PETSc

[Aron Ahmadia]

Hi Brian,

I took a quick peek at the source for DAGetGlobalVector in the current release:

"
  for (i=0; i<DA_MAX_WORK_VECTORS; i++) {
    if (da->globalin[i]) {
      *g             = da->globalin[i];
      da->globalin[i] = PETSC_NULL;
      goto alldone;
    }
  }
  ierr = DACreateGlobalVector(da,g);CHKERRQ(ierr);

  alldone:
  for (i=0; i<DA_MAX_WORK_VECTORS; i++) {
    if (!da->globalout[i]) {
      da->globalout[i] = *g;
      break;
    }
 "

The two appear to be very similar, with this exception.  Get/Restore
work with one copy of the DA's global vector, but will make a copy if
one has already been checked out or none exist.

DACreateGlobalVector will always make a copy of the global vector,
regardless of the circumstances.   I think you're better off using Get
and Restore (less data copying) unless you'd like to work with
multiple copies for some reason.

~A

On 1/27/07, Brian Grierson <bag2107 at columbia.edu> wrote:
>
> Could you please tell me the difference between
>
> DACreateGlobalVector / VecDestroy
> and
> DAGetGlobalVector / DARestoreGlobalVector
>
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> Brian A. Grierson
>
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> Department of Applied Physics
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> Columbia University
>
> Mobile: 646.259.1038
>
> Work:    212-854-4839
>
> bag2107 at columbia.edu
>
> bgrierson21 at gmail.com
>
> http://www.columbia.edu/~bag2107/http://www.apam.columbia.edu/ctx/ctx.html
>
>