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

[Justin Chang]

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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