Name of the Seminar: Statistics and Probability Seminar

Day, date and time: Wednesday, 24 July 2024, 4:00 pm

Venue: Ramanujan hall

Host: Debraj Das

Speaker: Mihir Dewaskar

Affiliation: Duke University

Title: Robustifying likelihoods by optimistically re-weighting data

Abstract: Likelihood-based inferences have been remarkably successful in
wide-spanning application areas. However, even after due diligence in
selecting a good model for the data at hand, there is inevitably some
amount of model misspecification: outliers, data contamination, or
inappropriate parametric assumptions such as Gaussianity mean that most
models are at best rough approximations of reality. A significant
practical concern is that under large sample sizes, even small amounts of
model misspecification may have a substantial impact on our inferences. In
this talk, we discuss how one can robustly estimate likelihood-based
models by re-weighting terms in the likelihood. We term this as
"optimistic re-weighting" because the weights are chosen to make the
re-weighted data look like that arising from our model. We describe a
theoretically motivated alternating optimization procedure called
Optimistically Weighted Likelihood (OWL) to obtain these weights. We
describe two applications of OWL: first to estimate the average treatment
effect in a micro credit study in the presence of outliers, and second to
robustly fit a Gaussian mixture model to single cell RNA-Seq data.

Speaker: Dr. Rajat Gupta
Affilitation: University of Texas at Tyler
Title: Smallest parts function of Andrews, sum-of-tails identities: A 
combinatorial excursion
Abstract: See attached PDF file

Venue: Ramanujan Hall
Time:  14:30-15:30 hrs
Date:  26th July 2024.

Title: Smallest parts function of Andrews, sum-of-tails identities: A combinatorial excursion

Abstract:  In the first half of the talk, we first review a classical combinatorial result of Ramanujan and Uchimura, which states that the difference between the sum of the smallest parts of the partitions of n into an odd number of distinct parts and the corresponding sum for an even number of distinct parts is equal to the number of divisors of n. We will see its connection with a problem arising from the theory of random acyclic graphs. The second half will be devoted to some-of-tails identities and extensions of the above theorem with its application. The works presented here are the joint work with Rahul Kumar, Noah Lebowitz-Lockard and Professor Joseph Vandehey.

Name of the Seminar: Topology Seminar (online)

Day, date and time: Friday, 26 July 2024, 2:30-3:30 PM

Venue : Google Meet joining info
Video call link: https://meet.google.com/sun-aoda-zja

Host: Rekha Santhanam

Speaker: Sumanta Das

Affiliation: IISc, Bengaluru

Title : Strong Topological Rigidity of Non-Compact Orientable surfaces.

ABSTRACT. We prove that if a homotopy equivalence between any two non-compact orientable
surfaces without boundary is a proper map, then it is properly homotopic to a homeomorphism,
provided surfaces are neither the plane nor the punctured plane.