[petsc-users] Convert mat SEQAIJ to MPIAIJ

[Thomas Witkowski]

Am 04.09.2012 17:20, schrieb Matthew Knepley:
> On Tue, Sep 4, 2012 at 9:52 AM, Thomas Witkowski 
> <thomas.witkowski at tu-dresden.de 
> <mailto:thomas.witkowski at tu-dresden.de>> wrote:
>
>>
>>     http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MATNEST.html
>>
>     As I wrote in my initial question, each rank contains one and only
>     one seqaij matrix, which all should be joined to one global matrix
>     such that each local matrix is the corresponding diagonal block of
>     the mpiaij matrix. I think, this does not work with nested matrices?
>
>
> Why does this not work? I really think you are making this harder than 
> it has to be.
>
Mh, maybe I have an incomplete view of the possibilities how to use 
nested matrices.

To become more specific: In the case of two mpi tasks, each containing 
one seqaij matrix, how to call MatCreateNest? Is this correct:

Mat A;
MatCreaeteNest(PETSC_COMM_WORLD, 2, PETSC_NULL, 2, PETSC_NULL, V ,&A);

and V is defined on rank 0 as

Mat V[2] = {seqMat, PETSC_NULL} ;

and and rank 1 as

Mat V[2] = {PETSC_NULL, seqMat};


Thomas
>    Matt
>
>     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
>>>
>>>
>
>
>
> -- 
> 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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