preconditioner for matrix-free linear system

[Yongcheng Zhou]

hi there,

I want to link my own package with PETSc in order to make use of its
various preconditioners.  I am using
matrix free method, so that I can directly refer the large matrix
saved in my own format. The connection
works OK without preconditioners, but runs into trouble when most of
the preconditioners is called.
For example, I got this message when using PCICC preconditionder:

Matrix format shell does not have a built-in PETSc direct solver!

So my question is how to utilize PETSc's powerful preconditioners for
my matrix-free application.

Thanks,

Rocky