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

[Matthew Knepley]

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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