#--------------
# Loaded Modules
#--------------
import numpy as np
from mpi4py import MPI
 
#-------------
# Communicator
#-------------
comm = MPI.COMM_WORLD
 
my_N = 4
N = my_N * comm.size
 
if comm.rank == 0:
    A = np.arange(N, dtype=np.float64)
else:
    #Note that if I am not the root processor A is an empty array
    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] )
 
if comm.rank == 0:
   print "After Scatter:"
 
for r in xrange(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] )
 
if comm.rank == 0:
   print "After Allgather:"
 
for r in xrange(comm.size):
    if comm.rank == r:
        print "[%d] %s" % (comm.rank, A)
    comm.Barrier()