user's own preconditioner for PCG

[Shao-Ching Huang]

Hi,

In a parallel PCG solve, is there a way to instruct PETSc to call my own 
(serial) solver to invert the per-process, local precondition matrix (as 
in the block-Jacobi preconditioner)?

Is there an example/documentation that I can follow? Which part of code 
should I start looking at?

We are trying to determine if there is any value to use the 
aforementioned customized preconditioner as compared to the general ones 
in PETSc and to DMMG, for this particular matrix at hand. This is a 
structured mesh problem.

Thank you.

Shao-Ching