Something weird with SNES convergence reason
Matthew Knepley
knepley at gmail.com
Thu May 15 07:28:40 CDT 2008
1) Are the linear systems really being solved in Newton?
2) What is the Bratu parameter? Turn it off and see that you
get convergence in 1 iteration.
Matt
On Wed, May 14, 2008 at 10:30 PM, Rafael Santos Coelho
<rafaelsantoscoelho at gmail.com> wrote:
> Hello everybody,
>
> I've coded a program which solves, in parallel, the three-dimensional Bratu
> problem. Afterwards, I've run tests in a cluster to see how it would go and,
> at first, it seemed ok to me, but then I've noticed that whenever I
> increased the number of processors (from 16 to 32, for example), the program
> started to diverge due to a failure in the Line Search Newton's Method. Here
> is what a monitoring function prints out:
>
> nonlinear iteration number = 1, norm(F(x)) = 1013.53, linear iterations =
> 16
> nonlinear iteration number = 2, norm(F(x)) = 1013.33, linear iterations =
> 32
> nonlinear iteration number = 3, norm(F(x)) = 1013.33, linear iterations =
> 48
> Nonlinear solve did not converge due to DIVERGED_LS_FAILURE
>
> Indeed, one can see that the method is really diverging (for smaller tests,
> though, say N = 8 * 8 * 8, it converges).
>
> What's wrong here? Is it something with my code? If yes, how can I fix it?
>
> Best regards,
>
> Rafael
>
>
--
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which
their experiments lead.
-- Norbert Wiener
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