[petsc-dev] DMGetMatrix --> DMGetMatrices?

[Dmitry Karpeev]

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"?

Dmitry.
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