I'm learning how to use MPI, and am confused on the difference between -n and -np when calling a script. For reference, I am trying to run the script on a Slurm cluster with OpenMPI 3.
For instance, I can run my script like this:
mpirun -n 4 --oversubscribe python par_PyScript2.pyor like this:
mpirun -np 4 --oversubscribe python par_PyScript2.pyCan someone describe what these options actually mean?
Best Answer
The manual says that -n and -np are synonyms. And so are -c and --n. They instruct mpirun to
Run this many copies of the program on the given nodes.
So it basically is the number of MPI ranks you want. Note that in a Slurm context, you should not specify it explicitly; the information is passed from Slurm to OpenMPI.
Use the manual
man mpirunSearch for that by typing /-n and to go to next match, press n.
From the online manual, I see no option -n. Though, it is possible that -n is just an alias for -np