[petsc-users] Prelloc: Get coordinates of local diagonal submatrix

[Florian Lindner]

Hello,

> MatGetOwnershipRangesColumn

Thanks! That's what I was looking for.

I have set a MatSetLocalToGlobalMapping on the matrix and I use

MatMPIAIJSetPreallocation(_matrixA.matrix, 0, d_nnz, 0, o_nnz)

to set the preallocation. Am I right to assume that nnz is to in the the PETSc ordering of rows and not application ordering?

Best Thanks,
Florian

Am Mittwoch, 6. April 2016, 10:19:23 CEST schrieben Sie:
> On Wed, Apr 6, 2016 at 10:12 AM, Florian Lindner <mailinglists at xgm.de>
> wrote:
> 
> > Hello,
> >
> > in order to preallocate I have to know whether a non-zero will be in the
> > local diagonal submatrix or not.
> >
> >
> > http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatMPIAIJSetPreallocation.html
> >
> > says:
> >
> > The DIAGONAL portion of the local submatrix of a processor can be defined
> > as the submatrix which is obtained by extraction the part corresponding to
> > the rows r1-r2 and columns c1-c2 of the global matrix, where r1 is the
> > first row that belongs to the processor, r2 is the last row belonging to
> > the this processor, and c1-c2 is range of indices of the local part of a
> > vector suitable for applying the matrix to. This is an mxn matrix. In the
> > common case of a square matrix, the row and column ranges are the same and
> > the DIAGONAL part is also square. The remaining portion of the local
> > submatrix (mxN) constitute the OFF-DIAGONAL portion.
> >
> > Therefore I compute the begin and end rows and cols like that:
> >
> >   int ownerRangeBeginA = _matrixA.ownerRange().first;
> >   int ownerRangeEndA = _matrixA.ownerRange().second;
> >
> >   // Uses: MatGetVecs(_matrixA.matrix, &vector, nullptr);
> >   petsc::Vector diagTest{_matrixA, "test", petsc::Vector::RIGHT};
> >
> >   int localDiagColBegin = diagTest.ownerRange().first;
> >   int localDiagColEnd = diagTest.ownerRange().second;
> >
> >   Debug("Local Submatrix Rows = " << ownerRangeBeginA << " / " <<
> > ownerRangeEndA <<
> >         ", Local Submatrix Cols = " << localDiagColBegin << " / " <<
> > localDiagColEnd);
> >
> >
> > It's a little bit tainted by my PETSc C++ helper function, but I think you
> > get the code.
> >
> > Is there a way to do it more elegantly? Without instantiating a vector
> > just for the purpose of gettings its owner range? And then testing a if an
> > index is inside the local diagonal submatrix?
> >
> 
> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatGetOwnershipRangesColumn.html
> 
>   Thanks,
> 
>      Matt
> 
> 
> > Thanks,
> > Florian
> >
> 
> 
> 
>