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

[Robert Corbett]

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?

The idea is somewhat like the concept of a projection in geometry.
Perhaps PROJECTIVE?

Bob Corbett