[CIG-SHORT] PyLith Convergence issue - DIVERGED_FUNCTION_COUNT and CONVERGED_SNORM_RELATIVE
Josimar Alves da Silva
jsilva.mit at gmail.com
Fri Jun 23 06:24:17 PDT 2017
Brad,
Just to let you know that I sorted it out this problem.
I set "open_free_surface=True" instead of False. My understanding
regarding why it was not working is because I am applying tensile tractions
on the fault to balance out the normal stress, however this could
potentially cause a problem with the fault node that is on edge of the
domain (right side on the fault, on the interface between the displacement
BC and the zero displacement BC of my geometry). Do you think this could
potentially be the problem ? I
I haven't changed anything on the solver parameterization. You can find all
the log files and the pylith_parameters.json file here:
https://www.dropbox.com/sh/by2vgqadgbsk1fs/AACENG_kCXygHa3dsdEyNAf-a?dl=0
thank you,
Josimar
On Thu, Jun 22, 2017 at 5:49 PM, Josimar Alves da Silva <
jsilva.mit at gmail.com> wrote:
> Brad,
>
> Thanks for the remind. Here it is: https://www.dropbox.com/
> sh/sxiburbvru670n3/AAD3sLLHVPp-E-FKo4oQwf23a?dl=0
>
> thank you
> Josimar
>
> On Thu, Jun 22, 2017 at 5:28 PM, Brad Aagaard <baagaard at usgs.gov> wrote:
>
>> Josimar,
>>
>> Please send the pylith_parameters.json file that PyLith generates.
>>
>> Thanks,
>> Brad
>>
>>
>> On 06/22/2017 02:19 PM, Josimar Alves da Silva wrote:
>>
>>> Matt,
>>>
>>> Thanks for the help. Here is the log file with more information:
>>> https://www.dropbox.com/s/qnpk055o9xg38j1/log.out?dl=0
>>>
>>> Let me know if you need anything else.
>>>
>>> thank you,
>>> Josimar
>>>
>>> On Thu, Jun 22, 2017 at 3:21 PM, Matthew Knepley <knepley at rice.edu
>>> <mailto:knepley at rice.edu>> wrote:
>>>
>>> On Thu, Jun 22, 2017 at 12:10 PM, Josimar Alves da Silva
>>> <jsilva.mit at gmail.com <mailto:jsilva.mit at gmail.com>> wrote:
>>>
>>> Matt,
>>>
>>> Thank you so much for the help. I followed up on your
>>> suggestions:
>>>
>>> 1) Using snes_max_funcs=10000 did not help. The simulation does
>>> not go beyond iteration #5000. It stopped at the same time step
>>> as the previous one.
>>>
>>>
>>> Note this has to be in the [petsc] section. Please add snes_view.
>>> Then we can see exactly what the setting were.
>>> It would also be good to add snes_converged_reason
>>>
>>> I looked at the log. It makes as much as progress as it will ever
>>> make after 2 iterates, thus I think there
>>> is a problem with interplay of tolerances here.
>>>
>>> 2) Can you comment a little bit on how can I improve my initial
>>> guess, as you mentioned here : "if your initial guess is not
>>> good enough they can fail". What you mean about it ?
>>>
>>>
>>> I mean if you are taking time steps so big that the last solution is
>>> not close to the next one, the solves will be harder.
>>>
>>> Matt
>>>
>>> The log file is attached.
>>>
>>> thank you so much in advance,
>>> Josimar
>>>
>>>
>>>
>>>
>>> On Thu, Jun 22, 2017 at 11:33 AM, Matthew Knepley
>>> <knepley at rice.edu <mailto:knepley at rice.edu>> wrote:
>>>
>>> On Wed, Jun 21, 2017 at 6:25 PM, Josimar Alves da Silva
>>> <jsilva.mit at gmail.com <mailto:jsilva.mit at gmail.com>> wrote:
>>>
>>> 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.
>>>
>>>
>>>
>>> snes_max_funcs 10000
>>>
>>> 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 ?
>>>
>>>
>>> There is no guarantee of decrease with a general nonlinear
>>> problem.
>>>
>>> 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
>>>
>>>
>>> This means that even a very short step length gave no
>>> residual decrease, also known as "stagnation". Here is the
>>> nonlinear
>>> solver is just not working.
>>>
>>> We have no convergence theory for the friction problems, and
>>> if your initial guess is not good enough they can fail. We
>>> want to explore
>>> more powerful solvers for these, but after we get a revised
>>> formulation in place.
>>>
>>> Thanks,
>>>
>>> Matt
>>>
>>> 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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