Parallel Coarse-Grid Treatment in AMG for Coupled Systems

We present a parallel implementation of an agglomeration scheme for the coarse-grid treatment in algebraic multigrid algorithms for coupled systems. The association of the components of the solution vector with different physical unknowns --- bearing particular difficulties to parallel agglomeration techniques --- is considered through an appropriate re-ordering of the components of the solution vector. A benchmark of a system of mixed elliptic-hyperbolic character shows that the proposed scheme allows to apply an agglomeration technique which is significantly faster than conventional approaches based on a parallel direct solution of the coarse-grid system.