[petsc-users] (no subject)

[Matthew Knepley]

On Mon, May 4, 2015 at 5:57 PM, Reza Yaghmaie <reza.yaghmaie2 at gmail.com>
wrote:

>
> 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.
>

So, the initial Jacobian was the identity, but we have no idea how close
that is to the true Jacobian. You could use the
coloring routines (the default) combined with


http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/SNES/SNESQNSetScaleType.html

using Jacobian, which sets the initial guess to the true Jacobian. That
would give us an idea whether the initial guess
impacted QN covergence.

  Thanks,

     Matt


> 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>
>> 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
>>
>


-- 
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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