(j3.2006) a question on cobounds

[Bill Long]

Jim Xia wrote:
> 

> 
>  > I'm guessing you have not written code that uses coarrays to represent a
>  > distributed array across a 2- or 3-dimensional grid. Coarrays with
>  > corank > 1 are enormously useful for program clarity and maintainability
>  >   in cases like this, and this is a pretty common case. This is a big
>  > advantage we have over UPC and MPI.  There are others as well, of course.
> 
> 
> No, I haven't written any real coarray programs -- where do I obtain a 
> compiler for it?  I bought the original argument for supporting higher 
> corank just for these reasons.  Now the fact that you can have 
> adjustable cobounds starts to reverse my view on this support.  I cannot 
> enthusiastically tell anyone that coarrays are a good thing to use, at 
> least not this part of the feature.
> 


I believe there are potential uses for this feature. For example:

    real,save :: u[-N:*]

would allow you to reference the values to the "left" and "right" of 
image N simply as u[-1] and u[1].

The main reason for allowing this flexibility was not having a good 
reason to disallow it. Certainly there is no implementation issue.  Many 
recent changes in Fortran have been argued on the basis of a restriction 
being unnecessary.  Retaining this flexibility is not central to the 
usability of coarrays.  I propose we discuss the pros and cons and then 
have a straw vote on the question at the August meeting.

Cheers,
Bill


> 
> Cheers,
> 
> 
> Jim Xia
> 
> XL Fortran Compiler Test
> IBM Toronto Lab at 8200 Warden Ave, Markham, On, L6G 1C7
> Phone (905) 413-3444  Tie-line 313-3444
> email: jimxia at ca.ibm.com
> D2/YF7/8200 /MKM
> 
> http://www.ibm.com/software/awdtools/fortran/xlfortran
> 
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-- 
Bill Long                                   longb at cray.com
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