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

[Satish Balay]

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