On Wed, Mar 23, 2011 at 20:07, Matthew Knepley <knepley at gmail.com> wrote:
> It looks like this FD derivative did not give any descent directions when > factored. Possibly > the FD Jacobian is too inaccurate, or the factorization was. These both > mean your problem > is very ill-conditioned. You should try to reformulate it. > Yes, it is often possible to reformulate to make the system better scaled. You can also run with -snes_fd_type ds which uses a more robust method of computing the step, sometimes this make a difference. If you know the sparsity pattern of the Jacobian, you can use coloring to "efficiently" assemble a sparse Jacobian using only residual evaluation. There are many examples that do this. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20110324/72c527f2/attachment-0001.htm>
