[petsc-users] 2-stage preconditioner

[Qin Lu]

Hello,
 
I need to implement a 2-stage preconditioner using PETSc linear solver:
 
1. The first stage uses a user-provided preconditioner routine. It seems I can 
set it with PCShellSetApply.
2. The second stage uses PETSc's ILU.
 
Shall I just call this two preconditioners in sequence, or there is a 
particular way to hook them up? Is there any sample code for this?
 
Many thanks for your suggestions.
 
Best Regards, 
Qin