(j3.2006) (SC22WG5.5141) [ukfortran] image selectors

[Van Snyder]

On Tue, 2013-12-10 at 09:23 +0000, N.M. Maclaren wrote:
> On Dec 10 2013, Tom Clune wrote:
> >On Dec 9, 2013, at 6:52 PM, Van Snyder <Van.Snyder at jpl.nasa.gov> wrote:
> >
> >> Better yet would be to specify the mapping from parent team to subteam.
> >> If NEW_INDEX is not specified, is there really a difficulty with
> >> specifying, for example, that the image indices for the subteam are in
> >> the same order as the image indices in the parent team, so that image
> >> index 1 for the subteam applies to the image with the smallest image
> >> index in the parent team that becomes part of the subteam, etc.?
> >
> > I'll second that. ince many applications will be ported from MPI, the 
> > principle of "least surprise" should be invoked here. Unless there is a 
> > reason to the contrary, the MPI convention for subcommunicator ranks 
> > should apply to subteam image indices. MPI allows redefining ranks as 
> > well, but I've only used that once (maybe) in 20+ years of coding in MPI.
> 
> Yes, but I do NOT agree with that specification!  It should simply be
> explicitly stated to be unspecified, thus permitting an implementation
> to optimise.  Few will, but so what?

It is explicitly stated to be unspecified, but not using the term
"processor dependent."

I don't see how there are opportunities for optimization by not
specifying the mapping from parent team cosubscripts to subteam
subscripts.

> 
> 
> Regards,
> Nick Maclaren.
> 
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