On Wed, Apr 4, 2012 at 08:13, behzad baghapour <behzad.baghapour@gmail.com> wrote:
Actually I want to change the system, applying some modifications to the solution after each Newton iteration.

in petsc-dev

http://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/SNES/SNESLineSearchSetPostCheck.html

or, in 3.2

http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/SNES/SNESLineSearchSetPostCheck.html