[Coarray-ts] Collectives

Bill Long longb at cray.com
Thu May 31 08:45:12 EDT 2012

The existing specific proposal for the collectives includes an optional 
"team" argument (assuming we do that form of teams).  If present, the 
operation is on the members of the team. If absent, all of the images 
are used.  If we adopt the partitioning scheme, then the set of images 
would not extend outside the current partition.   I think "set of 
images" covers these cases.


On 5/30/12 9:46 PM, Malcolm Cohen wrote:
> Now, I want to talk about teams and collectives.  Do these mix?  If a
> member of a team calls a collective, is it the whole world that
> participates or just the team?  I would have thought, perhaps wrongly,
> that collectives that operate over the whole image space only are of
> limited use (it certainly rules them out for any library routine, since
> the synchronisation is over the whole image space). So I would have
> thought that even if we did not have teams, we would want team-like
> collectives.  If we do have teams, then the team mechanism would be the
> obvious one for selecting the participating images.
> So in fact what *I* would expect a collective subroutine to do would be
> to perform a computation based on the value of a coarray on a set of
> images, not all images.  And the result of that computation would be
> made available on one or more of the participating images.  Should that
> be a set of the participating images, or limited to being one or all of
> them?  Just one or all is probably good enough I would guess.

Bill Long                                           longb at cray.com
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