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Subject: Re: [OMPI users] OpenMPI runtime-specific environment variable?
From: Jed Brown (jed_at_[hidden])
Date: 2008-10-22 04:30:46

On Wed 2008-10-22 00:40, Reuti wrote:
> Okay, now I see. Why not just call MPI_Comm_size(MPI_COMM_WORLD,
> &nprocs) When nprocs is 1, it's a serial run. It can also be executed
> when not running within mpirun AFAICS.

This is absolutely NOT okay. You cannot call any MPI functions before
MPI_Init (and at least OMPI 1.2+ and MPICH2 1.1a will throw an error if
you try).

I'm slightly confused about the original problem. Is the program linked
against an MPI when running in serial? You have to recompile anyway if
you change MPI implementation, so if it's not linked against a real MPI
then you know at compile time. But what is the problem with calling
MPI_Init for a serial job? All implementations I've used allow you to
call MPI_Init when the program is run as ./foo (no mpirun).


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