zoom password: awmams

29170

Tuesday 10/19 10:00 AM

Zheng Xiao, MSU

CMalgebra and CMtypes, II
 Zheng Xiao, MSU
 CMalgebra and CMtypes, II
 10/19/2021
 10:00 AM  11:00 AM
 C304 Wells Hall
 Zheng Xiao (xiaozhen@msu.edu)
No abstract available.

29112

Tuesday 10/19 3:00 PM

Francis Bonahon, USC

Quantum invariants of surface diffeomorphisms and 3dimensional hyperbolic geometry
 Francis Bonahon, USC
 Quantum invariants of surface diffeomorphisms and 3dimensional hyperbolic geometry
 10/19/2021
 3:00 PM  4:00 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Honghao Gao (gaohongh@msu.edu)
This talk is motivated by surprising connections between two very different approaches to 3dimensional topology, namely quantum topology and hyperbolic geometry. The KashaevMurakamiMurakami Volume Conjecture connects the growth of colored Jones polynomials of a knot to the hyperbolic volume of its complement. More precisely, for each integer n, one evaluates the nth Jones polynomial of the knot at the nroot of unity exp(2 pi i/n). The Volume Conjecture predicts that this sequence grows exponentially as n tends to infinity, with exponential growth rate related to the hyperbolic volume of the knot complement.
I will discuss a closely related conjecture for diffeomorphisms of surfaces, based on the representation theory of the Kauffman bracket skein algebra of the surface, a quantum topology object closely related to the Jones polynomial of a knot. I will describe the mathematics underlying this conjecture, which involves a certain Frobenius principle in quantum algebra. I will also present experimental evidence for the conjecture, and describe partial results obtained in work in progress with Helen Wong and Tian Yang.

29155

Wednesday 10/20 3:00 PM

Jessica Striker, North Dakota State University

Promotion, rotation, and a web basis of invariant polynomials from noncrossing partitions
 Jessica Striker, North Dakota State University
 Promotion, rotation, and a web basis of invariant polynomials from noncrossing partitions
 10/20/2021
 3:00 PM  3:50 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Bruce E Sagan (bsagan@msu.edu)
Many combinatorial objects with strikingly good enumerative formulae and dynamical behavior (such as cyclic sieving) have underlying algebraic meaning. We first review classical results on promotion of standard Young tableaux, rotation of matchings/webs, and related invariant polynomials and symmetric group actions. We then discuss recent joint work with Rebecca Patrias and Oliver Pechenik involving the more general setting of increasing tableaux and noncrossing partitions.

29148

Wednesday 10/20 4:00 PM

Yizheng Yuan, TU Berlin

Refined regularity of SLE
 Yizheng Yuan, TU Berlin
 Refined regularity of SLE
 10/20/2021
 4:00 PM  5:00 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Dapeng Zhan (zhan@msu.edu)
SLE (SchrammLoewner evolution) is a family of random planar curves that have some natural conformal invariance properties. They appear in a variety of planar models that exhibit conformal invariance in the scaling limit. In this talk I will introduce SLE and describe its regularity. Regarding the regularity, the optimal Hoelder and pvariation exponents are known from previous works. I will present a new approach that refines the results to the logarithmic scale.
Zoom Passcode: A*****P**

29126

Wednesday 10/20 4:00 PM

Olivier Martin, Stony Brook University

Rational maps from products of curves
 Olivier Martin, Stony Brook University
 Rational maps from products of curves
 10/20/2021
 4:00 PM  5:00 PM
 Online (virtual meeting)
 Francois Greer (greerfra@msu.edu)
I will present recent joint work with N. Chen about dominant rational maps from products of curves to surfaces with p_g=q=0. The gonality of an algebraic curve C is the minimal degree of a nonconstant morphism from C to the projective line. Our main result is that under some assumptions the minimal degree of a dominant rational map from a product of two curves to a surface with p_g=q=0 is the product of their gonalities. In particular, a product of hyperelliptic curves of general type does not admit dominant rational maps of degree less than 4 to P^2. I will finish by presenting open problems and some strategies to attack them.

