# 4.10. MPI Applications¶

CUs which execute MPI applications are, from an RP application perspective, not really different from other CUs – but the application needs to communicate to RP that the unit will (a) allocate a number of cores, and (b) needs to be started under an MPI regime. The respective CU description entries are shown below:

cud = rp.ComputeUnitDescription()

cud.executable  = '/bin/echo'
cud.arguments   = ['-n', '\$RP_UNIT_ID ']
cud.cores       = 2
cud.mpi         = True


This example should result in the unit ID echo’ed twice, once per MPI rank.

## 4.10.1. Running the Example¶

09_mpi_units.py. uses the above blob to run a bag of duplicated echo commands:

## 4.10.2. What’s Next?¶

Running MPI applications, and :ref:providing more generic environment setup <chapter_user_guide_10>`, are the topics for the next two sections.