PETSc

[Aron Ahmadia]

Sounds like a documentation bug to me, are you referring to this?
http://www-unix.mcs.anl.gov/petsc/petsc-2/snapshots/petsc-current/docs/manualpages/DA/DARestoreGlobalVector.html#DARestoreGlobalVector

Perhaps I'm misunderstanding how Get/Restore are being used.  I'll let
one of the developers chime in on this when they've got a moment.

~A

On 1/27/07, Brian Grierson <bag2107 at columbia.edu> wrote:
> Another quick question.  PETSc online help says DAGetGlobal/DARestoreGlobal
> is a Seq vector operation, while
> DACreateGlobal/VecDesroy is parallel.
>
> I don't understand how you could create a global vector in a Seq manner on a
> DA???
>
>
>
> Brian A. Grierson
>
>
>
>
> Department of Applied Physics
>
> 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
>
>
> On Jan 27, 2007, at 6:41 PM, Aron Ahmadia wrote:
>
> 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
>
>
>
>
>
>
>
>
>
>
>
> Brian A. Grierson
>
>
>
>
> Department of Applied Physics
>
> 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
>
>
>
>