29134

Thursday 10/21 4:30 AM

Bubacarr Bah, African Institute for Mathematical Sciences South Africa

Cancelled
 Bubacarr Bah, African Institute for Mathematical Sciences South Africa
 Cancelled
 10/21/2021
 4:30 AM  5:30 AM
 Online (virtual meeting)
(Virtual Meeting Link)
 Olga Turanova (turanova@msu.edu)
Cancelled

29160

Thursday 10/21 3:00 PM

Tristan Wells, Michigan State University

Introduction to Trisections of 4 Manifolds
 Tristan Wells, Michigan State University
 Introduction to Trisections of 4 Manifolds
 10/21/2021
 3:00 PM  4:00 PM
 C304 Wells Hall
 Danika Keala Van Niel ()
This talk aims to introduce and give an overview of a tool for studying four manifolds which I explored in some depth at a recent workshop at the University of Nebraska this summer: Trisections. Pioneered by Rob Kirby and David Gay, the slogan "trisections are to 4manifolds as Heegaard splittings are to 3manifolds" encouraged many other lowdimensional topologists to investigate this tool further. In particular, I'll define a 4manifold trisections, present some of their basic properties, some nice results from trisection literature, and some of the numerous problems and questions going forward.

29146

Thursday 10/21 4:00 PM

Jared Bronski, University of Illinois at Urbana–Champaign

Index Results for the Kuramoto model
 Jared Bronski, University of Illinois at Urbana–Champaign
 Index Results for the Kuramoto model
 10/21/2021
 4:00 PM  5:00 PM
 C304 Wells Hall
(Virtual Meeting Link)
 Brent Nelson (banelson@msu.edu)
The Kuramoto model is a system of ordinary differential equations modeling the nonlinear interactions of a group phase oscillators. The Kuramoto and related models have been proposed as models for phenomenon like the synchronized flashing of fireflies and the dynamics of circadian rhythms and jet lag. We consider a number of problems in the stability of synchronized solutions to this model. Many of these problems involve some sort of index result, counting the dimension of some unstable manifold. We employ a number of different techniques including geometric, topological, and graphtheoretic ideas. [Zoom passcode distributed upon request.]

29171

Tuesday 10/26 10:00 AM

Peikai Qi, MSU

The reflex field of CMpairs
 Peikai Qi, MSU
 The reflex field of CMpairs
 10/26/2021
 10:00 AM  11:00 AM
 C304 Wells Hall
(Virtual Meeting Link)
 Zheng Xiao (xiaozhen@msu.edu)
No abstract available.

29108

Tuesday 10/26 4:00 PM

Break day, no talk

TBA
 Break day, no talk
 TBA
 10/26/2021
 4:00 PM  5:00 PM
 Online (virtual meeting)
 Honghao Gao (gaohongh@msu.edu)
TBA

29172

Wednesday 10/27 3:00 PM

Quinn Minnich, Michigan State University

Counting Admissible Orderings of a Pinnacle Set
 Quinn Minnich, Michigan State University
 Counting Admissible Orderings of a Pinnacle Set
 10/27/2021
 3:00 PM  3:50 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Bruce E Sagan (bsagan@msu.edu)
Let $S_n$ be the symmetric group. The pinnacle set of a permutation in $S_n$ is defined to be all elements of that permutation which are larger than both of their adjacent elements. Given a subset $P$ of $\{1,\ldots,n\}$ we can also ask if there exists a permutation in $S_n$ having $P$ as its pinnacle set. If so, we say $P$ is admissible. We can extend this idea further by ordering the elements of $P$ and asking if there exists a permutation in $S_n$ having pinnacle set $P$ with the elements of $P$ in the given order. If so, we say that the ordering is an admissible ordering. In this presentation, we will present an efficient recursion for counting the number of admissible orderings of a given pinnacle set.

