From the manual page for PCFieldSplitGetSubKSP()
You must call KSPSetUp() before calling PCFieldSplitGetSubKSP().
Please try this and let us know if it still doesn't call your
PressureBlock().
PETSc developers: we should figure out how to have it generate a very
useful error message if the PCFieldSplitGetSubKSP() is called prematurely,
currently it sets
ierr =
PetscObjectComposeFunction((PetscObject)pc,"PCFieldSplitGetSubKSP_C",PCFieldSplitGetSubKSP_FieldSplit);CHKERRQ(ierr);
in PCCreate_FieldSplit() which is premature and will lead to errors.
Presumably we should not set this composition until the setup is called?
Barry
> On Nov 13, 2016, at 11:36 PM, Safin, Artur <[email protected]> wrote:
>
> Hello,
>
> What is the proper way to set up a shell preconditioner within a fielsplit? I
> have tried it on my own, but do not get the proper behavior. The relevant
> portion looks like this:
>
> __________________________________________________________________
> // Global System
> KSPSetOperators(ksp, A, A);
>
> // Skipped code..
>
>
> // Shell Preconditioner for the pressure sub-block
> KSP *subksp;
> PCFieldSplitGetSubKSP(pc, NULL, &subksp);
>
> Mat pressureA;
> KSPSetType(subksp[0], "preonly");
> MatCreateShell(MPI_COMM_WORLD, n_local_P_dofs, n_local_P_dofs, ,
> PETSC_DETERMINE, PETSC_DETERMINE, &pressureA);
> MatShellSetOperation(pressureA, MATOP_MULT, (void(*)(void)) PressureBlock);
> KSPSetOperators(subksp[0], pressureA, pressureA);
>
> // Skipped code..
>
>
> KSPSetUp(ksp);
> KSPSolve(ksp, b, x);
> __________________________________________________________________
>
> The fieldsplit component works fine; the solver however does not go into the
> custom function PressureBlock(), so I am curious as to what the correct
> approach is.
>
> Best,
>
> Artur
