PERFORMANCE OF THE GEM CODES ON NONSEPARABLE 5- AND 9-POINT OPERATORS

Abstract

Timing and accuracy tests of the GEM (general elliptic marching) codes are described. The GEM codes solve elliptic and mixed discretized two-dimensional partial differential equations by direct (noniterative) spatial marching methods. Both 5-point and 9-point stencils may be solved, with no requirement that the coefficients be separable, and quite general boundary conditions are treated. The basic GEM code depends on problem parameters (primarily a large cell aspect ratio Δ/Δy) to control the instability incurred in marching elliptic equations. For a 5-point operator with non-periodic boundary conditions, repeat solutions are obtained in the time equivalent of two SOR iterations. Stabilizing codes allow an increase of the problem size in the marching direction at some penalty in execution time and core storage.