[petsc-users] petscviewerbinaryread

[Matthew Knepley]

On Mon, Jun 17, 2013 at 10:59 AM, Frederik Treue <frtr at fysik.dtu.dk> wrote:

> Hi guys,
>
> is petscviewerbinaryread working? The examples given at the webpage
> either fails with out of memory error issues (ex65 and ex65dm) or
> doesn't compile (ex61) for me?
>
> Oddly I have problems only when trying to use mpi. My code:
>
>
> ierr=DMDACreate1d(PETSC_COMM_WORLD,DMDA_BOUNDARY_GHOSTED,156,1,1,PETSC_NULL,&da);CHKERRQ(ierr);
>
> ierr=DMCreateGlobalVector(da,&ReRead);CHKERRQ(ierr);
>
> ierr=VecAssemblyBegin(ReRead);CHKERRQ(ierr);
> ierr=VecAssemblyEnd(ReRead);CHKERRQ(ierr);
>
> double *workarray=(double*)malloc(156*sizeof(double));
>
> ierr = VecGetArray(ReRead,&workarray); CHKERRQ(ierr);
>

1) This does not make sense. You allocate an array, but then overwrite that
array with the one inside the vector ReRead.


>
> ierr=PetscViewerBinaryOpen(PETSC_COMM_WORLD,"./testvector",FILE_MODE_READ,&fileview);CHKERRQ(ierr);
>
> ierr=PetscViewerBinaryRead(fileview,&dummy,1,PETSC_SCALAR);CHKERRQ(ierr);
>
>
> ierr=PetscViewerBinaryRead(fileview,(void*)workarray,156,PETSC_SCALAR);CHKERRQ(ierr);
> printf("TEST: %g\n",workarray[144]);
> ierr=VecRestoreArray(ReRead,&workarray);
>

2) In parallel, the local array in your vector ReRead will be smaller than
the global size 156. Thus this read also
    does not makes sense.

   Matt


> VecView(ReRead,PETSC_VIEWER_DRAW_WORLD);
>
> This works fine as long as I'm on a single processor. The file read also
> works on mpi with 2 processors, as evidenced by the result of the printf
> statement (which gives the right result from both processors). However
> the VecView statement fails with "Vector not generated from a DMDA!".
> Why?
>
> And second question: How do I generalize to 2d? Can I give a 2d array to
> PetscViewerBinaryRead and expect it to work? And how should it be
> malloc'ed? Or does one give a 1d array to PetscViewerBinaryRead and let
> VecRestoreArray do the rest? Or what?
>
> /Frederik Treue
>
>


-- 
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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