HPC FAQ - MPI

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Frequently Asked Questions

• 1. How do I compile an executable file to run as an MPI application?
• 2. Which compilers should I use to compile an MPI application?
• 3. How do I execute an MPI program on multiple cores?
• 4. Where can I get more MPI documentation?
• 5. How do I use multiple-level parallelism?

1. How do I compile an executable file to run as an MPI application?

To compile a source file named my_app written in C, use the command:

To compile a source file named myapp written in Fortran 90 use the command:

See the MPI Documentation section of this Web site for more information on MPI compiling.

Also, see man mpicc for C compiler specifics and man mpif90 for Fortran90 compiler specifics.

2. Which compilers should I use to compile an MPI application?

For applications in C use mpicc. For applications in Fortran 90 use mpif90.

3. How do I execute an MPI program on multiple nodes?

Create a shell script and submit it to the batch scheduler. For example, the script file myscript might look like this:

If you prefer a different shell, you can use sh, ksh, csh, or bash. We recommend bash, which is the default.

Run it with a command like sbatch -n t myscript, where t is the number of tasks. The batch scheduler will distribute the job over the required number of nodes.

4. Where can I get more MPI documentation?

See the MPI documentation in the Documentation section.

5. How do I use multiple-level parallelism?

To use multiple-level parallelism, which is running an MPI job that uses OpenMP, loop-parallelism, or that calls a parallelized library routine, consult the Multi Node Parallelism documentation.