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# Events for 09/20/2019 from all calendars

## Probability Seminar

## Mathematical Physics and Harmonic Analysis Seminar

## Student/Postdoc Working Geometry Seminar

## Algebra and Combinatorics Seminar

## Geometry Seminar

**Time:** 11:30AM - 12:30PM

**Location:** BLOC 628

**Speaker:** Jiayan Ye (Prelim exam), TAMU

**Title:** *On Stationary DLA.*

**Abstract:** Diffusion limited aggregation (DLA) in $\mathbb{Z}^2$ is a stochastic process first defined by Witten and Sander in order to study aggregation systems governed by diffusive laws. In this talk, I will construct an infinite stationary DLA on the upper half planar lattice. The stationary DLA is ergodic with respect to integer left-right translations. This is a joint work with Eviatar Procaccia and Yuan Zhang.

**Time:** 1:50PM - 2:50PM

**Location:** BLOC 628

**Speaker:** Junho Yang, Texas A&M University, Statistics

**Title:** *Rate of convergence in Szego limit theorems*

**Abstract:** We discuss an improved rate of convergence of eigenvalues of Hermitian Toeplitz matrices originated from Szego's limiting eigenvalue distribution theorem. The proof consists of two steps: 1) provide point-wise asymptotics of all eigenvalues of banded Hermitian matrices; 2) Approximate general n-by-n Toeplitz matrix with p-diagonal banded Hermitian matrix in the sense of the "best predictive" function, and provide an entrywise 1-norm error bound. Our results can be used to calculate the exact bound of the Whittle's likelihood approximation, and approximations for the inverse of Toeplitz matrices.

Joint work with Suhasini Subbarao (TAMU Statistics).

**Time:** 2:00PM - 3:00PM

**Location:** BLOC 624

**Speaker:** A. Huang, TAMU

**Title:** *Ein and Lazarsfeld on work of Aprodu, Farkas, Papadima, Raicu and Weyman*

**Abstract:** This will be an exposition of arXiv:1906.05429

**Time:** 3:00PM - 3:50PM

**Location:** BLOC 628

**Speaker:** Gillian Grindstaff, University of Texas

**Title:** *Geometric comparison of phylogenetic trees with different leaf sets*

**Abstract:** The metric space of phylogenetic trees defined by Billera, Holmes, and Vogtmann, which we refer to as BHV space, provides a natural geometric setting for describing collections of trees on the same set of taxa. However, it is sometimes necessary to analyze collections of trees on non-identical taxa sets (i.e., with different numbers of leaves), and in this context it is not evident how to apply BHV space. Davidson et al. recently approached this problem by describing a combinatorial algorithm extending tree topologies to regions in higher dimensional tree spaces, so that one can quickly compute which topologies contain a given tree as partial data. In this talk, based on joint work with Megan Owen, I'll present an extension algorithm for metric trees inspired by their approach, which inverts a natural projection on tree space called tree dimensionality reduction (TDR). This algorithm can be used to define and search a space of possible supertrees and, for a collection of tree fragments with different leaf sets, to measure their compatibility.

**Time:** 4:00PM - 5:00PM

**Location:** BLOC 628

**Speaker:** A. Conner, TAMU

**Title:** *Border Apolarity of tensors and matrix multiplication*

**Abstract:** I will present a new method for border rank lower bounds of tensors which exploits continuous symmetry. I will discuss new results from this method's application to the matrix multiplication tensor, whose border rank is fundamentally related to the complexity of matrix multiplication.

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