An Operator Smoothing with ILU(0) for Aggregation-based Algebraic Multigrid

Due to the potential optimal convergence, algebraic multigrid is widely used in solving large sparse linear systems. The aggregation-based version is one of the widely used methods for its cheap cost and easy implementation. But its convergence is often slow compared to other versions. In this paper, a smoothing technique based on incomplete LU factorization without fill-in is presented to the operators on each level. Each operator is approximately factorized, and the derived lower and upper triangular factors are approximately inverted, which are applied to the operator from both sides to improve the diagonal dominance, and then the effectiveness of the smoothing process and the accuracy of the grid transfer operators. The numerical results show that when incorporated into the preconditioned conjugate gradient iteration, the convergence rate is greatly improved, and though the time used for setup is larger, the time used for iteration and the overall time can also be reduced for large-scale systems.