Parallel detection and elimination of strongly connected components for radiation transport sweeps

Abstract

Discrete ordinate methods are commonly used to simulate radiation transport for fire or weapons modeling. The computation proceeds by sweeping the flux across a grid. A particular cell cannot be computed until all the cells immediately upwind of it are finished. If the directed dependence graph for the grid cells contains a cycle, then sweeping methods will deadlock. This can happen in unstructured grids and time-stepped problems where the grid is allowed to deform. We describe a parallel algorithm to detect and break these cycles present in the directed dependence graphs of these grids as well as an implementation and experimental results on shared and distributed memory machines.