[petsc-users] How to access the KSP objects from a PCFIELDSPLIT Schur preconditioner

[Thomas Witkowski]

I want to play around with some special type of a Schur complement 
preconditioner. It perfectly fits into PETSc's fieldsplit preconditioner 
(schur - full factorization). But for the inner solvers, I would like to 
create some MatShells. So I need to access both KSP objects, for the 
upper block (KSP(A_00)) and for the Schur complement (KSP(S)). How can I 
get these objects in my source code?

Best regards,

Thomas