Mon, June 22, 2020
Public Access

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June 2020
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3:00pm [3:00pm] Krishna Hanumanthu:Chennai Mathematical Institute, Chennai
Date and Time: Monday, 22 June, 3pm to 4pm IST (joining time: 2.50pm IST) Google Meet link: Speaker: Krishna Hanumanthu Affiliation: Chennai Mathematical Institute, Chennai Title: Seshadri constants and rationality questions. Abstract: Seshadri constants are a local measure of positivity of line bundles and have many interesting applications. An important question is whether Seshadri constants can be irrational. While the answer is expected to be yes, currently we do not know any examples of irrational Seshadri constants. In this talk, we will start with basics on Seshadri constants and discuss important results and connections to well known questions. We will then focus on rationality questions and exhibit irrational Seshadri constants assuming some conjectures are true. The talk will be based on two joint works, one with B. Harbourne and another with L. Farnik, J. Huizenga, D. Schmitz and T. Szemberg. I will try to keep most of the talk accessible to anyone with knowledge of basic algebraic geometry.

4:00pm [4:00pm] Dr. Pranabendu Misra (Max Planck Institute for Informatics, Saarbrucken, Germany)
Speaker: Dr. Pranabendu Misra (Max Planck Institute for Informatics, Saarbrucken, Germany) Date-time: Monday (June 22), 4-5 PM (Webex Meeting details below) Title: A 2-Approximation Algorithm for Feedback Vertex Set in Tournaments Abstract ----------- A Tournament is a directed graph T such that every pair of vertices is connected by an arc. A Feedback Vertex Set is a set S of vertices in T such that T−S is acyclic. We consider the Feedback Vertex Set problem in tournaments, where the input is a tournament T and a weight function w:V(T)→N and the task is to find a feedback vertex set S in T minimizing w(S). We give the first polynomial time factor 2 approximation algorithm for this problem. Assuming the Unique Games conjecture, this is the best possible approximation ratio achievable in polynomial time. Meeting link: Meeting number:166 483 6041 Password:RKypRMZy888