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Upcoming Events

Branwen Purdy at her stall during OMSI meet-a-scientist day.

Branwen Purdy prepares hands-on activities for kids at the OMSI Meet-A-Scientist Day in Portland, to share hands-on learning experiences about her research in topological data analysis.

Join us for these events hosted by the Department of Mathematics, including colloquia, seminars, graduate student defenses and outreach, or of interest to Mathematicians hosted by other groups on campus.

Access our archive of events

Cross-Multiplicative Coalescent Processes and Applications

STAG 112
Graduate Student Seminar

Speaker: Aren Lampman

The talk is based on the paper by Y. Kovchegov, P. T. Otto, and A. Yambartsev (ALEA, Lat. Am. J. Probab. Math. Stat. 18, 81–106 (2021)).Here is the original abstract:We introduce and analyze a novel type of coalescent processes called cross-multiplicative coalescent that models a system with two types of particles, A and B. The bonds are formed only between the pairs of particles of opposite types with the same rate for each bond, producing connected components made of particles of both types. We analyze and solve the Smoluchowski coagulation system of equations obtained as a hydrodynamic limit of the corresponding Marcus- Lushnikov process. We establish that the cross-multiplicative kernel is a gelling kernel, and find the gelation time. As an application, we derive the limiting mean length of a minimal spanning tree on a complete asymmetric bipartite graph with independent edge weights, distributed uniformly over [0, 1]. Read more.


Randomized Kaczmarz, Geometric Smoothing, and Momentum

STAG 163
REU Colloquium

Speaker: Nick Marshall

Abstract. This talk discusses the effect of adding geometrically smoothed momentum to the randomized Kaczmarz algorithm, which is an instance of stochastic gradient descent on a linear least squares loss function. We prove a result about the expected error in the direction of singular vectors of the matrix defining the least squares loss. We present several numerical examples illustrating the utility of our result and pose several questions. Read more.