jbornschein / Mpi4py Examples

=== Dependencies ===

These programs depend on mpi4py (>= Version 1.0)

The mpi4py documentation and installation instructions can be found at:

http://mpi4py.scipy.org/

=== How to run on a single (multi-core) host ===

Run it with

mpirun -np 4 ./some-program

where the number after "-np " is the number of parallel MPI processes to be started.

=== How to run on multiple hosts ===

If you want to run the program distributed over multiple hosts, you have to create a which looks like:

-- hostfile -- host1 slots=4 host2 slots=4 host3 slots=4

Where "slots=" specifies the number of parallel processes that should be started on that host.

Run it with

mpirun --hostfile ./some-program

=== Run on a cluster with the Torque Job scheduling system ===

There are two possibilities:

a) Run interactively:

Request an interactive session and allocate a number of processors/nodes for your session:

$ qsub -I X -l nodes=4:ppn=4

Where "-I" means you want to work interactively, "-X" requests grapical (X-Window) I/O -- (you can run arbitrary programs that open windows). The option "-l " specifies the resources you want to allocate. "-l nodes=4:ppn=4" requests four compute nodes with each having four processor cores [ppn =^ ProcessorsPerNode]. So in total you allocate 16 CPU cores. [The scheduler is free to run your job on two nodes having 8 CPU cores each]

Once your interactive session is ready, you run

$ mpirun ./your-program

mpirun automatically knowns how many parallel processes have to be started and where they have to be started.

b) Submit as non-interactive batch-job:

Use

$ qsub -l nodes=4:ppn=4 ./your-jobfile.job

to submit jour job-file. Similar to the interactive case, "-l" again is used
to request resources from the scheduling system. The job file usually is a simple shell script which specifies the commands to be run once your job starts. In addition, the jobfile can contain "#PBS " statements which are used to specify additional options which could have been specified in the "qsub" commandline. Please see "man qsub" for details.