[CIG-SHORT] PyLith Convergence issue - DIVERGED_FUNCTION_COUNT and CONVERGED_SNORM_RELATIVE

[Josimar Alves da Silva]

Dear Brad, Matt and Charles,

I am working on a 2-D quasi-static, elastic, simulation using rate and
state friction model.

The simulation runs fine for many time steps, then at some point I get the
error below related to DIVERGED_FUNCTION_COUNT.

Nonlinear solve did not converge due to DIVERGED_FUNCTION_COUNT iterations
5000

All the log files, along with the .cfg files, model geometry and boundary
conditions as well as a convergence plot for the SNES residual can be found
on the attached .zip file.

I have some questions that I would like to have your input:

1) Is it possible to extend the maximum value for DIVERGED_FUNCTION_COUNT
 ? Note that I have snes_max_it = 10000  but SNES still stops at 5000 value.

2) Looking at the convergence plots that I have attached, I noticed that
the time step that fails contains iterations that actually increase the
residual,instead of decreasing it. Would you know what is causing this
behavior ?

3) There are several time steps that converge with tolerances smaller than
what I ask for using the snes_atol (see figure attached). At these time
steps I get the following

Line search: Aborted due to ynorm < stol*xnorm (9.933794721748e-10 <
1.046238089915e-09) and inadequate full step.

Nonlinear solve converged due to CONVERGED_SNORM_RELATIVE iterations 694

Note that I am using snes_error_if_not_converged = true.

Could you please comment on why this is happening and how I would fix this
issue ? Does it affect the next time steps after it ?

Let me know if you need any further information.

Thank you so much for you help in advance,
Best
Josimar
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