(j3.2006) a question on cobounds

[Bill Long]

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.


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



> 
> =
> 
> 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
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