How to run a python code with mpirun

To test this example start a job with 2 nodes, see Fig. 1

Fig. 1.

Note: Carme uses carme_mpirun instead of mpirun. The former adds additional flags to the mpirun command.

1. Open a terminal and install mpi4py.

    python -m pip install mpi4py
   

2. As an example, create a python file:

   cd /home/<username> && touch hello_world.py
   

3. Copy the following code to the file:

   #!/usr/bin/env python
   """
   Parallel Hello World
   """
   
   from mpi4py import MPI
   import sys
   
   size = MPI.COMM_WORLD.Get_size()
   rank = MPI.COMM_WORLD.Get_rank()
   name = MPI.Get_processor_name()
   
   sys.stdout.write(
      "Hello, World! I am process %d of %d on %s.\n"
      % (rank, size, name))
   

4. Run the file

    carme_mpirun -np 2 python hello_world.py
   

5. The output shows your two nodes:

   Hello, World! I am process 1 of 2 on fhgc2.
   Hello, World! I am process 0 of 2 on fhgc1.