We introduced two runtime parameters for this: ilu_redblack and
ilu_reorder_spheres. If the last one is false, we try to preserve
the ordering within in the colors. Otherwise we try to achieve a D2
(alternative diagonal) ordering.
These versions are inspired by the ones used in SuperLU and the enums
to choose them have simuilar names, but without leading S (MILU_1-MILU_3).
The following variants are supported (chosen by the enum MILU_VARIANT):
ILU: plain ILU
MILU_1: lump diagonal with dropped row entries.
MILU_2: lump diagonal with the sum of the absolute values of the dropped row
entries.
MILU_3: if diagonal is positive add sum of dropped row entrires. Otherwise substract them.
MILU_4: if diagonal is positive add sum of dropped row entrires. Otherwise do nothing
Using the parameter ilu_milu=true|false (default=false) the user can now choose
to use the modified ILU0 decomposition. If selected values will
not be dropped for nonzero entries but added to the diagonal of U.
This approach will result in A*e = L*U*e for vector e with all entries
beging 1.
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.
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.
The class is not limited to parallel preconditioners. To reflect this
we rename it to AdditionalObjectDeleter. As it will also be used for
the parallel interleaved version we move the class to a separate header.
The whole system consists out of three equations per cell. Using
the parallel index set of the grid cells for it is wrong. Therefore
we use PR OPM/opm-core#803 to set up an additional parallel index set
for the whole system and use this for the communication that is needed e.g.
by the ILU preconditioner.
Previously only passed the parallel information to the ILU preconditioner,
but of course needs this information to set up the communication, too.
With this commit we pass the parallel information object to AMG's constructor.
As with opm-core we use boost::any to provide additional
information about a parallel run. It is used to set a
ParallelISTLInformation object and and fill it with the
information obtained from a parallel Cpgrid.
Note that the simulator currently compiles sucessfully. Still,
we have to test the runs and do debugging.
