[petsc-users] MatSetSizes for MATMPIBAIJ

[Matthew Knepley]

On Fri, Feb 5, 2010 at 5:28 PM, NovA <av.nova at gmail.com> wrote:

> Thanks for the quick response!
>
> 2010/2/6 Matthew Knepley <knepley at gmail.com>:
> > 1) It will distribute block rows, so you will get 8 and 4 as you want
>
> How can it distribute in such a way, if it doesn't know block size yet?
> Let's continue the example:
>   MatCreate(comm, &A);
>   MatSetSizes(A, PETSC_DECIDE,12, 12,12);
>   MatSetType(A, MATMPIBAIJ);
>   MatGetOwnershipRange(A, &rowS, &rowE);
>  Then loop local rows from rowS/4 to rowE/4 to preallocate storage
> using MatMPIBAIJSetPreallocation(A,4,...)
>
> What will be the rowS and rowE here? I think they can be not divisible
> by 4 (block size)...
>

You have to set the block size.

  Matt


> >
> > 2) Warning: This is an incredibly small problem. Using 2 processors
> >     might not show any speedup at all.
> Sure! It's just an example. I suppose it'll be much slower on two
> processors actually.
>
>
> Regards!
>  Andrey
>
> >
> >   Matt
> >
> > On Fri, Feb 5, 2010 at 5:03 PM, NovA <av.nova at gmail.com> wrote:
> >>
> >> Hi everybody!
> >>
> >> I'm looking for the best way to distribute MPIBAIJ matrix among
> >> several processors.
> >>
> >> For example, I have square matrix 3x3 of blocks 4x4 each (i.e. 12x12
> >> values) and need to distribute it among 2 processors. The generic way
> >> of creating such a matrix would be:
> >>  Mat A;
> >>  MatCreate(comm, &A);
> >>  MatSetSizes(A, loc_rows,12, 12,12);
> >>  MatSetType(A, MATMPIBAIJ);
> >>
> >> What is the optimal value for loc_rows here?
> >>
> >> Can I use PETSC_DECIDE for it? I suppose this will lead to division by
> >> 6 rows per processor, which is not consistent with block size. How
> >> MatMPIBAIJSetPreallocation(A,4,...) will deal with it?
> >>
> >> Most likely, I have to manually set loc_rows to 8 and 4 according to
> >> the processor rank. But probably I miss some more clean way, when
> >> PETSc really decides. :)
> >>
> >> Thanks in advance for any comments.
> >>
> >> Regards!
> >>  Andrey
> >
> >
> >
> > --
> > 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
> >
>



-- 
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
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