[petsc-users] (no subject)

[Matthew Knepley]

On Mon, May 4, 2015 at 5:41 PM, Reza Yaghmaie <reza.yaghmaie2 at gmail.com>
wrote:

>
> Dear Matt,
>
> Actually the initial jacobian was identity. Regular SNES converges in 48
> iterations, GMRES in 19, NCG in 67,...
> Do you think SNESQN with the basiclineseach was the problem for divergence?
> If I use SNESQN by default should not it converge with initial identity
> jacobian?
>

Do you mean that you used an initial guess of the identity, or that the
Actual Jacobian was the identity at your
initial guess?

  Matt


> Best regards,
> Reza
>
>
>
>
> On Monday, May 4, 2015, Matthew Knepley <knepley at gmail.com> wrote:
>
>> On Mon, May 4, 2015 at 2:11 PM, Reza Yaghmaie <reza.yaghmaie2 at gmail.com>
>> wrote:
>>
>>>
>>> Dear PETSC representatives,
>>>
>>> I am solving a nonlinear problem with SNESNGMRES and it converges faster
>>> with less iterations compared to otehr SNES methods. Any idea why that is
>>> the case?
>>>
>>
>> It is impossible to tell with this information.
>>
>>
>>> Also SNESQN diverges quickly. I tried to use SNESLINESEARCHBASIC for
>>> the linesearch option and nothing changes.
>>>
>>
>> This can happen, especially if your matrix is far from the identity.
>>
>>
>>> I presume it is using the default SNESQN method. Btw, there are three
>>> options for QN, as "SNES_QN_LBFGS, SNES_QN_BROYDEN, SNES_QN_BADBROYEN"
>>> in teh manual. I tried to associate them with SNES however it seems these
>>> hyphened names don't work there. What am I missing?
>>>
>>
>> -snes_qn_scale_type <lbfgs,broyden,badbroyden>
>>
>> from
>> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/SNES/SNESQNSetType.html
>>
>>    Thanks,
>>
>>     Matt
>>
>> Best regards,
>>> Ray
>>>
>>
>>
>>
>> --
>> 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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