[petsc-dev] Preconditioner for Schur complement (pcfieldsplit)

[Thomas Witkowski]

I have implemented a Schur complement solver based on the fieldsplit 
preconditioner, i.e., my code is executed with the option 
-pc_fieldsplit_type schur. How can I define a preconditioner Sp for the 
inner Schur complement solution? I want to define the preconditioner in 
an explicit way, thus build a matrix that should approximate S in some way!

Thomas