Seminars and Colloquia by Series

The HRT Conjecture for a Symmetric (3,2) Configuration

Series
Analysis Seminar
Time
Wednesday, January 28, 2026 - 14:00 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Shuang GuanTufts University

The Heil-Ramanathan-Topiwala (HRT) conjecture is an open problem in time-frequency analysis. It asserts that any finite combination of time-frequency shifts of a non-zero function in $L^2(\mathbb{R})$ is linearly independent. Despite its simplicity, the conjecture remains unproven in full generality, with only specific cases resolved.
In this talk, I will discuss the HRT conjecture for a specific symmetric configuration of five points in the time-frequency plane, known as the $(3,2)$ configuration. Building upon restriction principles, we prove that for this specific setting, the Gabor system is linearly independent whenever the parameters satisfy certain rationality conditions (specifically, when one parameter is irrational and the other is rational). This result partially resolves the remaining open cases for such configurations. I will outline the proof methods, which involve an interplay of harmonic analysis and ergodic theory. This is joint work with Kasso A. Okoudjou.

Entrywise positivity preservers and sign preservers

Series
Algebra Seminar
Time
Monday, January 26, 2026 - 13:00 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Chi Hoi (Kyle) YipGeorgia Institute of Technology

Please Note: The talk will be held in a hybrid format. ( https://gatech.zoom.us/j/95766668962?pwd=uXNAdqzq8IpL1T2bQONQhUg77iCQyP.1 / Meeting ID: 957 6666 8962 / PW: 232065 )

Let $A = (a_{ij})$ be an $n \times n$ matrix with entries in a field $\mathbb{F}$ and let $f$ be a function defined on $\mathbb{F}$. The function naturally induces an entrywise transformation of $A$ via $f[A] := (f(a_{ij}))$. The study of such entrywise transforms that preserve various forms of matrix positivity has a rich and long history since the seminal work of Schoenberg. In this talk, I will discuss recent developments in the setting that the underlying field $\mathbb{F}$ is the real field, the complex field, and finite fields. I will also highlight some interesting connections between these problems with arithmetic combinatorics, finite geometry, and graph theory. Joint work with Dominique Guillot, Himanshu Gupta, and Prateek Kumar Vishwakarma.

Improving $R(3,k)$ in just two bites

Series
Combinatorics Seminar
Time
Friday, January 23, 2026 - 15:15 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Florian PfenderUniversity of Colorado Denver

We present a random construction proving that the extreme off-diagonal Ramsey numbers satisfy $R(3,k)\ge  \left(\frac12+o(1)\right)\frac{k^2}{\log{k}}$ (conjectured to be asymptotically tight), improving the previously best bound $R(3,k)\ge  \left(\frac13+o(1)\right)\frac{k^2}{\log{k}}$. In contrast to all previous constructions achieving the correct order of magnitude, we do not use a nibble argument.

Beyond the paper, we will explore a bit further how the approach can be used for other problems.

A Lovász-Kneser theorem for triangulations

Series
Additional Talks and Lectures
Time
Friday, January 23, 2026 - 11:00 for 1 hour (actually 50 minutes)
Location
Skiles 249
Speaker
Michael ZhengEmory University

In a highly influential paper from 1978, Lovász used topological methods to determine the chromatic number of the Kneser graph of the set of k-element subsets of a set with n elements. In this talk, we will discuss the Kneser graph of the set of triangulations of a convex n-gon and a recent proof that the chromatic number of this graph is n-2. The geometry of the associahedron will play a particularly important role in the argument. Based on a joint work with Anton Molnar, Cosmin Pohoata and Daniel Zhu.

Universality limits for orthogonal polynomials

Series
Math Physics Seminar
Time
Friday, January 23, 2026 - 11:00 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Milivoje LukicEmory University

The local spacing of zeros of orthogonal polynomials is studied using scaling limits of Christoffel--Darboux kernels. Different limit kernels are associated with different universality classes, e.g. sine kernel with bulk universality and locally asymptotically uniform zero spacing. In recent years, new results have been obtained by using the de Branges theory of canonical systems. This includes necessary and sufficient conditions for a family of scaling limits corresponding to homogeneous de Branges spaces; this family includes bulk universality, hard edge universality, jump discontinuities in the weight, and other notable universality classes. It also includes local behaviors beyond scaling limits. The talk is based on joint works with Benjamin Eichinger, Brian Simanek, Harald Woracek, Peter Yuditskii.

