[petsc-users] Customizeing MatSetValuesBlocked(...)

[Jed Brown]

PETSc does NOT use a 2D partition. You need to get that concept out of your
head.

On Wed, Aug 8, 2012 at 3:09 PM, Jinquan Zhong <jzhong at scsolutions.com>wrote:

> Satish,
>
> I looked at
>
> http://www.mcs.anl.gov/petsc/petsc-current/src/snes/examples/tutorials/ex5s.c.html
> where
>
> MatCreateAIJ(PETSC_COMM_WORLD,rend-rstart,rend-rstart,N,N,5,0,0,0,&J);
>
> was used to create J (N,N) with local J dimensioned as
> (rend-rstart,rend-rstart).
>
> For my application, I have LDA=LDB=3 and N=9 in the following
>
>         ierr = MatCreateAIJ(PETSC_COMM_WORLD,LDA,LDB,N,N,LDA,0,0,0,&A);
> CHKERRQ(ierr);
>
> I got the following error message:
>
> [0]PETSC ERROR: --------------------- Error Message
> ------------------------------------
> [0]PETSC ERROR: Nonconforming object sizes!
> [0]PETSC ERROR: Sum of local lengths 27 does not equal global length 9, my
> local length 3
>   likely a call to VecSetSizes() or MatSetSizes() is wrong.
>
>
> It does NOT appear PETSc  had the 9x9 matrix. It tried to build 27*27
> since I am using 9 procs.  Is there a way to resolve this local size and
> global size issue?
>
> Thanks,
>
> Jinquan
>
>
>
> -----Original Message-----
> From: petsc-users-bounces at mcs.anl.gov [mailto:
> petsc-users-bounces at mcs.anl.gov] On Behalf Of Satish Balay
> Sent: Wednesday, August 08, 2012 1:45 PM
> To: PETSc users list
> Subject: Re: [petsc-users] Customizeing MatSetValuesBlocked(...)
>
> On Wed, 8 Aug 2012, Jed Brown wrote:
>
> > On Wed, Aug 8, 2012 at 2:25 PM, Jinquan Zhong <jzhong at scsolutions.com
> >wrote:
> >
> > > If I understand you correctly, ScaLAPACK blocks don't have anything
> > > to do with the sparse matrix structure.****
> > >
> > > ** **
> > >
> > >
> > > ********************************************************************
> > > ********************************************************************
> > > **
> > > ****
> > >
> > > ** **
> > >
> > > You are correct.  What I meant was how to define the diagonal and
> > > off-diagonal parts of each submatrix matrix  A (LDA, LDB).  For
> > > example, in the following matrix,****
> > >
> > > ** **
> > >
> > >                                   *Proc0* *Proc1*       *Proc2*****
> > >
> > >             1  2  0  |  0  3  0  |  0  4****
> > >
> > >     *Proc0*   0  5  6  |  7  0  0  |  8  0****
> > >
> > >             9  0 10  | 11  0  0  | 12  0****
> > >
> > >     -------------------------------------****
> > >
> > >            13  0 14  | 15 16 17  |  0  0****
> > >
> > >     *Proc3*   0 18  0  | 19 20 21  |  0  0      <=== owned by  Proc
> 5****
> > >
> > >             0  0  0  | 22 23  0  | 24  0****
> > >
> > >     -------------------------------------****
> > >
> > >     *Proc6*  25 26 27  |  0  0 28  | 29  0****
> > >
> > >                      30  0  0  | 31 32 33  |  0  34****
> > >
> > > ** **
> > >
> > > I am not sure how to fill out the values for d_nz, d_nnz,o_nz, o_nnz
> > > peoperly for the subblock (0 0 ;0 0; 24 0) owned by Proc 5 since it
> > > was based on diagonal and off-diagonal parts.
> > >
> >
> > Throw your 2D block cyclic nonsense out the window. These are sparse
> > matrices and that layout would be terrible. Logically permute your
> > matrices all you want, then define a global ordering and chunk it into
> > contiguous blocks of rows (no partition of columns). Work this out
> > with a pencil and paper. You should have a function that translates
> > row/column pairs from your ordering to our ordering. Now compute the
> > sparsity pattern in the new ordering. (Usually you can figure this out
> > on paper as well.) Then preallocate and call MatSetValues() with the new
> (row,column) locations.
> >
>
> also check the 'example usage' at:
>
>
> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatCreateAIJ.html
>
> Satish
>
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