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from __future__ import print_function
from mpi4py import MPI
import numpy
from sys import stdout
comm = MPI.COMM_WORLD
myid = comm.Get_rank()
ntasks = comm.Get_size()
# Send and receive buffers
n = 10000000
data = numpy.zeros(n, int) + myid
buff = numpy.zeros(n, int)
# Message chain using Send and Recv
# Start measuring the time spent in communication
comm.barrier()
t0 = MPI.Wtime()
tgt = myid + 1
src = myid - 1
if myid < ntasks - 1:
comm.Send(data, dest=tgt, tag=tgt)
print(" Rank {0:d}: sent {1:d} elements to rank {2:d}.".format(myid,
len(data),
tgt))
if myid > 0:
comm.Recv(buff, source=src, tag=myid)
print(" Rank {0:d}: received an array filled with {1:d}s.".format(myid,
buff[0]))
t1 = MPI.Wtime()
# ... wait for every rank to finish ...
stdout.flush()
comm.barrier()
if myid == 0:
print("")
print("Timings")
print("Time elapsed in rank {0} {1:6.3f}".format(myid, t1 - t0))
stdout.flush()
comm.barrier()
if myid == ntasks - 1:
print("Time elapsed in rank {0} {1:6.3f}".format(myid, t1 - t0))