A parallelized multilevel fast multipole algorithm (MLFMA) is presented for simulating electromagnetic scattering from complex targets with anisotropic impedance surfaces. By employing both surface electric and magnetic currents as unknowns and weakly enforcing the anisotropic impedance boundary condition, a combined integral equation is formulated to generate a set of well-conditioned linear systems to be solved by MLFMA. To further improve the iterative convergence of the linear systems, a parallel sparse approximate inverse preconditioner is constructed from the near-field interaction of the system matrix. The MLFMA is parallelized to enable computation on a large number of processors for large-scale problems. Several numerical examples are presented to validate the algorithm and demonstrate its accuracy, scalability, and capability in handling large complex objects with anisotropic impedance surfaces.
ÃG.r; r 0 / X.r 0 /d r 0113 construction would be more time consuming. An extensive analysis of the tradeoff between sparsity and effectiveness can be found in [23,24]. In our implementation, the sparsity pattern of the column of the SAI preconditioner associated with a given RWG is defined by retaining all the RWGs within its neighbouring cubes (including itself). If we define the indices of the nonzero columns of M asthe least-squares solution for problems (13) would involve only Q Z.W; J /. If we further denote the set of indices corresponding to the nonzero rows of Q Z.W; J / as I because the null rows do not affect the least-squares solution, the final least-squares problems can be expressed as min ke j .J / Q Z.I; J /m j .J /k 2 ; j D 1; 2; : : : ; N:Because, in MLFMA, the unknowns are grouped together by leaf cubes, it suffices to solve a single problem for each leaf cube, which is very convenient for the parallelization of MLFMA.