[petsc-users] Question about using MatSNESMFWPSetComputeNormU

[최경준]

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.

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?


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/manualpages/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
>
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