


Algebraic Stacks lecture series
Tuesday, 20 February, 11:30 AM
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Venue: Room 113
Host: Sudarshan Gurjar
Speaker: Nitin Nitsure
Affiliation: Bhaskaracharya Pratishthana
Title: Separated and proper morphisms for algebraic stacks
Abstract: This talk is devoted to the generalization of algebraic stacks of the theory of separated and proper morphisms for schemes. We will begin by recalling the relevant basics of algebraic spaces and of algebraic stacks, and their morphisms, illustrated with elementary examples. This will be followed by a description of specializations of points on algebraic stacks, which is the background needed for the valuative criteria for universal closedness and separateness.
Lecture series on Bayesian analytics
20 and 22 Feb 11:35 am to 1:00 pm
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Venues:
Ramanujan Hall on 22nd Feb.
Room 216 on 20 Feb.
Host: Radhendushka Srivastava
Speaker: Prof. Sujit Ghosh, NCSU.
Title: A short course on "Bayesian Analytics in Practice".
Abstract: The Bayesian paradigm provides a natural and practical way for building complex analytical models by expressing the joint model through a sequence of simpler conditional models, making it useful for various hierarchical data structures. This series of lectures will first introduce the general notions of Bayesian methods via hierarchical models, and then expand the topic with the more realistic and complex models that have recently emerged as a result of current Machine Learning (ML) literature. These models will be illustrated through practical applications to various real case studies avoiding much of the theoretical underpinnings. However, pointers to relevant theory will be provided as supplements with additional resources. Participants with basic knowledge of probability theory and statistical inferential framework will find the lectures useful in expanding their toolkit with the advanced use of Bayesian analytical methods. Popular topics such as prior sensitivity analysis, model comparisons, and uncertainty quantification for machine learning methods will be covered. In particular, the lectures will provide the necessary theory and practice for handling missing and censored data, a topic largely ignored in traditional ML methods. The concepts and methods discussed will be demonstrated primarily using R software illustrations, but the methodologies presented can also be carried out by other software (e.g., Python). Group activities during lab will be encouraged, allowing participants to have a handson experience.
Topology and Related Topics Seminar
Tuesday, 20 February 2024, 12:001:00
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Venue: Ramanujan Hall (Hybrid Lecture) (Speaker will be online).
Host: Rekha Santhanam
Speaker: Suraj Krishna
Affiliation: Technion  Israel Institute of Technology
Title: Cubulating hyperbolic mapping tori.
Abstract: A group is cubulated if it acts properly and cocompactly on a CAT(0) cube complex, which is a generalisation of a product of trees. Cubulated groups possess remarkable algebraic and geometric features and are an important topic of study in geometric group theory. In this talk, I will show that semidirect products of hyperbolic groups with $\mathbb{Z}$, which are themselves hyperbolic, are cubulated.
Two prominent examples of our setup are: (1) Mapping tori of fundamental groups of closed hyperbolic surfaces over pseudoAnosov automorphisms, and (2) Mapping tori of free groups over atoroidal automorphisms.
Both of these classes of groups are known to be cubulated due to outstanding works. Our proof builds upon these two noteworthy results and places them in a unified framework. This is based on joint work with François Dahmani and Jean Pierre Mutanguha.
Algebraic Groups Seminar
Tuesday, February 20, 4 pm
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Venue: Ramanujan Hall
Host: Shripad M. Garge
Speaker: Shripad M. Garge
Affiliation: IIT Bombay, Mumbai
Title: Homogeneous Spaces  II
Abstract: We study homogeneous spaces for linear algebraic groups.
Commutative Algebra Seminar
Tuesday, 20 Feb, 4 pm—5 pm
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Venue: Room 215
Host: Tony J. Puthenpurakal
Speaker: Sudeshna Roy
Affiliation: TIFR Bombay
Title: Epsilon multiplicity in twodimensional standard graded algebras
Abstract: The notion of epsilon multiplicity, a generalization of the HilbertSamuel multiplicity, was introduced by B. Ulrich and J. Validashti to detect the integral dependence of arbitrary ideals. This invariant is difficult to handle as there are examples where it can be irrational and the epsilon function is very far from being polynomiallike. Let $A$ be a standard graded normal domain of dimension two over a field with the unique homogeneous maximal ideal $m$. Let $I$ be a homogeneous ideal in $A$. Our objective is to show that the epsilon multiplicity of $I$ is a rational number.