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

[Van Snyder]

The word "symmetric" appears exactly once in 09-007r2, in 9.5.4p1.

On Tue, 2009-07-28 at 17:08 -0700, Craig Dedo wrote:
> > -----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
> P. O. Box 423                  Mobile Phone:  (414) 412-5869
> Brookfield, WI   53008-0423    E-mail:  <craig at ctdedo.com>
> USA
> Linked-In:  http://www.linkedin.com/in/craigdedo
> 
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