# Colloquia

**UW Madison mathematics Colloquium is ONLINE on Fridays at 4:00 pm. **

# Fall 2020

## September 25, 2020, Joseph Landsberg (Texas A&M)

(Hosted by Gurevitch)

**From theoretic computer science to algebraic geometry: how the complexity of matrix multiplication led me to the Hilbert scheme of points.**

In 1968 Strassen discovered the way we multiply nxn matrices (row/column) is not the most efficient algorithm possible. Subsequent work has led to the astounding conjecture that as the size n of the matrices grows, it becomes almost as easy to multiply matrices as it is to add them. I will give a history of this problem and explain why it is natural to study it using algebraic geometry and representation theory. I will conclude by discussing recent exciting developments that explain the second phrase in the title.

## October 9, 2020, Carolina Araujo (IMPA)

(Hosted by Ellenberg)

**Symmetries in Algebraic Geometry and Cremona transformations**

In this talk I will discuss symmetries of complex algebraic varieties. When studying a projective variety $X$, one usually wants to understand its symmetries. Conversely, the structure of the group of automorphisms of $X$ encodes relevant geometric properties of $X$. After describing some examples of automorphism groups of projective varieties, I will discuss why the notion of automorphism is too rigid in the scope of birational geometry. We are then led to consider another class of symmetries of $X$, its birational self-maps. Birational self-maps of the projective space $\mathbb{P}^n$ are called Cremona transformations. Describing the structure of the group of Cremona transformations of the plane is a classical problem that goes back to the 19th century. In higher dimensions, not so much is known, and a natural problem is to construct interesting subgroups of the Cremona group. I will end by discussing a recent work with Alessio Corti and Alex Massarenti, where we investigate subgroups of the Cremona group consisting of symmetries preserving some special meromorphic volume forms.

## October 23, 2020, Jeremy Quastel (University of Toronto)

(Hosted by Gorin)

## November 6, 2020, Yiannis Sakellaridis (Johns Hopkins University)

(Hosted by Gurevitch)

## November 20, 2020, Reserved

(Hosted by Rodriguez)

## December 4, 2020, Federico Ardila (San Francisco)

(Hosted by Ellenberg)