MatCreateMPIAIJ Pre-allocation Query

[Barry Smith]

  Tim,

   It is possible the macros MatPreallocateInitialize(), ... in petscmat.h
are exactly what you need.

   Barry

Take a look at DAGetMatrix2d_MPIAIJ() in src/dm/da/utils/fdda.c for 
an example of how they can be used.


On Sun, 17 Jun 2007, Tim Stitt wrote:

> Hi All,
> 
> Currently I am using MatCreateMPIAIJ to create a distributed sparse matrix for 
> use in my parallel sparse eigensolver. If I understand things correctly, it 
> is important to specify the correct pre-allocation values for (o_nz,d_nz) or 
> (o_nnz, d_nnz) respectively to obtain optimum memory usage per node.
> 
> For information my matrix redistribution routine generates each row in the 
> sparse matrix (associated with a given node) "on-the-fly" and then uses 
> MatSetValues to apply the elements.
> 
> My question is: does anyone have a standard code template for the calculating 
> the d_nz or d_nnz values (along with o_nz or o_nnz respectively) so that 
> optimum pre-allocation is obtained? Is there a simple way of determining if a 
> given non-zero value in a row is part of the diagonal or off-diagonal regions 
> for a given distributed topology?
> 
> Any assistance gratefully received.
> 
> Thanks in advance,
> 
> Tim.
>  
>