[petsc-users] using PCFieldSplitGetSubKSP in c++

[Klaij, Christiaan]

This may be a dumb question (new to c++), well anyway: I'm trying
to get the sub KSP associated with the Schur complement S, in
order to set the null space. This is the code:

  KSP subksp[2];
  PetscInt n=2;
  ierr = PCFieldSplitGetSubKSP(pc,&n,&subksp); CHKERRQ(ierr);
  ierr = KSPSetNullSpace(subksp[1],subnullsp); CHKERRQ(ierr);

It gives the following compiler error:

error: argument of type "KSP (*)[2]" is incompatible with parameter of type "KSP **"
    ierr = PCFieldSplitGetSubKSP(pc,&n,&subksp); CHKERRQ(ierr);
                                       ^
So I changed the code to:

  KSP *subksp[2];
  PetscInt n=2;
  ierr = PCFieldSplitGetSubKSP(pc,&n,subksp); CHKERRQ(ierr);
  ierr = KSPSetNullSpace(subksp[1],subnullsp); CHKERRQ(ierr);

Now I get the error:

error: argument of type "KSP *" is incompatible with parameter of type "KSP"
    ierr = KSPSetNullSpace(subksp[1],subnullsp); CHKERRQ(ierr);
                           ^

What is the proper way to set the null space of the Schur
complement? I already have the null space of the matrix [A00 A01,
A10 A11], the null space of A11 - A10 inv(A00) A01 is clearly
related and could perhaps be deduced somehow?


dr. ir. Christiaan Klaij
CFD Researcher
Research & Development
E mailto:C.Klaij at marin.nl
T +31 317 49 33 44

MARIN
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