Re: MPI

[Alex Verstak]

On Sat, 3 Feb 2001, John W. Eaton wrote:
> I took the time to look up the MPI standard, and here is what I found at
> http://www-unix.mcs.anl.gov/mpi/mpi-standard/mpi-report-2.0/node43.htm#Node43:

<snip argc=NULL, argv=NULL comment>

> So I don't think it matters whether you have the exact argv/argc that
> are passed to main.

MPI 2.0 is not widely supported yet.  The latest and the greatest
MPICH 1.2.1 crashes on MPI_Init(NULL, NULL).

> (BTW, I think there is a slight error in the
> standard, since an argc == NULL doesn't make sense.)

It's a pointer to argc.

> However, at http://www-unix.mcs.anl.gov/mpi/www/www3/MPI_Init.html I
> see that
> 
>   The MPI standard does not say what a program can do before an MPI_INIT
>   or after an MPI_FINALIZE. In the MPICH implementation, you should do
>   as little as possible. In particular, avoid anything that changes the
>   external state of the program, such as opening files, reading standard
>   input or writing to standard output.
> 
> But I suspect that this still doesn't mean that Octave must call
> MPI_Init before doing anything, or that it must be done in main(), or
> that it can't go in a .oct file, though you may need to call MPI_Init
> before doing any other operations in your program.

For that matter, MPI doesn't say that file i/o is available any
time, not just before MPI_Init.  Chances are, Octave won't run on
machines where it matters anyway. ;-)

Bottom line, I got the .oct file to work with MPICH on a
Linux/Myrinet cluster and with LAM on a cluster of workstations. 
No changes to Octave necessary.  I'll test it on a few other
configurations before releasing the source (may take a few weeks).

=alex



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