[petsc-users] MatMPIAIJSetPreallocationCSR

[Oliver Browne]

>> 
>> 
>> 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


so using the above example

I should

  CALL MatMPIAIJSetPreallocationCSR(A,i,j,v)

where

i = [0, 1, 3, 6]
j = [0, 0, 2, 0 , 1 , 2]
v = [1,2,3,4,5,6]

Ollie


> 
>> 
>> 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