how do you access the nonzero elements in SeqAIJ matrices

[Zi-Hao Wei]

On Mon, Aug 4, 2008 at 10:53 PM, Ahmed El Zein <ahmed at azein.com> wrote:
> my code looks like:
>    ierr = MatCreate(PETSC_COMM_WORLD,&A); CHKERRQ(ierr);
>    ierr = MatSetSizes(A,M,N,M,N); CHKERRQ(ierr);
>    ierr = MatSetType(A, MATSEQAIJ); CHKERRQ(ierr);
>    ierr =  MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY); CHKERRQ(ierr);
>    [...lots of MatSetValue() calls...]
>    ierr = MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY); CHKERRQ(ierr);

I think that the code should be
  ierr = MatCreate(PETSC_COMM_WORLD,&A); CHKERRQ(ierr);
  ierr = MatSetSizes(A,M,N,M,N); CHKERRQ(ierr);
  ierr = MatSetType(A, MATSEQAIJ); CHKERRQ(ierr);
  [...lots of MatSetValue() calls...]
  ierr = MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY); CHKERRQ(ierr);
  ierr = MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY); CHKERRQ(ierr);

The routines MatAssemblyBegin and MatAssemblyEnd should be called
after completing all calls to MatSetValues().