Incomplete LU (ILU) preconditioner using the near-field matrix of the fast multipole method (FMM) is investigated to increase the efficiency of the iterative conjugate gradient squared (CGS) solver. Unlike the conventional LU, ILU requires no fill-ins hence no extra memory and CPU time in computing the LU decomposed preconditioner. It is shown that due to the nature of the near-field matrix, ILU preconditioning decreases the number of iterations dramatically.
