[petsc-users] MatMPIAIJSetPreallocationCSR

[Barry Smith]

On May 14, 2014, at 12:27 PM, Oliver Browne <oliver.browne at upm.es> wrote:

> 
> 
> On 14-05-2014 17:34, Barry Smith wrote:
>> 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?
> 
> I am not entirely sure about this and what it means. Each processor has a portion of the 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.
> 
> So this MatMPIAIJSetPreallocationCSR call should be in some sort of loop;
> 
> Do counter =  1, No of Processors
> 
> calculate local numbering for i and isolate parts of j and v needed
> 
> Call MatMPIAIJSetPreallocationCSR(A,i,j,v)
> 
> END DO
> 
> Is this correct?

   Oh boy, oh boy.  No absolutely not. Each process is calling MatMPIAIJSetPreallocationCSR() once with its part of the data. 

  Barry

> 
> Ollie
> 
>>   Barry
>> 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