[petsc-users] DM Vector get vs. create

[Richard Mills]

Barry,

Perhaps it would be good to put your explanation into the manual pages for
these routines?  The difference between the two is not obvious without
looking at examples.

--Richard

On Wed, May 6, 2015 at 3:32 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
> > On May 6, 2015, at 5:24 PM, Gideon Simpson <gideon.simpson at gmail.com>
> wrote:
> >
> > What are the relative merits of DMGetGlobalVector and
> DMCreateGlobalVector, and the analogous question for the Local Vectors?
> Are there scenarios where one should be used over the other?
>
>    Get are intended for obtaining work vectors that one intends to restore
> soon, likely in the same function that did the get. Create is for long
> living vectors that you are likely passing around to solvers, subroutines
> etc.
>
>     Explanation: sometimes a subroutine needs some work vectors. For
> example often a PETSc SNESFormFunction will do a DMGlobalToLocalBegin/End()
> at the beginning to allow access of ghost values. That local vector is only
> needed in that subroutine so one should use the get.
>
>
> >
> > -gideon
> >
>
>
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