On residual smoothing in ILUM-type preconditioning

Incomplete block factorisations are used to construct flexible preconditioners for iterative linear solvers. In practice these approaches have shown to be very effective and robust. Especially they are more suitable for parallel computer architectures when comparing to classic ILU preconditioning. In this paper we introduce residual smoothing into the forward/backward substitution in order to compensate the element dropping in the Schur complement