A simple preconditioner for electric-field integral equations

A preconditioner is applied to the electric-field integral equation, to imp rove the convergence of iterative integral-equation solvers, such as the co njugate-gradient (CG) method. The preconditioner accounts for (expansion fu nction)-(testing function) interactions in the vicinity of a given basis fu nction, requiring order N complexity for N unknowns. Example results are pr esented for microwave scattering calculations for targets in the vicinity o f a half space (soil), with results computed via a multilevel fast multipol e algorithm. (C) 2001 John Wiley & Sons, Inc.