about ghosted vectors and there local representation

Matthew Knepley knepley at gmail.com
Tue Jun 20 09:24:57 CDT 2006

In the DA we have some idea of topology, so we can make a sensible
reordered local vector. The VecGhost is a lower level construct. All it
does is maintain a vector of this form

   [ local values | ghost values ]

The update maps from local values to ghost values with a scatter. The
VecGhostGetLocalForm() just pulls out the pointer. We could add code
which maps into a different local vector using an ordering, but this can
already be done with an AO as well.


On 6/20/06, Thomas Geenen <geenen at gmail.com> wrote:
> On Tuesday 20 June 2006 13:32, you wrote:
> > > I now expect the vector to be in the local form. That means that the
> > > positions
> > > that I created as ghost points are filled with the solution
> corresponding
> > > to
> > > the global solution. I expect that they are inserted in the position
> in
> > > my local vector corresponding to there corresponding global position.
> >
> > Not sure what you mean here.  The local form is the same as the global
> > vector
> > in the owned spots, and then has the ghost points at the end.
> oke so that means (4,5,3) ??
> So if I need the solution in the same positions as the ones that i filled
> with
> VecSetValuesLocal I will have to reorder the vector
> What does VecGhostGetLocalForm do? inserts the global solution in the
> ghost
> points at the end? I thought  VecGhostUpdateBegin VecGhostUpdateEnd did
> that.
> thomas
> >     Matt

"Failure has a thousand explanations. Success doesn't need one" -- Sir Alec
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