Dear all, I have a lot of coefficients in my form, e.g. 1) Calculate density rhow pointwise from temperature and pressure via interpolation of a table rhow = Function(DG1) rhow.dat.data[:]=calc_rhow(temp,Tsat,pw) 2) Averaging rhow_avg = (rhow('+') + rhow('-')) / 2.0 3) Use rhow_avg in my form. This works all right for calulcating F(u), but fails when computing the Jacobian. Since I calculate things pointwise and providing all the derivatives is not so easy I use -snes_fd_color. What I would want to happen is that the function calc_rhow is called every time rhow_avg is needed. This seems not to be the case. Rather the coefficient is assumed constant and thus the derivative is zero. How can I make sure that the function calc_rhow is called every time I need rhow_avg? 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 ------------------------------------------------------