On Dec 15, 2011, at 9:09 AM, Joao Amaral wrote:
> Strangely(?), in both my laptop and the cluster, the number of threads from the command
> call MPI_Comm_size ( MPI_COMM_WORLD, p, error )
Did you really mean "threads" there?
Open MPI is process-parallel, meaning that calling COMM_SIZE on a communicator will return the number of *processes* in that communicator, not threads.
See the man page for mpirun(1) for how to launch multiple processes in a single MPI job. Quick example:
mpirun --hostfile your_host_file -np 8 your_mpi_program
your_host_file: a file listing the host names to launch on
8: number of copies of your_mpi_program to launch
your_mpi_program: your compiled executable MPI application
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