[petsc-dev] MatDestroy call in MatMerge

[Hong Zhang]

Vaclav:

> I feel that it is quite incorrect that MatMerge calls MatDestroy(&inmat)
> since this corrupts "garbage collection" - inmat is destroyed but only
> nullified in MatMerge. It remains unchanged outside so subsequent
> MatDestroy call fails. I think that there is no reason for this destroy, if
> am right, MatMerge does not corrupt the inmat so it can be reused and then
> destroyed manually.
>
MatMerge():
 Creates a single large PETSc matrix by concatenating local sequential
                 matrices from each processor.
It was written for petsc internal use (private function), and only works
for mpiaij format. Thanks for the suggestion. I'll
remove MatDestroy(&inmat) from
MatMerge().

>
> The second question is - what is the principal difference between MatMerge
> and MatMerge_SeqsToMPI - I am confused a bit.
>
MatMerge_SeqsToMPI - Creates a MPIAIJ matrix by adding sequential
                 matrices from each processor .

>
> And I have finally one note about MatMerge_SeqsToMPI manual page: there is
> instead a synopsis of MatMerge_SeqsToMPINumeric because this comment is
> located above the MatMerge_SeqsToMPINumeric function in source.
>
I fixed this in petsc-3.2, and will merge to petsc-dev.

We may need rename these two functions for better understanding.
Thanks for the report, which helps us improve petsc library.

Hong
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