[petsc-users] Can we force SNES solver to do at least Newton step?

[David Knezevic]

Hi all,

I'm using the SNES solver for a plasticity model, and the issue I've run
into is that in some time steps the solver terminates after "NL step 0"
since the initial residual (based on the solution from the previous time
step) is below the specified tolerance.

I gather that "NL step 0" only checks the residual and doesn't actually do
a Newtown update, and hence it seems that this is leading to inaccurate
results in some cases. I can of course specify a smaller convergence
tolerance to avoid this issue, but I've found it difficult to find a
smaller tolerance that works well in all cases (e.g. it leads to too many
iterations or non-convergence). So instead what I would like to do is
ensure that the solver does at least 1 Newton iteration instead of
terminating at "NL step 0". Is there a way to enforce this behavior, e.g.
by skipping "NL step 0", or specifying a "minimum number of iterations"? I
didn't see anything like this in the documentation, so I was wondering if
there are any suggestions on how to proceed for this.

Thanks,
David
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20230902/8d914203/attachment.html>