A simple preconditioner for electric-field integral equations

A preconditioner is applied to the electric-field integral equation, to improve the convergence of iterative integral-equation solvers, such as the conjugate-gradient (CG) method. The preconditioner accounts for (expansion function)-(testing function) interactions in the vicinity of a given basis function, requiring order N complexity for N unknowns. Example results are presented for microwave scattering calculations for targets in the vicinity of a half space (soil), with results computed via a multilevel fast multipole algorithm.