The Uzawa Method: Historical Perspectives, Current Advances, and Future Directions

Series
Applied and Computational Mathematics Seminar
Time
Friday, January 23, 2026 - 11:00 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Professor Xiaoming YuanThe University of Hong Kong

Abstract:
This talk explores the Uzawa method, tracing its development from early applications in partial differential equations (PDEs) to modern advancements in optimization, image processing, and scientific computing. We will examine recent refinements for developing GPU-adaptive solvers for huge-scale linear programming and its extension to semidefinite programming arising in quantum information science. The discussion will also highlight the method's integration with deep learning and unrolling techniques for optimal control problems of PDEs, as well as its applications in industry.

 

Bio:

Xiaoming Yuan is a Professor in the Department of Mathematics at The University of Hong Kong. His research spans optimization, optimal control, scientific machine computing, and artificial intelligence. He is well recognized for his fundamental contributions to first-order optimization algorithms, including the Alternating Direction Method of Multipliers (ADMM), primal-dual methods, and proximal point algorithms. He also collaborates extensively with the AI and cloud computing industries. He led the development of the first automatic bandwidth allocation system for the cloud computing sector. His team was honored as a Franz Edelman Award Finalist in 2023.

Similarities and Differences between the Longest Common and Longest Common and Increasing Subsequences in Random Words

Series
Stochastics Seminar
Time
Thursday, January 22, 2026 - 15:30 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Christian HoudréGeorgia Institute of Technology

Let $LC_n$ be the length of the longest common subsequences of two independent random words whose letters are taken  in a finite alphabet and when the alphabet is totally ordered and let $LCI_n$ be the length of the longest common and increasing subsequences of the words.   Results on the asymptotic means, variances and limiting laws of these well-known random objects will be described and compared.

Computer Algebra club/seminar

Series
Additional Talks and Lectures
Time
Wednesday, January 21, 2026 - 13:00 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Anton LeykinGeorgia Tech

Let us discuss how to use generative AI to help with math and coding.

My presentation features two scenarios:

Coding in LaTeX. Suppose you have a raw draft of what potentially could be a math paper. We will consider and apply simple AI tools that may help realizing the potential.

Coding in CAS. Suppose you have a raw idea for a package in a Computer Algebra System; your raw idea may be limited to a rough description of the input/output of a method you would like to implement. How far can an AI assistant take you? Can it autonomously code a working software package?   

 

Some upper and lower bounds on the variance of functions of independent random variables

Series
Probability Working Seminar
Time
Tuesday, January 20, 2026 - 15:30 for 1.5 hours (actually 80 minutes)
Location
Skiles 006
Speaker
Christian HoudréGeorgia Tech

Please Note: Second of several talks.

I'll present various methods, some old, some new,  leading to estimates on the variance of $f(X_1, X_2, \dots, X_n)$ where  

$X_1, X_2, \dots, X_n$ are independent random variables.  These methods will be illustrated with various examples.

Mass inflation for spherically symmetric charged black holes

Series
PDE Seminar
Time
Tuesday, January 20, 2026 - 15:30 for 1 hour (actually 50 minutes)
Location
Skiles 254
Speaker
Onyx Gautam Princeton University

The Reissner–Nordström spacetime models a spherically symmetric and time-independent charged black hole in general relativity. The Cauchy horizon in the interior of such a black hole is subject to an infinite blueshift instability. In 1989, Poisson and Israel discovered a nonlinear manifestation of this instability in the spherically symmetric setting called "mass inflation," where the Hawking mass becomes identically infinite at the Cauchy horizon. 

We complete the first proof of mass inflation for a wave-type matter model, namely the spherically symmetric Einstein–Maxwell–scalar field system. This result follows from a large-data decay result for the scalar field in the black hole exterior combined with works of Dafermos, Luk–Oh, and Luk–Oh–Shlapentokh-Rothman.

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