Dear all, I am doing a refinement study for two-phase flow in porous media. The first five levels of refinement succeed and I get reasonable results. On level six I get an error (see [1]). I also attached the trace. I tried the suggestion with -snes_converged_reason and -ksp_converged_reason, but this gives no output. Since the error seems to originate from the projection on the linear output space, I removed these parts. Then I get [2]. Do you have an idea what I am doing wrong? Why does the formulation seem to be correct for coarse discretizations, but gives NAN for finer ones? Thank you! Henrik [1] firedrake.exceptions.ConvergenceError: Nonlinear solve failed to converge after 0 nonlinear iterations. Reason: Inner linear solve failed to converge after 0 iterations with reason: unknown reason (petsc4py enum incomplete?), try with -snes_convered_reason and -ksp_converged_reason %s""" % (snes.getIterationNumber(), msg)) [2] Nonlinear solve did not converge due to DIVERGED_FNORM_NAN iterations 0 -- 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 ------------------------------------------------------