Currently we run into issues with the parallel AMG if
redistribution happened on the coarsest level. That is
not detected by AMG and it will construct smoothers on
all processors present before the redistribution. Some of
them will get OwnerOverlapCommunication objects that have
an invalid MPI communicator in them (MPI_COMM_NULL) and an
MPI_ERROR will be raised as we communicate in the constructor.
With this patch we detect this situaton and set the pointer to
OwnerOverlapCommunication to null to prevent communication. A
sanity check that the matrix has zero rows has been added.
This seems to have been forgotten previously. Now the code int CPRPreconditioner.hpp
uses ParallelOverlappingILU0 instead of SeqILU[0n]/BlockPreconditioner which
makes the code more slim.
The versions are missing the specialized code for inverting
a 3x3 matrix that makes the algorithms quite a bit more stable.
With this patch we fall back to using our own MatrixBlock that does
not suffer from this deficiency.