29127

Wednesday 10/27 4:00 PM

Eoin Mackall, University of Maryland

Chow groups of SeveriBrauer varieties and biquaternion algebras
 Eoin Mackall, University of Maryland
 Chow groups of SeveriBrauer varieties and biquaternion algebras
 10/27/2021
 4:00 PM  5:00 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Igor Rapinchuk (rapinchu@msu.edu)
The Chow groups of SeveriBrauer varieties associated to biquaternion division algebras were originally computed by Karpenko in the mid nineties. The main difficulty in these computations is determining whether or not CH^2, the group of codimension 2 cycles, contains nontrivial torsion; for these varieties this group is torsionfree. Since his original proof, Karpenko has given two other proofs of this result. All of these proofs involve some clever use of Ktheory to determine relations between some explicit cycles. In this talk, I'll discuss a new geometric method that one can use to determine these same relations. Passcode: MSUALG

29135

Thursday 10/28 2:30 PM

Rongrong Wang, Michigan State University

Sigma Delta quantization on images, manifolds, and graphs
 Rongrong Wang, Michigan State University
 Sigma Delta quantization on images, manifolds, and graphs
 10/28/2021
 2:30 PM  3:30 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Olga Turanova (turanova@msu.edu)
In digital signal processing, quantization is the step of converting a signal's realvalued samples into a finite string of bits. As the first step in digital processing, it plays a crucial role in determining the information conversion rate and the reconstruction accuracy. Compared to nonadaptive quantizers, the adaptive ones are known to be more efficient in quantizing bandlimited signals, especially when the bitbudget is small (e.g.,1 bit) and noises are present.
However, adaptive quantizers are currently only designed for 1D functions/signals. In this talk, I will discuss challenges in extending it to high dimensions and present our proposed solutions. Specifically, we design new adaptive quantization schemes to quantize images/videos as well as functions defined on 2D surface manifolds and general graphs, which are common objects in signal processing and machine learning. Mathematically, we start from the 1D SigmaDelta quantization, extend them to highdimensions and build suitable decoders. The discussed theory would be useful in natural image acquisition, medical imaging, 3D printing, and graph embedding.

29161

Thursday 10/28 3:00 PM

Jared Able, Michigan State University

Murasugi sums and braids
 Jared Able, Michigan State University
 Murasugi sums and braids
 10/28/2021
 3:00 PM  4:00 PM
 C304 Wells Hall
 Danika Keala Van Niel ()
For your favorite knot K, there's a braid diagram for K with n strings, and there are (n2) ways to split the braid along a string into a pair of braids. What pairs of braids can this splitting yield? To answer this question, we take a detour into the realm of the Murasugi sum, an operation on knots and their Seifert surfaces.

29141

Thursday 10/28 4:00 PM

Andrei Caldararu, University of Wisconsin

Yet another Moonshine
 Andrei Caldararu, University of Wisconsin
 Yet another Moonshine
 10/28/2021
 4:00 PM  5:00 PM
 C304 Wells Hall
 Francois Greer (greerfra@msu.edu)
The jfunction, introduced by Felix Klein in 1879, is an essential ingredient in the study of elliptic curves. It is Zperiodic on the complex upper halfplane, so it admits a Fourier expansion. The original Monstrous Moonshine conjecture, due to McKay and Conway/Norton in the 1980s, relates the Fourier coefficients of the jfunction around the cusp to dimensions of irreducible representations of the Monster simple group. It was proved by Borcherds in 1992.
In my talk I will try to give a rudimentary introduction to modular forms, explain Monstrous Moonshine, and discuss a new version of it obtained in joint work with Yunfan He and Shengyuan Huang. Our version involves studying the jfunction around CM points (socalled LandauGinzburg points in the physics literature) and expanding with respect to a coordinate which arises naturally in string theory.

