11/30/2009 Colloquium - Teresa Bailey
Lawrence Livermore National Laboratory
Title: Analysis of Massively Parallel Discrete-Ordinates Transport Sweep Algorithms with Collisions
Date: Nov 30, 2009
Location: 3105 Etcheverry Hall
Particle transport is an important physical process in many fields of study including reactor physics, medical physics, and astrophysics. The linear Boltzmann transport equation can be used as a mathematical model to describe particle transport, and is often solved using a discrete-ordinates numerical discretization of the angular independent variable. This discretization requires each angular unknown to sweep through a spatial mesh. The advent of parallel computing has led to the creation of many different parallel discrete-ordinates sweep algorithms; however, it is unclear if these algorithms can scale to 100,000’s of processors due to the inherently sequential nature of the discrete-ordinates method. We present theoretical scaling models for a variety of discrete-ordinates sweep algorithms. In these models, we pay particular attention to the way each algorithm handles collisions. A collision is defined as a processor having multiple angles ready to be swept during one stage of the sweep. The models also take into account how subdomains are assigned to processors and how angles are grouped during the sweep. We describe a data driven algorithm that resolves collisions efficiently during the sweep as well as other algorithms that have been designed to avoid collisions completely. Our models are preliminarily tested using the ARGES and AMTRAN transport codes. We then use the models to study and predict scaling trends in all of the sweep algorithms.
Teresa Bailey is a code physicist at Lawrence Livermore National Laboratory. She received her PhD in Nuclear Engineering from Texas A&M University in 2008, MS degree in Nuclear Engineering from Texas A&M University in 2006, and BS degree in Nuclear Engineering from Oregon State University in 2002. Between 2002-2006, she was a DOE Computational Science Graduate Fellow. Her research interests include computational methods for deterministic transport.