[petsc-users] MatMPIAIJSetPreallocationCSR

Barry Smith bsmith at mcs.anl.gov
Wed May 14 11:34:10 CDT 2014

  See the manual page for MatMPIAIJSetPreallocationCSR() it gives an explicit simple example 

      The format which is used for the sparse matrix input, is equivalent to a
    row-major ordering.. i.e for the following matrix, the input data expected is
    as shown:

        1 0 0
        2 0 3     P0
        4 5 6     P1

     Process0 [P0]: rows_owned=[0,1]
        i =  {0,1,3}  [size = nrow+1  = 2+1]
        j =  {0,0,2}  [size = nz = 6]
        v =  {1,2,3}  [size = nz = 6]

     Process1 [P1]: rows_owned=[2]
        i =  {0,3}    [size = nrow+1  = 1+1]
        j =  {0,1,2}  [size = nz = 6]
        v =  {4,5,6}  [size = nz = 6]

   The column indices are global, the numerical values are just numerical values and do not need to be adjusted. On each process the i indices start with 0 because they just point into the local part of the j indices.

    Are you saying each process of yours HAS the entire matrix? If so you just need to adjust the local portion of the i vales and pass that plus the appropriate location in j and v to the routine as in the example above.


On May 14, 2014, at 8:36 AM, Oliver Browne <oliver.browne at upm.es> wrote:

> On 14-05-2014 15:27, Barry Smith wrote:
>> On May 14, 2014, at 7:42 AM, Oliver Browne <oliver.browne at upm.es> wrote:
>>> Hi,
>>> I am using MatMPIAIJSetPreallocationCSR to preallocate the rows, columns and values for my matrix (efficiency). I have my 3 vectors in CSR format. If I run on a single processor, with my test case, everything works fine. I also worked without MatMPIAIJSetPreallocationCSR, and individually input each value with the call MatSetValues in MPI and this also works fine.
>>> If I want to use MatMPIAIJSetPreallocationCSR, do I need to separate the vectors for each processor as they have done here;
>>   What do you mean by “separate” the vectors? Each processor
>> needs to provide ITS rows to the function call. You cannot have
>> processor zero deliver all the rows.
> I mean split them so they change from global numbering to local numbering.
> At the moment I just have
> CALL MatMPIAIJSetPreallocationCSR(A,NVPN,NNVI,CONT,ierr) - 3 vectors have global numbering
> How can submit this to a specific processor?
> Ollie
>>   Barry
>>> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatMPIAIJSetPreallocationCSR.html#MatMPIAIJSetPreallocationCSR
>>> Thanks in advance,
>>> Ollie

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