29156

Friday 10/29 3:00 PM

Mike Annunziata, Chuangtian Guan, Nick Rekuski, and Joshua Ruiter, MSU

Lightning talks
 Mike Annunziata, Chuangtian Guan, Nick Rekuski, and Joshua Ruiter, MSU
 Lightning talks
 10/29/2021
 3:00 PM  4:00 PM

(Virtual Meeting Link)
 Joshua Ruiter (ruiterj2@msu.edu)
Each of the four speakers will give a brief (1012 minute) introduction to their research.

29106

Tuesday 11/2 4:00 PM

James Hughes, UC Davis

TBA

29125

Wednesday 11/3 4:00 PM

Xin Sun, University of Pennsylvania

Two types of integrability in Liouville quantum gravity
 Xin Sun, University of Pennsylvania
 Two types of integrability in Liouville quantum gravity
 11/03/2021
 4:00 PM  5:00 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Dapeng Zhan (zhan@msu.edu)
There are two major resources of integrability in Liouville quantum gravity: conformal field theory and random planar maps decorated with statistical physics models. I will give a few examples of each type and explain how these two types are compatible. Recently, cutting and gluing random surfaces in LQG using SLE curves allows us to blend these two types of integrability to obtain exact results on Liouville conformal field theory, mating of trees, SchrammLoewner evolution, and conformal loop ensemble. I will present a few results in this direction. Based on joint works with Morris Ang, Nina Holden and Guillaume Remy.
Zoom passcode: A*****P**

29143

Wednesday 11/3 4:00 PM

Karl Schwede, University of Utah

TBA
 Karl Schwede, University of Utah
 TBA
 11/03/2021
 4:00 PM  5:00 PM
 C304 Wells Hall
 Rankeya Datta (dattaran@msu.edu)
No abstract available.

29136

Thursday 11/4 2:30 PM

Weilin Li, New York University

TBA
 Weilin Li, New York University
 TBA
 11/04/2021
 2:30 PM  3:30 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Olga Turanova (turanova@msu.edu)
TBA

29162

Thursday 11/4 3:00 PM

Zhixin Wang, Michigan State University

TBD
 Zhixin Wang, Michigan State University
 TBD
 11/04/2021
 3:00 PM  4:00 PM
 C304 Wells Hall
 Danika Keala Van Niel ()
No abstract available.

29111

Tuesday 11/9 4:00 PM

Mike Wong, Dartmouth

TBA

29128

Wednesday 11/10 4:00 PM

Rong Zhou, Cambridge

TBA
 Rong Zhou, Cambridge
 TBA
 11/10/2021
 4:00 PM  5:00 PM
 Online (virtual meeting)
 Preston Wake (wakepres@msu.edu)
No abstract available.

29167

Thursday 11/11 4:30 AM

Sjoerd Dirksen, Utrecht University

TBA
 Sjoerd Dirksen, Utrecht University
 TBA
 11/11/2021
 4:30 AM  5:30 AM
 Online (virtual meeting)
(Virtual Meeting Link)
 Olga Turanova (turanova@msu.edu)
TBA

29163

Thursday 11/11 3:00 PM

Astrid Olave, Michigan State University

Revealing brain network dynamics during the emotional state of suspense using topological data analysis
 Astrid Olave, Michigan State University
 Revealing brain network dynamics during the emotional state of suspense using topological data analysis
 11/11/2021
 3:00 PM  4:00 PM
 C304 Wells Hall
 Danika Keala Van Niel ()
No abstract available.

29144

Thursday 11/11 4:00 PM

Kevin Buzzard, Imperial College London

TBA
 Kevin Buzzard, Imperial College London
 TBA
 11/11/2021
 4:00 PM  5:00 PM
 Online (virtual meeting)
 Francois Greer (greerfra@msu.edu)
No abstract available.

