AMGCL is a header-only C++ library for solving large sparse linear systems with
algebraic multigrid (AMG) method. AMG is one of the most effective iterative
methods for solution of equation systems arising, for example, from discretizing
PDEs on unstructured grids. The method can be used as a black-box solver for
various computational problems, since it does not require any information about
the underlying geometry. AMG is often used not as a standalone solver but as a
preconditioner within an iterative solver (e.g. Conjugate Gradients, BiCGStab,
or GMRES).

WWW: https://github.com/ddemidov/amgcl