[firedrake] Modifying diagonal entries of Jacobian (preconditioning)

Dear Firedrakers, if I wanted to modify the diagonal entries of my Jacobian in a Newton step during a time step... How would I do this? Do I have to define my own preconditioner here? Henrik -- Dipl.-Math. Henrik Büsing Institute for Applied Geophysics and Geothermal Energy E.ON Energy Research Center RWTH Aachen University ------------------------------------------------------ Mathieustr. 10 | Tel +49 (0)241 80 49907 52074 Aachen, Germany | Fax +49 (0)241 80 49889 ------------------------------------------------------ http://www.eonerc.rwth-aachen.de/GGE hbuesing@eonerc.rwth-aachen.de ------------------------------------------------------