[petsc-users] Question about using MatSNESMFWPSetComputeNormU

[최경준]

I got stuck at FormJacobian stage.

- call SNESComputeJacobianDefault(snes, v, J, pJ, FormResidual, ier)  --> J
& pJ are same with A matrix-free matrix (input argument)



with these kind of messages..

[0]PETSC ERROR: No support for this operation for this object type
[0]PETSC ERROR: Mat type mffd



Guess it's because I used A matrix-free matrix (which is mffd type) into pJ
position.

Is there any solution for this kind of situation?


2016-08-19 2:05 GMT+09:00 Matthew Knepley <knepley at gmail.com>:

> On Thu, Aug 18, 2016 at 12:04 PM, 최경준 <kyungjun.choi92 at gmail.com> wrote:
>
>> Then in order not to use preconditioner,
>>
>> is it ok if I just put A matrix-free matrix (made from MatCreateSNESMF())
>> into the place where preA should be?
>>
>
> Yes, but again the solve will likely perform very poorly.
>
>   Thanks,
>
>      Matt
>
>
>> The flow goes like this
>> - call SNESCreate
>> - call SNESSetFunction(snes, r, FormResidual, userctx, ier)
>> - call MatCreateSNESMF(snes, A, ier)
>> - call SNESSetJacobian(snes, A, A, FormJacobian, userctx, ier)
>> - call SNESSetFromOptions()
>>
>> - call SNESGetKSP(snes, ksp, ier)
>> - call KSPSetType(ksp, KSPGMRES, ier)
>> - call KSPGetPC(ksp, pc, ier)
>> - call PCSetType(pc, PCNONE, ier)
>> - call KSPGMRESSetRestart(ksp, 30, ier)
>>
>> - call SNESSolve()
>> .
>> .
>>
>>
>> and inside the FormJacobian routine
>> - call SNESComputeJacobian(snes, v, J, pJ, userctx, ier)  --> J and pJ
>> must be pointed with A and A.
>>
>>
>>
>> Thank you again,
>>
>> Kyungjun.
>>
>> 2016-08-19 1:44 GMT+09:00 Matthew Knepley <knepley at gmail.com>:
>>
>>> On Thu, Aug 18, 2016 at 11:42 AM, 최경준 <kyungjun.choi92 at gmail.com> wrote:
>>>
>>>> Thanks for your helpful answers.
>>>>
>>>> Here's another question...
>>>>
>>>> As I read some example PETSc codes, I noticed that there should be a
>>>> preconditioning matrix (e.g. approx. jacobian matrix) when using
>>>> MatCreateSNESMF().
>>>>
>>>> I mean,
>>>> after calling MatCreateSNESMF(snes, A, ier),
>>>> there should be another matrix preA(preconditioning matrix) to use
>>>> SNESSetJacobian(snes, A, preA, FormJacobian, ctx, ier).
>>>>
>>>>
>>>> 1) Is there any way that I can use matrix-free method without making
>>>> preconditioning matrix?
>>>>
>>>
>>> Don't use a preconditioner. As you might expect, this does not often
>>> work out well.
>>>
>>>
>>>> 2) I have a reference code, and the code adopts
>>>>
>>>> MatFDColoringCreate()
>>>> and finally uses
>>>> SNESComputeJacobianDefaultColor() at FormJacobian stage.
>>>>
>>>> But I can't see the inside of the fdcolor and I'm curious of this
>>>> mechanism. Can you explain this very briefly or tell me an example code
>>>> that I can refer to. ( I think none of PETSc example code is using
>>>> fdcolor..)
>>>>
>>>
>>> This is the default, so there is no need for all that code. We use naive
>>> graph 2-coloring. I think there might be a review article by Alex Pothen
>>> about that.
>>>
>>>   Thanks,
>>>
>>>     Matt
>>>
>>>
>>>>
>>>> Best,
>>>>
>>>> Kyungjun.
>>>>
>>>> 2016-08-19 0:54 GMT+09:00 Matthew Knepley <knepley at gmail.com>:
>>>>
>>>>> 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
>>>>>
>>>>
>>>>
>>>
>>>
>>> --
>>> 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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