[petsc-users] Preconditioner for LSC

[Elena Travaglia]

Dear PETSc users,

we would like to compare our preconditioner for the Schur complement
of a Stokes system, with the LSC preconditioner already implemented in
PETSc. Following the example in the PETSc manual, we've tried
   -fieldsplit_1_pc_type lsc -fieldsplit_1_lsc_pc_type ml
but this is not working (properly) on our problem.

On the other hand we think we have a good preconditioner for A10*A01,
so  we'd like to try
   -fieldsplit_1_pc_type lsc -fieldsplit_1_lsc_pc_type shell
but we cannot figure out how to attach our apply() routine to
the pc object of fieldsplit_1_lsc.

Can this be done in the current interface?
Or perhaps, should we call KSPGetOperators on the fieldsplit_1 solver
and attach to its Sp operator a "LSC_Lp" of type MATSHELL with our routine
attached to the MATOP_SOLVE of the shell matrix?

Thanks in advance,

Elena and Matteo

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