A FAST MULTILEVEL ALGORITHM FOR INTEGRAL-EQUATIONS

We show how the discretization of integral equations by composite Gaus s rules can be related to approximations of integral operators that co nverge in the operator norm, rather than strongly converge. From this norm convergent formulation a two-level approximate inverse can be con structed whose evaluation requires no fine mesh evaluations of the int egral operator. The resulting multilevel algorithm, therefore, is roug hly half as costly as the Atkinson-Brakhage iteration. The algorithm i s applicable to both linear and nonlinear equations.