Pacific Northwest Probability Seminar
The Nineteenth Northwest Probability Seminar
November 4, 2017
Supported by the
Pacific Institute for the Mathematical
Sciences (PIMS) and
Lecture in Probability
will be delivered by
(University of Toulouse) in 2017.
The 19th Northwest Probability Seminar, a one-day mini-conference organized by the University of Washington, the Oregon State University, the University of British Columbia, the University of Oregon, and Microsoft Research, will be held on November 4, 2017. The conference will be hosted at Microsoft, supported by Microsoft Research and the Pacific Institute for the Mathematical Sciences (PIMS).
There is no registration fee. Breakfast, lunch, and coffee will be free.
The talks will take place in Building 99 at Microsoft. Parking at Microsoft is free.
Titles and abstracts
Persi Diaconis (Stanford University)
Title: An Analysis of Spatial Mixing
In joint work with Soumik Pal, we study natural mixing processes where cards (or dominoes or mahjong tiles) are 'smushed' around on a table with two hands. How long should mixing continue. If things are not well mixed, what patterns remain? We study this in practice (!): experiments indicate that about 30 seconds of smushing suffice to mix 52 cards. We also study it in theory introducing a variety of models which permit analysis. Part of the analysis passes to a reflecting, jump- diffusion limit and uses this and a novel 'shadow coupling' to give reasonably precise bounds on the mixing time.
Yevgeniy Kovchegov (Oregon State University)
Title: Random self-similar trees: dynamical pruning and its applications to inviscid Burgers equations
We introduce generalized dynamical pruning on rooted binary trees with edge lengths. The pruning removes parts of a tree $T$, starting from the leaves, according to a pruning function defined on subtrees within $T$. The generalized pruning encompasses a number of previously studied discrete and continuous pruning operations, including the tree erasure and Horton pruning. For example, a finite critical binary Galton-Watson tree with exponential edge lengths is invariant with respect to the generalized dynamical pruning for arbitrary admissible pruning function. We will discuss an application in which we examine a one dimensional inviscid Burgers equation with a piece-wise linear initial potential with unit slopes. The Burgers dynamics in this case is equivalent to a generalized pruning of the level set tree of the potential, with the pruning function equal to the total tree length. We give a complete description of the Burgers dynamics for the Harris path of a critical binary Galton-Watson tree with i.i.d. exponential edge lengths.
This work was done in collaboration with Ilya Zaliapin (University of Nevada Reno) and Maxim Arnold (University of Texas at Dallas).
Michel Ledoux (University of Toulouse)
Title: Optimal matching of Gaussian samples
Optimal matching problems are random variational problems widely investigated in
the mathematics and physics literature. We discuss here the optimal matching problem
of an empirical measure on a sample of iid random variables to the common law in
Kantorovich-Wasserstein distances, which is a classical topic in probability and statistics.
Two-dimensional matching of uniform samples gave rise to deep results investigated
from various view points (combinatorial, generic chaining). We study here the case of
Gaussian samples, first in dimension one on the basis of explicit representations of
Kantorovich metrics and a sharp analysis of more general log-concave distributions
in terms of their isoperimetric profile (joint work with S. Bobkov), and then in dimension two
(and higher) following the PDE and transportation approach recently put forward by
L. Ambrosia, F. Stra and D. Trevisan.
Yuval Peres (Microsoft Research)
Title: Gravitational allocation to uniform points on the sphere
Given $n$ uniform points on the surface of a two-dimensional sphere,
how can we partition the sphere fairly among them?
"Fairly" means that each region has the same area.
It turns out that if the given points apply a two-dimensional
gravity force to the rest of the sphere, then the basins of attraction
for the resulting gradient flow yield such a partition - with exactly
equal areas, no matter how the points are distributed.
(See the cover of the AMS Notices
Our main result is that this partition minimizes, up to a bounded factor,
the average distance between points in the same cell. I will also present
an application to almost optimal matching of $n$ uniform blue points to $n$ uniform
red points on the sphere, connecting to a classical result of
Ajtai, Komlos and Tusnady (Combinatorica 1984).
Joint work with Nina Holden and Alex Zhai.
Gourab Ray (University of Victoria)
Title: A characterization theorem for the Gaussian free field
We prove that any random distribution satisfying conformal invariance and a form of domain Markov property and having a finite moment condition must be the Gaussian free field. We also present some open problems regarding what happens beyond the Gaussian free field. Ongoing joint work with Nathanael Berestycki and Ellen Powell.
No host dinner (6:00 onwards) at
Haiku sushi & seafood buffet, downtown Redmond