A review of algebraic multigrid

Since the early nineties, there has been a strongly increasing demand for more efficient methods to solve large sparse, unstructured linear systems of equations. For practically relevant problem sizes, classical one-level methods had already reached their limits and new hierarchical algorithms had to be developed in order to allow an efficient solution of even larger problems. This paper gives a review of the first hierarchical and purely matrix-based approach, algebraic multigrid (AMG). AMG can directly be applied, for instance, to efficiently solve various types of elliptic partial differential equations, discretized on unstructured meshes, both in 2D and 3D. Since AMG does not make use of any geometric information, it is a \plug-in" solver which can even be applied to problems without any geometric background, provided that the underlying matrices have certain properties