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Re: MatCreateMPIAIJ Pre-allocation Query

On 6/17/07, Tim Stitt <timothy.stitt@xxxxxxxx> 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)




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