[petsc-users] (no subject)

[Reza Yaghmaie]

Dear Matt,

The initial guess was zero for all cases of SNES solvers. The initial
jacobian was identity for all cases. The system is small and is ran
sequentially.
I have to add that I use FDColoring routine for the jacobian as well.

Regards,
Ray





On Monday, May 4, 2015, Matthew Knepley <knepley at gmail.com> wrote:

> On Mon, May 4, 2015 at 5:41 PM, Reza Yaghmaie <reza.yaghmaie2 at gmail.com
> <javascript:_e(%7B%7D,'cvml','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
>> <javascript:_e(%7B%7D,'cvml','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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