# Spring 2023 Colliquia

### February 3, 2023

#### Malena Espanol, Assistant Professor of Mathematics, Arizona State University

**Computational Methods for Inverse Problems in Imaging**

**Time:** 4:00 pm **Location:** JCC 270 **Reception:** JCC 501 5:00 pm **Abstract:** Discrete linear and nonlinear inverse problems arise from many different imaging systems. These problems are ill-posed, which means, in most cases, that the solution is very sensitive to the data. Because the data usually contain errors produced by different imaging system parts (e.g., cameras, sensors, etc.), robust and reliable regularization methods need to be developed for computing meaningful solutions. In some imaging systems, massive amounts of data are produced making the data storage and computational cost of the inversion process intractable. In this talk, we will see different imaging systems, we will formulate the corresponding mathematical models, we will introduce regularization methods, and we will show some numerical results.

### March 3, 2023

#### Dawei Chen, Professor of Mathematics, Boston College

**Counting Geodesics On Flat Surfaces**

**Time:** 4:00 pm **Location:** JCC 180 **Reception:** JCC 501 5:00 pm **Abstract:** A holomorphic differential induces a flat metric with saddle points such that the underlying Riemann surface can be realized as a polygon whose edges are pairwise identified by translation. Varying such flat surfaces by affine transformations induces an action on moduli spaces of differentials, called Teichmueller dynamics. Generic flat surfaces in an orbit closure of Teichmueller dynamics possess similar properties from the viewpoint of counting geodesics of bounded lengths, whose asymptotic growth rates satisfy a formula of Siegel--Veech type. In this talk Professor Chen will give a introduction to this topic and discuss some recent results about computing Siegel--Veech constants via intersection theory on moduli spaces.

### March 16, 2023

#### Eric Grinberg, U Mass Boston

**Why Reprove It? (or Theorems Which Keep on Giving)**

**Time:** 3:00 pm **Location: **Anderson 206 **Reception:** JCC 501 4:00 pm **Abstract: **Some theorems are discovered, proved and, one hopes, remembered, invoked and cited. Others are proved and reproved, again and again. The latter type is getting increasing attention. We'll explore this phenomenon through 2+1 theorems in geometry and linear algebra, and ponder reasons to reprove. The talk will include audience participation. Bring a sheet of paper and prepare to draw a large triangle and an angle or two (protractor optional). Save the backside for row reducing a matrix, or aim your device to SageMath.

### Martin Guterman Lecture 2023

#### April 7, 2023

**Steven Strogatz, Department of Mathematics, Cornell University, (Professor Strogatz is also a New York Times columnist on mathematics.)**

**Infinite Powers: **The Story of Calculus **Time:** 4:00 pm **Location:** JCC 270 **Reception:** JCC 501 5:00 pm **Abstract: **Everyone has heard of calculus, but why is it so important? In this talk, Prof. Strogatz will try to clarify the fantastic idea at the heart of calculus. With the help of pictures and stories, he’ll trace where calculus came from and then show how it – in partnership with science, engineering, philosophy, and medicine – changed the course of civilization and helped make the world modern. This talk is intended for everyone, whether you've taken calculus or not, and whether you like math or not. By the end, Prof. Strogatz hopes to convince you that calculus is one of the greatest triumphs of human creativity ever.