Past Probability Seminars Spring 2020
Thursdays in 901 Van Vleck Hall at 2:25 PM, unless otherwise noted.
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Thursday, September 11, Van Vleck B105, Melanie Matchett Wood, UW-Madison
Please note the non-standard room.
Title: The distribution of sandpile groups of random graphs
The sandpile group is an abelian group associated to a graph, given as the cokernel of the graph Laplacian. An Erdős–Rényi random graph then gives some distribution of random abelian groups. We will give an introduction to various models of random finite abelian groups arising in number theory and the connections to the distribution conjectured by Payne et. al. for sandpile groups. We will talk about the moments of random finite abelian groups, and how in practice these are often more accessible than the distributions themselves, but frustratingly are not a priori guaranteed to determine the distribution. In this case however, we have found the moments of the sandpile groups of random graphs, and proved they determine the measure, and have proven Payne's conjecture.
Thursday, September 18, Jonathon Peterson, Purdue University
Title: Hydrodynamic limits for directed traps and systems of independent RWRE
We study the evolution of a system of independent random walks in a common random environment (RWRE). Previously a hydrodynamic limit was proved in the case where the environment is such that the random walks are ballistic (i.e., transient with non-zero speed [math]$v_0 \neq 0$)[/math]. In this case it was shown that the asymptotic particle density is simply translated deterministically by the speed $v_0$. In this talk we will consider the more difficult case of RWRE that are transient but with $v_0=0$. Under the appropriate space-time scaling, we prove a hydrodynamic limit for the system of random walks. The statement of the hydrodynamic limit that we prove is non-standard in that the evolution of the asymptotic particle density is given by the solution of a random rather than a deterministic PDE. The randomness in the PDE comes from the fact that under the hydrodynamic scaling the effect of the environment does not ``average out and so the specific instance of the environment chosen actually matters.
The proof of the hydrodynamic limit for the system of RWRE will be accomplished by coupling the system of RWRE with a simpler model of a system of particles in an environment of ``directed traps. This talk is based on joint work with Milton Jara.
Thursday, September 25, Sean O'Rourke, University of Colorado Boulder
Title: Singular values and vectors under random perturbation
Abstract: Computing the singular values and singular vectors of a large matrix is a basic task in high dimensional data analysis with many applications in computer science and statistics. In practice, however, data is often perturbed by noise. A natural question is the following. How much does a small perturbation to the matrix change the singular values and vectors?
Classical (deterministic) theorems, such as those by Davis-Kahan, Wedin, and Weyl, give tight estimates for the worst-case scenario. In this talk, I will consider the case when the perturbation is random. In this setting, better estimates can be achieved when our matrix has low rank. This talk is based on joint work with Van Vu and Ke Wang.
Thursday, October 2, Jun Yin, UW-Madison
Title: Anisotropic local laws for random matrices
Abstract: In this talk, we introduce a new method of deriving local laws of random matrices. As applications, we will show the local laws and some universality results on general sample covariance matrices: TXX^*T^* (where $T$ is non-square deterministic matrix), and deformed Wigner matrix: H+A (where A is deterministic symmetric matrix). Note: here $TT^*$ and $A$ could be full rank matrices.
Thursday, October 9, No seminar due to Midwest Probability Colloquium
No seminar due to Midwest Probability Colloquium.
Thursday, October 16, TBA
Thursday, November 6, Vadim Gorin, MIT
Friday, November 7, Tim Chumley, Iowa State University
Thursday, November 13, TBA