[firedrake] Pass approximate Jacobian to derivative() call

Dear all, is it possible to just pass the approximate Jacobian to the derivative call? Since it's so complicated in my case to get the exact Jacobian I would like to do sth. like du = [(F(u + h) - F(u - h))/(2*h)] Thank you! 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 ------------------------------------------------------