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Subject: Re: [OMPI users] Fortran - MPI_WORLD_COMM - correction
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2010-06-22 19:04:18

On Jun 22, 2010, at 6:46 PM, Mihaly Mezei wrote:

> I just tried adding the include statement, but this is what I got:
> % mpif90 -o mpi0 mpi0.f
> /share/apps/openmpi-1.4.1/include/mpif-common.h(402): error #6406: Conflicting attributes or multiple declaration of name. [MPI_COMM_WORLD]
> parameter (MPI_COMM_WORLD=0)
> -----------------^
> compilation aborted for mpi0.f (code 1)

I'm guessing you didn't rename the parameter of the function (in your original source code, you had named a parameter MPI_COMM_WORLD). That would cause a conflict. In general, it's a Bad Item to name parameters -- or any symbols, really -- with an MPI_* prefix. The MPI_* prefix is reserved for the MPI library.

So you actually had a few problems:

- naming a parameter MPI_COMM_WORLD (causing a conflict when including mpif.h)
- not including mpif.h in the subroutine (resulting in MPI_INTEGER having an undefined value)
- you passed a MPI_COMM_WORLD in both a common block (through an intermediate integer) and as a parameter; I'm guessing that was just iterating through your testing, but just to be clear -- you only need one or the other, not both (or just including "mpif.h" if you know you're going to use MPI_COMM_WORLD)

FWIW, I'd strongly recommend using "IMPLICIT NONE" in your code to prevent accidental use of variables without defined values, etc.

Jeff Squyres
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