On Fri, Nov 20, 2009 at 2:57 PM, Michael Creel <michael.cr...@uab.es> wrote:
>
>
> On Fri, Nov 20, 2009 at 1:57 PM, Jaroslav Hajek <high...@gmail.com> wrote:
> >
> >
> > On Fri, Nov 20, 2009 at 1:44 PM, Michael Creel <michael.cr...@uab.es>
> wrote:
> >>
> >> Hi all,
> >>
> >> In another message, Jaroslav made the comment
> >>
> >>> 1. info is the first output argument in all functions. I think it
> should
> >>> be the second one, so that it can be easily ignored if wanted.
> >>> In particular, the check in examples
> >>>
> >>> if not(MPI_Initialized)
> >>> info = MPI_Init();
> >>> end
> >>>
> >>> makes no sense (unless I'm missing something) because it's the info
> >>> output from MPI_Initialized that is tested and that is always zero.
> >>
> >> This follows the MPI standard, which says:
> >>>
> >>> All MPI routines (except MPI_Wtime and MPI_Wtick) return an error
> value;
> >>> C routines as the value of the function and Fortran routines in the
> last
> >>> argument. Before the value is returned, the current MPI error handler
> is
> >>> called. By default, this error handler aborts the MPI job. The error
> handler
> >>> may be changed with MPI_Errhandler_set; the predefined error handler
> >>> MPI_ERRORS_RETURN may be used to cause error values to be returned.
> Note
> >>> that MPI does not guarentee that an MPI program can continue past an
> error.
> >>>
> >>> MPI_SUCCESS No error; MPI routine completed successfully.
> >>
> >> Following the standard is a big plus, in my opinion. That way, knowledge
> >> about MPI previously gained from C or Fortran will be useful when using
> MPI
> >> with Octave.
> >
> > Yes, my approach still follows the standard, it's just more convenient to
> > use. The standard says nothing about how external bindings should behave.
> >
>
> Right, but MPI functions for C or Fortran don't return anything but things
> like info, flag, status. The contents of messages passed back and forth are
> not obtained from return values of functions. It's certainly possible to
> place a received message into the output of a MPI_Recv binding, and there
> may be a some logic to the idea, but it is a step away from the C and
> Fortran way of doing things. Most people will learn about MPI though C and
> Fortan tutorials, so following that syntax is not a bad idea. What would you
> propose to use as outputs of functions?
>
> M.
>
I think you didn't understand, Michael. What I'm proposing is just to switch
the order to a more convenient one.
Take the simplest example: MPI_Initialized.
This is now called like
[info, flag] = MPI_Initialized ();
where info is always zero (MPI_SUCCESS) and flag is the actual result. What
I'm proposing is to use instead
[flag, info] = MPI_Initialized ();
because then the call
flag = MPI_Initialized (); # ignore info
is possible, and it is also possible to do
if (MPI_Initialized)
something
endif
In C, the corresponding call is
info = MPI_Initialized (&flag);
but there is *no* way you can preserve this structure in Octave. In Octave,
every output argument must be a return value; there is no other way (unless
you pass names and manipulate the caller scope directly).
--
RNDr. Jaroslav Hajek
computing expert & GNU Octave developer
Aeronautical Research and Test Institute (VZLU)
Prague, Czech Republic
url: www.highegg.matfyz.cz
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