Re: Co-Array Fortran

On Oct 30, 8:48 pm, Walter Spector <w6ws_xthiso...@xxxxxxxxxxxxx>
wrote:
gary.l.sc...@xxxxxxxx wrote:
...
from walter spector

"a(i) = b(i) + c(i)[np]

The A and B references are local. But C is a coarray, and so would
load values from coarray process 'np'. (Which may or may not be local
-
depending on the value of np.) "

the last sentence seems to imply that with a [np] reference present,
it could denote either a local or remote reference depending on the
value. that superficially seem to conflict.

We are saying the same thing.

Upon startup, there are some fixed number of 'images' of the program
executing simultaneously. Each image has a complete (co)array C. C is not
'distributed'. If C is 100 elements long, it is 100 elements long on
EACH of the images. In this sense coarrays are like MPI programming.
Each image has its own version of the array.

So if, say, some image wants data from coarray C on image #10, it
would execute:

a(i) = b(i) + c(i)[10]

If, per chance, image #10 executed the above statement, the communication
would be to its own version of coarray C. Otherwise, the communication
would be a remote version of C (on image #10.)

Does that make sense?

Sure, I'm just not sure there aren't problems where it would be
critical to know whether the referenced array is a local one or a
remote one. It seems like there needs to be an inquiry routine to
tell whether it is local or remote and maybe in rare cases, copy local
for performance reasons or some other reason. Anyway, it isn't that
important that I understand since it's unlikely I'll ever use it.


Walt


.

Relevant Pages

  • Re: Co-Array Fortran
    ... For addressing "remote" data, you use the coarray notation (square ... for the actual communication mechanism. ... areas on a shared memory machine, a get/put on a distributed memory ...
    (comp.lang.fortran)
  • Re: Co-Array Fortran
    ... That could impact how you structure the problem solution. ... And that is the whole point of the coarray notation. ... For addressing "remote" data, you use the coarray notation (square ...
    (comp.lang.fortran)
  • Re: Co-Array Fortran
    ... load values from coarray process 'np'. ... the last sentence seems to imply that with a reference present, ... executing simultaneously. ... If, per chance, image #10 executed the above statement, the communication ...
    (comp.lang.fortran)