29117

Tuesday 11/16 4:00 PM

Anastasiia Tsvietkova, Rutgers

TBA
 Anastasiia Tsvietkova, Rutgers
 TBA
 11/16/2021
 4:00 PM  5:00 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Honghao Gao (gaohongh@msu.edu)
TBA

29121

Wednesday 11/17 4:00 PM

Katrina Honigs, Simon Fraser University

TBA
 Katrina Honigs, Simon Fraser University
 TBA
 11/17/2021
 4:00 PM  5:00 PM
 Online (virtual meeting)
 Igor Rapinchuk (rapinchu@msu.edu)
No abstract available.

29168

Thursday 11/18 4:30 AM

Lorenzo Rosasco, MIT/University of Genova

TBA
 Lorenzo Rosasco, MIT/University of Genova
 TBA
 11/18/2021
 4:30 AM  5:30 AM
 Online (virtual meeting)
(Virtual Meeting Link)
 Olga Turanova (turanova@msu.edu)
TBA

29164

Thursday 11/18 3:00 PM

TBD, Michigan State University

TBD
 TBD, Michigan State University
 TBD
 11/18/2021
 3:00 PM  4:00 PM
 C304 Wells Hall
 Danika Keala Van Niel ()
No abstract available.

29142

Thursday 11/18 4:00 PM

Anna Seigal, University of Oxford

TBA
 Anna Seigal, University of Oxford
 TBA
 11/18/2021
 4:00 PM  5:00 PM
 Online (virtual meeting)
 Francois Greer (greerfra@msu.edu)
No abstract available.

29124

Tuesday 11/23 4:00 PM

Vijay Higgins, MSU

TBA

29169

Thursday 11/25 4:30 AM

Alexandra Carpentier, Otto von Guericke Universität Magdeburg

TBA
 Alexandra Carpentier, Otto von Guericke Universität Magdeburg
 TBA
 11/25/2021
 4:30 AM  5:30 AM
 Online (virtual meeting)
(Virtual Meeting Link)
 Olga Turanova (turanova@msu.edu)
TBA

29109

Wednesday 12/1 4:00 PM

Jack Petok, Dartmouth

TBA
 Jack Petok, Dartmouth
 TBA
 12/01/2021
 4:00 PM  5:00 PM
 Online (virtual meeting)
 Laure Flapan (flapanla@msu.edu)
TBA

29165

Thursday 12/2 3:00 PM

Danika Van Niel, Michigan State University

Isotropy Separation Sequence Part 1
 Danika Van Niel, Michigan State University
 Isotropy Separation Sequence Part 1
 12/02/2021
 3:00 PM  4:00 PM
 C304 Wells Hall
 Danika Keala Van Niel ()
No abstract available.

29173

Tuesday 12/7 11:00 AM

Umut Varolgunes, Edinburgh Hodge Institute

TBA
 Umut Varolgunes, Edinburgh Hodge Institute
 TBA
 12/07/2021
 11:00 AM  11:50 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Honghao Gao (gaohongh@msu.edu)
TBA

29116

Wednesday 12/8 4:00 PM

Salim Tayou, Harvard University

TBA
 Salim Tayou, Harvard University
 TBA
 12/08/2021
 4:00 PM  5:00 PM
 C304 Wells Hall
 Francois Greer (greerfra@msu.edu)
No abstract available.

29166

Thursday 12/9 3:00 PM

Chloe Lewis, Michigan State University

Isotropy Separation Sequence Part 2
 Chloe Lewis, Michigan State University
 Isotropy Separation Sequence Part 2
 12/09/2021
 3:00 PM  4:00 PM
 C304 Wells Hall
 Danika Keala Van Niel ()
No abstract available.

29115

Tuesday 12/14 4:00 PM

YuShen Lin, Boston University

TBA
 YuShen Lin, Boston University
 TBA
 12/14/2021
 4:00 PM  5:00 PM
 Online (virtual meeting)
(Virtual Meeting Link)
 Honghao Gao (gaohongh@msu.edu)
TBA
