[petsc-users] Insert values into matrix using MatSetValuesStencil or MatSetValuesLocal

[Matthew Knepley]

On Tue, Aug 25, 2015 at 10:19 AM, Wee Beng Tay <zonexo at gmail.com> wrote:

> Hi,
>
> So can I use multigrid directly if using matsetvalues stencil?
>
Do you mean, if you use MatSetStencil() then you statements will work no
matter what grid comes in to your residual function?
That is true.

  Thanks,

     Matt

> Thanks
>
>
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> On Tue, Aug 25, 2015 at 10:11 AM, Matthew Knepley <knepley at gmail.com>
> wrote:
>
> On Mon, Aug 24, 2015 at 9:01 PM, Wee Beng Tay <zonexo at gmail.com> wrote:
>
>>
>>
>> Sent using CloudMagic
>> <https://cloudmagic.com/k/d/mailapp?ct=pa&cv=7.2.9&pv=5.0.2>
>> On Mon, Aug 24, 2015 at 6:21 PM, Matthew Knepley <knepley at gmail.com>
>> wrote:
>>
>> On Mon, Aug 24, 2015 at 4:09 AM, Wee-Beng Tay <zonexo at gmail.com> wrote:
>>
>>> Hi,
>>>
>>> I'm modifying my 3d fortran code from MPI along 1 direction (z) to MPI
>>> along 2 directions (y,z)
>>>
>>> Previously I was using MatSetValues with global indices. However, now
>>> I'm using DM and global indices is much more difficult.
>>>
>>> I come across MatSetValuesStencil or MatSetValuesLocal.
>>>
>>> So what's the difference bet the one since they both seem to work
>>> locally?
>>>
>>
>> No. MatSetValuesLocal() takes local indices. MatSetValuesStencil() takes
>> global vertex numbers.
>>
>>
>> So MatSetValuesStencil() takes global vertex numbers. Do you mean the
>> natural or petsc ordering?
>>
>
> There is no PETSc ordering for vertices, only the natural ordering.
>
> Thanks,
>
> Matt
>
>> Which is a simpler/better option?
>>>
>>
>> MatSetValuesStencil()
>>
>>> Is there an example in Fortran for MatSetValuesStencil?
>>>
>>
>> Timothée Nicolas shows one in his reply.
>>
>> Do I also need to use DMDAGetAO together with MatSetValuesStencil or
>>> MatSetValuesLocal?
>>>
>>
>> No.
>>
>> Thanks,
>>
>> Matt
>>
>>> Thanks!
>>>
>>
>>
>>
>> --
>> 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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