[CIG-SHORT] pylith processing error

Wed Nov 28 08:36:56 PST 2012

Bobby,

You are DECREASING (tightening) the tolerances. You want to INCREASE
(loosen) the tolerances.

Brad

On Tue, Nov 27, 2012 at 3:56 PM,  <BOK10 at pitt.edu> wrote:
> Brad,
>
> Okay, I made the rtol for ksp and snes 1.0e-20, and the
> friction.zero_tolerance 1.0e-14. The snes_atol at 1.0e-16 and the ksp_atol
> at 1.0e-18. Hopefully that works.
>
> Bobby
>
>
>> Bobby,
>>
>> Keep ksp_rtol and snes_rtol small (1.0e-20).
>>
>> Keep
>> friction.zero_tolerance > ksp_atol
>> snes_atol > friction.zero_tolerance
>>
>> See the examples/3d/hex8/step14 for where to specify
>> friction.zero_tolerance.
>>
>> Regards,
>> Brad
>>
>>
>> On 11/27/2012 03:08 PM, BOK10 at pitt.edu wrote:
>>> Brad,
>>>
>>> That helped a lot, thank you!
>>>
>>> My last question for today is more specific to my problem. If i'm
>>> looking
>>> to see how long it takes to move a fault >1cm for at least 75% of the
>>> total length of the fault, what are reasonable atol/rtol values to try?
>>> I've tried a bunch of different things, but when I decrease them from
>>> their current state of atol 1.0e-12 and 1rtol 1.0e-12, the length of
>>> time
>>> it takes seems to double from estimates I had before. Though, I'm not
>>> sure
>>> that the non linear solver converged in those previous cases...
>>>
>>> Bobby
>>>
>>>
>>>> Bobby,
>>>>
>>>> When the nonlinear solve (SNES) doesn't converge, it means the solution
>>>> you are getting has error on the order of the tolerance when it
>>>> diverged. On certain parts of the domain, the error could be larger.
>>>>
>>>> Running in parallel should help reduce the time it takes to run a
>>>> simulation.
>>>>
>>>> Nonlinear solver convergence will be slow in problems with
>>>> through-going
>>>> faults and when there is fault opening due to how we update the slip
>>>> estimate when sliding occurs. In these cases there is little that can
>>>> be
>>>> done in tuning the parameters. We need to improve the nonlinear solver
>>>> to handle these problems.
>>>>
>>>> Regards,
>>>> Brad
>>>>
>>>>
>>>> On 11/27/2012 01:46 PM, BOK10 at pitt.edu wrote:
>>>>> Hi Brad,
>>>>>
>>>>> I've played around with the examples and looked at a very coarse
>>>>> problem
>>>>> with the same configuration. I also tried tuning the parameters so
>>>>> that
>>>>> it
>>>>> runs faster, which works, the only problem is that the slip rate on my
>>>>> fault is faster when I compare it to what I had before.
>>>>>
>>>>> I have my ksp_rtol at 1.0e-8 and ksp_atol at 1.0e-12. The max_it for
>>>>> the
>>>>> ksp is now 800 which seems to stop it from ever running into a problem
>>>>> in
>>>>> that regard, but the snes still won't diverge. I have the same rtol
>>>>> and
>>>>> atol values for the snes, and I've tried an snes max_it of 200 (no
>>>>> convergence), and one of 1000 (converged, but took about 35 minutes to
>>>>> process one time stamp).
>>>>>
>>>>> I guess my major question is: what does it mean when the non linear
>>>>> solver
>>>>> doesn't converge? How would this affect the results? I'm having
>>>>> difficulty
>>>>> wrapping my head around this.
>>>>>
>>>>> Thanks,
>>>>> Bobby
>>>>>
>>>>>
>>>>>> Bobby,
>>>>>>
>>>>>> I suggest playing around with the examples or a very coarse problem
>>>>>> with
>>>>>> the same configuration to try to tune the parameters so that it runs
>>>>>> faster. Also read the section on PETSc solver parameters in the
>>>>>> "Running
>>>>>> PyLith" chapter of the manual.
>>>>>>
>>>>>> Regards,
>>>>>> Brad
>>>>>>
>>>>>>
>>>>>> On 11/27/2012 12:08 PM, BOK10 at pitt.edu wrote:
>>>>>>> It looks like my KSP_max_it was off by a bit (300, but now 320). My
>>>>>>> SNES_Max_it is causing a divergence issue, and I have it set at 300.
>>>>>>> It
>>>>>>> says its not converging. My concern is that right now it take 4-5
>>>>>>> hours
>>>>>>> to
>>>>>>> process each simulation. Is there a way around this? Can I change my
>>>>>>> SNES_atol or rtol to something more reasonable?
>>>>>>>
>>>>>>> Bobby
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> Bobby,
>>>>>>>>
>>>>>>>> Your description is far too vague for us to diagnose the problem. I
>>>>>>>> suggest that you look at the usual suspects, such as is the solve
>>>>>>>> converging (use ksp_converged_reason = true and
>>>>>>>> snes_converged_reason
>>>>>>>> =
>>>>>>>> true).
>>>>>>>>
>>>>>>>> Regards,
>>>>>>>> Brad
>>>>>>>>
>>>>>>>>
>>>>>>>> On 11/27/2012 07:57 AM, BOK10 at pitt.edu wrote:
>>>>>>>>> To clarify: the vtk output (the values in it) at some point is
>>>>>>>>> identical
>>>>>>>>> to the last one to process correctly. It usually occurs in the
>>>>>>>>> latter
>>>>>>>>> part
>>>>>>>>> of the simulation, but there are a few instances where it happens
>>>>>>>>> in
>>>>>>>>> the
>>>>>>>>> first bit, then resumes normally.
>>>>>>>>>
>>>>>>>>>> Hi,
>>>>>>>>>>
>>>>>>>>>> I'm running a simulation for 400 years with a 5 year dt, and it
>>>>>>>>>> can
>>>>>>>>>> process it fine for the first half, but then sometimes it will
>>>>>>>>>> just
>>>>>>>>>> give
>>>>>>>>>> me nothing in the output files (0kb size) and the last 20-30 of
>>>>>>>>>> 80
>>>>>>>>>> vtk
>>>>>>>>>> files write really quickly and have the same exact values. Is
>>>>>>>>>> there
>>>>>>>>>> a
>>>>>>>>>> way
>>>>>>>>>> to fix this?
>>>>>>>>>>
>>>>>>>>>> Bobby
>>>>>>>>>>
>>>>>>>>>> _______________________________________________
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>>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
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>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>>
>>>>
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>>>
>>
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