(j3.2006) Alternatives for SYMMETRIC (Was: a question on cobounds)

[Craig Dedo]

> -----Original Message-----
> From: j3-bounces at j3-fortran.org [mailto:j3-bounces at j3-fortran.org] On
> Behalf Of Bill Long
> Sent: Tuesday, July 28, 2009 13:00
> To: Loren P Meissner
> Cc: 'fortran standards email list for J3'
> Subject: Re: (j3.2006) a question on cobounds
> 
> Loren P Meissner wrote:
> > Can somebody come up with a better term than SYMMETRIC for this
> concept?
> > (Unless the term is already imbedded in the standard.) Do you mean
> > something like "the array size is invariant across images"?
> 
> The term "symmetric" appears only once in the standard, in reference to
> files and units.
> 
> > I always thought a "symmetric array" is supposed to be one where A(I,
> J)
> > and A(J, I) have the same VALUE for all I and J.
> An obvious potential source of confusion, especially if the reader has
> a
> background in mathematics.
> 
> This terminology is
> > obviously not intended here, so it needs to at least be explained
> away
> > if people continue to use it.

	FWIW, I had the same confusion that Loren did.
 
> The use of "symmetric" is historical, dating back to the SHMEM library,
> where memory was allocated on a "symmetric heap", with the property
> that
> the allocated space had the same base address on every processor.  The
> symmetry is in the location of the data, not its values. Coarrays
> evolved out of this model and the terminology has stuck.  The standard
> does not mandate that coarrays be stored at "symmetric" memory
> addresses, though there are obvious advantages for a distributed memory
> implementation to do that.
> 
> Cheers,
> Bill

	Thanks for the explanation of the origin of this use of "SYMMETRIC",
Bill.  Unfortunately, like a lot of terms that software developers use, this
use of the word in this context is confusing and misleading.  

	I firmly believe in straightforward terminology.  We should
diligently search for a better term for this concept.  Here are a few
suggestions.  Perhaps someone else will come up with a better term.

	COMPATIBLE - the coarrays are compatible with each other on all
images.

	CONSISTENT - the coarrays are consistent with each other on all
images.

Anyone have any better ideas?

> >
> > LOREN
> >
> > -----Original Message-----
> > From: j3-bounces at j3-fortran.org [mailto:j3-bounces at j3-fortran.org] On
> > Behalf Of Bill Long
> > Sent: Tuesday, July 28, 2009 9:23 AM
> > To: fortran standards email list for J3
> > Subject: Re: (j3.2006) a question on cobounds
> > [...]
> >
> > 2) Having the cobounds the same on all images enhances the concept
> that
> > THE ARRAYS ARE SYMMETRIC ACROSS IMAGES.
> >
> 
> --
> Bill Long                                   longb at cray.com
> Fortran Technical Support    &              voice: 651-605-9024
> Bioinformatics Software Development         fax:   651-605-9142
> Cray Inc., 1340 Mendota Heights Rd., Mendota Heights, MN, 55120
> 

Sincerely,
Craig T. Dedo
17130 W. Burleigh Place
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