[petsc-users] How to do a precondition in SNES flow

[Gong Ding]

Hi all,

I'd like to do a  special jacobian precondition during the snes 
iteration, for which jacobian matrix and RHS vector must be modified 
explicitly.

In the SNESComputeJacobian, the preconditioner P is built after assembly 
of jacobian matrix.

I need to multiply P to J and RHS vector  explicitly as left 
precondition before the solve stage of J*dx = rhs.

However, I find that petsc evaluates function before jacobian, so P*RHS vector 
can not be processed at SNESComputeFunction.

As a result,  I must find a hook function after SNESComputeJacobian and before 
the solve stage.

Any suggest?

Gong Ding