03-scatter-gather

#!/usr/bin/env python

from __future__ import division
from __future__ import print_function

import numpy as np
from mpi4py import MPI

from parutils import pprint

comm = MPI.COMM_WORLD

pprint("-"*78)
pprint(" Running on %d cores" % comm.size)
pprint("-"*78)

my_N = 4
N = my_N * comm.size

if comm.rank == 0:
    A = np.arange(N, dtype=np.float64)
else:
    A = np.empty(N, dtype=np.float64)

my_A = np.empty(my_N, dtype=np.float64)

# Scatter data into my_A arrays
comm.Scatter( [A, MPI.DOUBLE], [my_A, MPI.DOUBLE] )

pprint("After Scatter:")
for r in range(comm.size):
    if comm.rank == r:
        print("[%d] %s" % (comm.rank, my_A))
    comm.Barrier()

# Everybody is multiplying by 2
my_A *= 2

# Allgather data into A again
comm.Allgather( [my_A, MPI.DOUBLE], [A, MPI.DOUBLE] )

pprint("After Allgather:")
for r in range(comm.size):
    if comm.rank == r:
        print("[%d] %s" % (comm.rank, A))
    comm.Barrier()