[petsc-users] Use previous solution when encountering "DIVERGED_LINE_SEARCH"

[Justin Chang]

Also, -snes_stol does not seem to work for vinewtonrsls?

On Wed, Nov 30, 2016 at 8:54 PM, Justin Chang <jychang48 at gmail.com> wrote:

> Generally speaking, yes. But this is VIRS where I am enforcing maximum
> principles. From what I have seen, the residual typically exhibit this
> behavior if there are very few violations in the first place.
>
> How would I "terminate on stagnation"?
>
> On Wed, Nov 30, 2016 at 8:48 PM, Matthew Knepley <knepley at gmail.com>
> wrote:
>
>> On Wed, Nov 30, 2016 at 8:38 PM, Justin Chang <jychang48 at gmail.com>
>> wrote:
>>
>>> By manually terminating I meant setting -snes_max_it to 5 if I know DIVERGED_LINE_SEARCH
>>> occurs after 6 iterations. In a transient simulation I cannot do this
>>>
>>
>> Let me elaborate. I mean that using DIVERGED_LINE_SEARCH as an indication
>> of convergence is dicey. It may be that in the problem
>> you looked at this was true, but I see no reason to believe its true in
>> general. Why does your residual quit decreasing?
>>
>>   Thanks,
>>
>>      Matt
>>
>>
>>> On Wed, Nov 30, 2016 at 8:35 PM, Matthew Knepley <knepley at gmail.com>
>>> wrote:
>>>
>>>> On Wed, Nov 30, 2016 at 8:27 PM, Justin Chang <jychang48 at gmail.com>
>>>> wrote:
>>>>
>>>>> Hi all,
>>>>>
>>>>> I am running some transient simulations using SNESVINEWTONRSLS. At
>>>>> certain timesteps, I get a "DIVERGED_LINE_SEARCH" which essentially
>>>>> "resets" my solution to zero and messes everything up. I notice that this
>>>>> happens when the SNES Function norm no longer decreases, and if I were to
>>>>> manually terminate the solver right before the final iteration I get the
>>>>> answer I want.
>>>>>
>>>>
>>>> Yes, its possible, however isn't that a dangerous way to terminate?
>>>> Couldn't you terminate on stagnation?
>>>>
>>>>   Thanks,
>>>>
>>>>      Matt
>>>>
>>>>
>>>>> Is there a way to "detect" this error and use the solution from the
>>>>> previous non-failing iteration? Setting a fixed maximum iteration doesn't
>>>>> seem reasonble because every time level will require different numbers of
>>>>> iterations to converge.
>>>>>
>>>>> Thanks,
>>>>> Justin
>>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> 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
>>>>
>>>
>>>
>>
>>
>> --
>> 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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