> Its hard to say anything without knowing what equations are being solved.
I was expecting that, but the equation is rather long to write in ascii. I do have a latex version somewhere that I can send if necessary. It is horribly nonlinear, though, including a term like (d/dx f) * (d^2/dx^2) f. > However, > does the linear problem converge? If so, you could try continuation in a > parameter > in the nonlinear term. Linear solve is fine, it starts with (SNES iteration 1) [0] KSPDefaultConverged(): Linear solver has converged. Residual norm 8.93296e-12 is less than relative tolerance 1e-05 times initial right hand side norm 9.16829 at iteration 1 and goes to (SNES iteration 107 - which is the one which diverges) [0] KSPDefaultConverged(): Linear solver has converged. Residual norm 4.10794e-06 is less than relative tolerance 1e-05 times initial right hand side norm 1.07761 at iteration 1 Decreasing ksp_rtol to 1e-15 makes no difference, so I think the problem is not in the linear solve. As to the continuation, I was trying to avoid that since I am already doing continuation in two parameters! That is because I am scanning a 2-dim parameter space. I know an exact solution for one pair of these two (namely, a straight line) and then start changing them always using the previous result as the new initial guess. I will test the continuation in the worst nonlinear parts and see what happens. Cheers, -Juha -- ----------------------------------------------- | Juha J?ykk?, juhaj at iki.fi | | http://www.maths.leeds.ac.uk/~juhaj | ----------------------------------------------- -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/pgp-signature Size: 836 bytes Desc: This is a digitally signed message part. URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20110623/f439add8/attachment.pgp>