[petsc-dev] VecScatter

[Dmitry Karpeev]

On Tue, Jan 4, 2011 at 4:30 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
> On Jan 4, 2011, at 3:45 PM, Dmitry Karpeev wrote:
>
> > VecScatter, at least the PtoP and PtoS versions, computes what amounts to
> a "localToGlobal" map, which is used
> > to set up the communication datastructures, but is later discarded.  This
> information appears, for example,
> > as the the inidx and inidy index array pair that VecScatterCreate_PtoP
> passes to VecScatterCreate_PtoS
> > and later frees.  It would be very useful to retain this information for
> my work on FETI-adapted matrices.
> > Would it be okay if I stashed this info in _p_VecScatter?
> >
>   Fine, whatever. What about saving it only if some option is set, so we
> don't waste the memory otherwise?
>
I'll do that.
Dmitry.

>
>   Barry
>
> > I realize that this cuts a bit too close to PETSc's critical
> functionality, but it seems to me that this is only
> > minimally intrusive. The alternative would be to reconstruct this
> information from VecScatter's to/from->indices,
> > but these are (re)arranged by the receiving proc and searching through
> those isn't as convenient.  Of course,
> > for the special case scatters (SStoSG, MPItoAll, etc) the reconstruction
> has to take place in any event,
> > but I thought it would be useful to avoid it where the equivalent info is
> already computed as part of the
> > scatter's constructor.
> >
> > Any thoughts/objections?
> >
> > Dmitry.
>
>
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