[petsc-users] Question about using MatSNESMFWPSetComputeNormU

[Matthew Knepley]

On Thu, Aug 18, 2016 at 10:39 AM, 최경준 <kyungjun.choi92 at gmail.com> wrote:

> 1) I wanna know the difference between applying option with command line
> and within source code.
> From my experience, command line option helps set other default settings
> that I didn't applied, I guess.
>

The command line arguments are applied to an object when *SetFromOptions()
is called, so in this case
you want SNESSetFromOptions() on the solver. There should be no difference
from using the API.


> 2) I made a matrix-free matrix with MatCreateSNESMF function, and every
> time I check my snes context with SNESView,
>
>     Mat Object:     1 MPI processes
>       type: mffd
>       rows=11616, cols=11616
>         Matrix-free approximation:
>           err=1.49012e-08 (relative error in function evaluation)
>           The compute h routine has not yet been set
>
> at the end of line shows there's no routine for computing h value.
> I used MatMFFDWPSetComputeNormU function, but it didn't work I think.
> Is it ok if I leave the h value that way? Or should I have to set h
> computing routine?
>

I am guessing you are calling the function on a different object from the
one that is viewed here.
However, there will always be a default function for computing h.

  Thanks,

    Matt


> Kyungjun.
>
> 2016-08-18 23:18 GMT+09:00 Matthew Knepley <knepley at gmail.com>:
>
>> On Thu, Aug 18, 2016 at 8:35 AM, 최경준 <kyungjun.choi92 at gmail.com> wrote:
>>
>>> Hi, I'm trying to set my SNES matrix-free with Walker & Pernice way of
>>> computing h value.
>>>
>>> I found above command (MatSNESMFWPSetComputeNormU) but my fortran
>>> compiler couldn't fine any reference of that command.
>>>
>>> I checked Petsc changes log, but there weren't any mentions about that
>>> command.
>>>
>>> Should I have to include another specific header file?
>>>
>>
>> We have this function
>>
>>   http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpage
>> s/Mat/MatMFFDWPSetComputeNormU.html
>>
>> but I would recommend using the command line option
>>
>>   *-mat_mffd_compute_normu*
>>
>>   Thanks,
>>
>>      Matt
>>
>> Thank you always.
>>>
>>
>>
>>
>> --
>> 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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