A fast preconditioner for radiative transfer equation

Speaker: 

Yimin Zhong

Institution: 

UT Austin

Time: 

Monday, April 10, 2017 - 4:00pm to 5:00pm

Host: 

Location: 

RH 306

We propose in this work a fast numerical algorithm for solving the equation of
radiative transfer (ERT) in isotropic media. The algorithm has two steps. In the first
step, we derive an integral equation for the angularly averaged ERT solution by taking
advantage of the isotropy of the scattering kernel, and solve the integral equation
with a fast multipole method (FMM). In the second step, we solve a scattering-free
transport equation to recover the original ERT solution. Numerical simulations are
presented to demonstrate the performance of the algorithm for both homogeneous and
inhomogeneous media.

Title: Universality for algorithms to compute the (extreme) eigenvalues of a random matrix

Speaker: 

T. Trogdon

Institution: 

UCI

Time: 

Thursday, March 16, 2017 - 2:00pm

Location: 

RH 340P

Abstract: The Toda lattice, beyond being a completely integrable dynamical system, has many important properties.  Classically, the Toda flow is seen as acting on a specific class of bi-infinite Jacobi matrices.  Depending on the boundary conditions imposed for finite matrices, it is well known that the flow can be used as an eigenvalue algorithm. It was noticed by P. Deift, G. Menon and C. Pfrang that the fluctuations in the time it takes to compute eigenvalues of a random symmetric matrix with the Toda, QR and matrix sign algorithms are universal. In this talk, I will present a proof of such universality for the Toda and QR algorithms and the power method.  This is joint work with P. Deift.

The Dirichlet problem for the Lagrangian phase operator

Speaker: 

Sebastien Picard

Institution: 

Columbia University

Time: 

Tuesday, May 23, 2017 - 4:00pm to 5:00pm

Location: 

RH 306

The Lagrangian phase operator arises in the study of calibrated geometries and the deformed Hermitian-Yang-Mills equation in complex geometry. We study a local version of these geometric problems, and solve the Dirichlet problem for the Lagrangian phase operator with supercritical phase given the existence of a subsolution. They key step is to find hidden concavity properties in order to obtain a priori estimates. This is joint work with T. Collins and X. Wu.

How do we parametrize a random fractal curve?

Speaker: 

Greg Lawler

Institution: 

University of Chicago

Time: 

Friday, February 24, 2017 - 2:00am to 3:00am

Host: 

Location: 

NS2 1201

For a smooth curve, the natural paraemtrization

is parametrization by arc length.  What is the analogue

for a random curve of fractal dimension d?  Typically,

such curves have Hausdorff dmeasure 0.  It turns out

that a different quantity, Minkowski content, is the

right thing.   

 

I will discuss results of this type for the Schramm-Loewner

evolution --- both how to prove the content is well-defined

(work with M. Rezaei) and how it relates to the scaling

limit of the loop-erased random walk (work with F. Viklund

and C. Benes).

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