[petsc-users] Convert mat SEQAIJ to MPIAIJ

[Thomas Witkowski]

Am 04.09.2012 16:20, schrieb Hong Zhang:
> Thomas:
> Do you mean create a mpiaij matrix of order 2nx2n from two local nxn 
> matrices?
Yes.
> You might have to use MatSetValues() to do this.
I think, it will be faster and more efficient to create a MatShell to 
wrap around the local matrices. If anybody has some other ideas, please 
let me know.

Thomas


>
> Hong
>
>>
>>     Thomas :
>>
>>         In my FETI-DP code, each rank creates a SEQAIJ matrix that
>>         represents the discretization of the interior domain. Just
>>         for debugging, I would like to join these sequential matrices
>>         to one global MPIAIJ matrix. This matrix has no off diagonal
>>         nnzs and should be stored corresponding to the ranks
>>         unknowns, thus, first all rows of the first rank and so on.
>>         What's the most efficient way to do this? Is it possible to
>>         create this parallel matrix just as a view of the sequential
>>         ones, so without copying the data? Thanks for any advise.
>>
>>
>>     http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatCreateMPIAIJConcatenateSeqAIJ.html
>>
>>     Note: entries in seqaij matrices are copied into a mpiaij matrix
>>     without
>>     inter-processor communication. Use petsc-3.3 for this function.
>
>     The function does not do what I expect. For example, if we have
>     two mpi task and each contains one local square matrix with n
>     rows, I want to create a global square matrix with 2n rows. This
>     function create a non-square matrix of size 2n x n.
>
>     Thomas
>
>

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