Currently this is very "manual" as we are still testing stuff. Will refactor
and make it an algorithm once everything works.
What currently does work:
- All tests in MultiGridPreconditioner::runChecks for the first coarse grid
- The tests for the intergrid operators going from the first to the second
coarse grid
- (1 - P R) v == 0
- (1 - R P) v_c == 0
- A full solve with VPGCR and a two-level MG preconditioner
What hinders the rest of the tests from passing with a three-level method is the
absence of implementations of CoarsenedMatrix::Mdir and CoarsenedMatrix::Mdiag.
