# Events for 02/20/2020 from all calendars

## Number Theory Seminar

**Time: ** 10:30AM - 11:30AM

**Location: ** BLOC 220

**Speaker: **Nahid Walji, American University of Paris

**Title: ***On the distribution of Hecke eigenvalues in the complex plane*

**Abstract: **Let r be a cuspidal automorphic representation of non-solvable polyhedral type for GL(2) over a number field. We establish the existence of sets of primes with positive upper Dirichlet density for which the associated Hecke eigenvalues satisfy prescribed bounds on their argument and/or size. For example, if r is not self-dual we show that there is a positive upper density of Hecke eigenvalues in any sector of size 2.64 radians.

**URL: ***Event link*

## Banach and Metric Space Geometry Seminar

**Time: ** 3:00PM - 4:00PM

**Location: ** BLOC220

**Speaker: **Anastasios Sidiropoulos, University of Illinois at Chicago, Theory Group

**Title: ***Robust metric learning via geometric approximation algorithms*

**Abstract: **We study the problem of learning a metric space under discriminative constraints. Given a universe X and sets S, D of similar and dissimilar pairs in X, we seek to find a mapping f: X → Y, into some host metric space M = (Y, ρ), such that similar objects are mapped close together, and dissimilar objects are mapped to points that are far apart from each other. More generally, the goal is to find a mapping of maximum accuracy (that is, fraction of correctly classified examples). We propose approximation algorithms for various versions of this problem, for the cases of Euclidean and tree metric spaces, and for both linear and non-linear mappings. Our problem formulation leads to algorithms that are shown to be robust against poisoning attacks when learning Mahalanobis metric spaces. Finally, we also discuss the problem of learning Mahalanobis metric spaces using depth-2 neural networks.
Based on joint works with Diego Ihara Centurion, Bohan Fan, Neshat Mohammadi and Francesco Sgherzi.