[petsc-dev] DMGetMatrix --> DMGetMatrices?

[Matthew Knepley]

On Fri, Feb 10, 2012 at 3:08 PM, Dmitry Karpeev <karpeev at mcs.anl.gov> wrote:

>
>
> On Fri, Feb 10, 2012 at 12:13 AM, Jed Brown <jedbrown at mcs.anl.gov> wrote:
>
>> On Fri, Feb 10, 2012 at 00:05, Dmitry Karpeev <karpeev at mcs.anl.gov>wrote:
>>
>>> I don't think so.  Preallocating doesn't set any values and seems to
>>> leave the matrix marked !assembled.
>>> MatDuplicate for such a matrix will fail.  Assemblying it before setting
>>> values (just to force an assembled flag)
>>> will squeeze out the extra values, won't it?  I think it would just be
>>> reasonable to allow to duplicate unassembled
>>> matrices, or, better yet, have a matrix be "assembled" by default until
>>> MatSetValues has been called.
>>> But I'm not sure whether either solution will break something else.
>>>
>>
>> Are you calling DMSetMatrixPreallocateOnly()?
>>
>> What I'm talking about is an implementation issue, rather than a question
> of what the user should expect from the DMGetMatrix API: I have a matrix
> that has been preallocated by libMesh based on its mesh connectivity, but
> it
> has not been assembled. If I didn't want to return it in DMGetMatrix, but
> rather to duplicate it, Id be out of luck:
> that matrix is not "assembled", hence, cannot be duplicated.  This, in
> fact, has little to do with the DM interface.
> The question is: should we be able to duplicate such "unassambled"
> matrices? Or should they even be call "unassembled"?
>

In fact, preallocated matrices, obtained from DMGetMatrix, can be copied.
If that solves the problem, we are done.

   Matt


> Dmitry.
>
-- 
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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