Incomplete LU Preconditioning Strategies for MLFMA

This paper shows that the ILU preconditioners can be used in the iterative solutions of scattering problems. It is deduced that ILU(0) can be safely applied to CFIE, yielding very close performance to the exact solution of the near-field matrix. For EFIE, establishing condest to be a strong indicator for the quality of the resulting ILU preconditioner, the following strategy is proposed. Before the iterations begin, compute condest for ILUT. If the condition estimate is not very high, (e.g., less than 10⁴), use ILUT as the preconditioner. Otherwise, switch to ILUTP5. With this strategy, robust and effective preconditioners are obtained for the test problems