Overlapping Additive Schwarz on Nonoverlapping Grids
This branch adds an overlapping additive Schwarz preconditioner implemented in a purely algebraic way on nonoverlapping grids by
- starting from an indexset with minimal overlap, construct an index set with more overlap (is based on the ParallelIndexSet class from dune-common)
- Construct a matrix on the new overlapping index set from a matrix on the minimal overlap index set
- Implement a two-level Schwarz preconditioner using the Nicolaides coarse space This means you can have overlapping Schwarz with arbitrary overlap on UGGrid and ALUGrid.