MatCreateMPIAIJ Pre-allocation Query

[Barry Smith]

  If your problem is so big that you need integers that represent numbers
more than about 2 billion then yes you will need to rebuild PETSc. 

  Barry

You'll be the first PETSc user who solves a problem with more than
2 billion unknowns.


On Sun, 17 Jun 2007, Tim Stitt wrote:

> Thanks for that Matt...will check it out.
> 
> Incidentally, I need to pass a 64-bit integer to MatCreateMPIAIJ. Do I need to 
> rebuild PETSc using a 64-bit integer option switch?
> 
> Tim. 
> 
> On Sunday 17 June 2007 17:07, Matthew Knepley wrote:
> > 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)
> 
>