Both ILU0 and ILUT preconditioners can apply to any non-degenerate matrix. They can be used alone or together with the
RCI FGMRES solver (see
Sparse Solver Routines
). Avoid using these preconditioners with MKL RCI CG solver because in general, they produce a non-symmetric resulting matrix even if the original matrix is symmetric. Usually, an inverse of the preconditioner is required in this case. To do this the
triangular solver routine
must be applied twice: for the lower triangular part of the preconditioner, and then for its upper triangular part.