RE: [Freepooma-devel] [PATCH] Canonicalize handling ofexternal/internal guards

[Julian C. Cummings]

Hi,

Sorry for coming late to this discussion.  I don't really participate in the
POOMA developments anymore, but thought I should pipe up regarding this
issue of particle gather/scatter methods and guard layers.  I just wanted to
point out that the behavior of eliminating internal guard layers when there
is only one Field patch is correct.  The internal guard layers are meant
only to provide consistency across processor (or virtual node) boundaries.
If there will be no such boundaries (i.e., only one Field patch), then there
is no need for any internal guard layers.  The code there was probably added
to prevent any "naïve user" behavior. ;-)  However, there are also external
guard layers intended to enforce physical domain boundary conditions.  The
user remains free to add these and select their BCs.  The coding error, IMO,
was with the InterpolatorCIC requiring that the number of *internal* guard
layers be greater than zero.  This logic should have been modified to allow
for the case where the number of internal guard layers is zero, but there is
only one Field patch and it has an external guard layer.  This is sort of a
corner case for POOMA, which is normally dealing with parallel computations
on decomposed Fields; nevertheless, it should be allowed by the
Interpolators that require a guard layer.  I hope these comments make sense
to you.  I did not examine the patch you proposed, but from your description
it sounded like you were removing the optimization of deleting unneeded
internal guard layers.  That's not a good idea, IMO.  Maybe I have
misunderstood your comments in this e-mail exchange.  I don't have the time
to follow the POOMA developments very closely these days, so take my
comments in that context.

Regards, Julian C.

Dr. Julian C. Cummings
Staff Scientist, CACR/Caltech
(626) 395-2543
address@hidden
  

> -----Original Message-----
> From: 
> address@hidden 
> [mailto:address@hidden
rg] On Behalf Of Richard Guenther
> Sent: Monday, April 11, 2005 3:20 AM
> To: address@hidden
> Subject: Re: [Freepooma-devel] [PATCH] Canonicalize handling 
> ofexternal/internal guards
> 
> On Fri, 1 Apr 2005, Richard Guenther wrote:
> 
> > Hi!
> >
> > This patch canonicalizes the handling of hasInternalGuards_m and 
> > hasExternalGuards_m in the various grid layouts.  It also disables 
> > optimizing away of internal guards if the partitioner will 
> create at 
> > most one patch.
> 
> I believe that the current way of doing things is correct 
> (apart from not all places being consistent), i.e. have 
> hasInternalGuards and guards() being consistent.  What the 
> Interpolators really are asking from the Layouts is the 
> maximum supported stencil size, a thing the layouts cannot 
> answer atm.  For this we need to provide functionality.
> 
> I'll update the patch to canonicalize all this handling and 
> apply it to HEAD, maybe to r2_branch, too.
> 
> Richard.
> 
> 
> 
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