[petsc-users] MatSetSizes for MATMPIBAIJ

[Matthew Knepley]

On Fri, Feb 5, 2010 at 6:17 PM, NovA <av.nova at gmail.com> wrote:

> 2010/2/6 Barry Smith <bsmith at mcs.anl.gov>:
> >
> > On Feb 5, 2010, at 5:28 PM, NovA 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);
> >
> >                                                                ^^^^^^
> >                            This is wrong! Look at the manual page for
> > MatCreateMPIBAIJ() for information on the meaning of this.
>
> Sorry, but I can't find any additional info on this at
>
> http://www.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/Mat/MatCreateMPIBAIJ.html
> and around. I could just expect that those sizes mean number of blocks
> not individual values, but can't find any confirmation...
>

>From the page: It says m,n,M,N are "rows" and the values in d_nz,o_nz are
"blocks".


> >>  MatSetType(A, MATMPIBAIJ);
> >>  MatGetOwnershipRange(A, &rowS, &rowE);
> >>  Then loop local rows from rowS/4 to rowE/4 to preallocate storage
> >> using MatMPIBAIJSetPreallocation(A,4,...)
> >
> >   You cannot do it this way. You cannot call MatGetOwnershipRange()
> before
> > setting the preallocation.
>
> Oh, ok. This applies to BAIJ, right? For AIJ this works, so I thought
> it should for BAIJ either.
>

This is not correct for AIJ either.

   Matt


> >
> >   You can either,
> >
> > 1) figure out yourself the local sizes you want to use, then just call
> > MatCreateMPIBAIJ() with all the information (or call MatCreate(),
> > MatSetType(), MatSetSizes(), MatMPIBAIJSetPreallocation()) or
> > 2) Use PetscMap (see manual page for PetscMapInitialize) to see how PETSc
> > would decompose the rows and then use that information to do 1).
>
> Thanks for the tip. I'll try to sort it out.
>
> Best wishes,
>    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
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