MatCreateMPIAIJ Pre-allocation Query

[Matthew Knepley]

On 6/17/07, Tim Stitt <timothy.stitt at ichec.ie> 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.

Basically, you run through the construction algorithm once to calculate
d_nnz and o_nnz, and then again to set values. You can see my code for
doing it in preallocateOperator() in src/dm/mesh/mesh.c.

   Matt

> Thanks in advance,
>
> Tim.
>
> --
> Dr. Timothy Stitt <timothy_dot_stitt_at_ichec.ie>
> HPC Application Consultant - ICHEC (www.ichec.ie)
>
> Dublin Institute for Advanced Studies
> 5 Merrion Square - Dublin 2 - Ireland
>
> +353-1-6621333 (tel) / +353-1-6621477 (fax) / +353-874195427 (mobile)
>
>


-- 
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