Hello world¶

This example talks about basics of rank and number of processes in MPI.

from mpi4py import MPI
comm = MPI.COMM_WORLD
rank = comm.Get_rank()
print('My rank is ',rank)

The following output is expected. (Assuming the --ntasks-per-node was assigned as 4.)

My rank is 2
My rank is 3
My rank is 1
My rank is 0

The variable comm holds the group of processes that can commmunicate with each other, with the default being MPI.COMM_WORLD. The rank variable on the other hand represents the particular process within the communicator. Indicating that the processors within ntasks-per-node can be assigned chunks of code separately, to perform parallel calculations.

This is explored in further sections.