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 approach is inspired by Geiger's system-amg but we use dune-istl
aggregation AMG for it. On the fine level all unknowns attached to a cell
form a matrix block and are treated fully coupled. To form the first
coarse level system we use only the pressure component to guide the aggregation
and neglect all other unknowns on the fine level. All other level are formed
in the usual way by scalar aggregation.
Currently,it has to be requested for flow_ebos manually by passing
"linear_solver_use_amg=true amg_blackoil_system=true" to it.
3x3 matrix block inversion in FieldMatrix is numerically unstable
including version 2.5.0. Therefore the previous if clause was wrong
as it activated the use of FieldMatrix already for 2.5.0 (the version
in Debian stable). With this commit we use MatrixBlock for version 2.5.0.
The specialization is added in the ISTLSolver, not in fmatrix.h in dune-
common since 1) we need it now 2) the special treatment of singular and
near singular matrices may be specifiy to the solvent model.
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.
For flow_legacy the first component a block is used, which is the
oil pressure. As flow_ebos uses different indices this commit
explicitly uses BlackoilIndices::pressureSwitchIdx to tell the AMG
at which index the pressure is stored.
This was previously deactivated because of the single precision support
of flow_legacy and missing single-precision support for UMFPack.
As flow_ebos does not use single precision this commit allows using amg
at least for flow_ebos.
These are not aware whether they are parallel or not. Therefore
the user should only specify a verbose verbosity only on one rank.
With this commit we do this on the process responsible for terminal
output.
In upstream they expect to be used with FielMatrix as
the block type only. Thus it it is impossible to use AMG
with a direct coarse solver within OPM. With this patch
it would be possible if we did not use field type float.
