[petsc-users] Problem with KSPGetPC within FieldSplit context

[Lucia Barandiaran]

Dear PETSc community,

We recently updated PETSc libraries and came across with a problem with 
FieldSplit preconditioning (our code is implemented in Fortran 90).

In the older version, when calling PCFieldSplitGetSubKSP we declared the 
subksp array as KSP and it worked perfectly. However, now we must 
declare it as a Fortran pointer and allocate it before 
calling PCFieldSplitGetSubKSP otherwise the code won't compile...

With the new modification, that part of the code is the following:

****Variable declarations

       PetscInt              ::  n_splits_retrieved
       IS                    ::  IS_field(max_field)
       KSP, pointer :: subksp_array(:)
       PC                    ::  subpc(max_field)
       INTEGER(iwp)          ::  nfield, ifield

**** FieldSplit Part ****

    !    Allocate Fortran array to hold the KSP contexts
         ALLOCATE(subksp_array(n_splits_retrieved))

    !    Second call to get the actual KSP contexts
         CALL PCFieldSplitGetSubKSP(solver%pc, n_splits_retrieved, &
                                    subksp_array, ierr)

         IF (n_splits_retrieved >= 2) THEN
           DO ifield = 1, n_splits_retrieved

           ! Configure the KSP for the velocity block (field 0)
             CALL KSPGetPC(subksp_array(ifield), subpc(ifield), ierr)
             CALL KSPSetType(subksp_array(ifield), KSPGMRES, ierr)
             CALL PCSetType(subpc(ifield), PCJACOBI, ierr)
           ! Allows runtime options for sub-KSP
             CALL KSPSetFromOptions(subksp_array(ifield), ierr)
           ! Choose a viewer (stdout for example)
!           viewer = PETSC_VIEWER_STDOUT_WORLD
!           CALL PCView(subpc(ifield),viewer,ierr)
           END DO
         END IF

When debugging the fortran code we observed that it stops with an error 
when calling KSPGetPC  and we can't figure out what are we doing 
wrong... Maybe we need an interface when calling that function?

Thanks very much for your time,

Sincerely,

Lucía Barandiarán

Scientific software developer  - Dracsys

Collaborator at MECMAT group - Universitat Politècnica de Catalunya (UPC)
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