import numpy

from mpi4py import MPI

import time

​

comm = MPI.COMM_WORLD

rank = comm.Get_rank()

size = comm.Get_size()

​

a = 1

b = 10000000

​

num_per_rank = b // size # the floor division // rounds the result down to the nearest whole number.

summ = numpy.zeros(1)

​

temp = 0

lower_bound = a + rank * num_per_rank

upper_bound = a + (rank + 1) * num_per_rank

print("This is processor ", rank, "and I am summing numbers from", lower_bound," to ", upper_bound - 1, flush=True)

​

comm.Barrier()

start_time = time.time()

​

for i in range(lower_bound, upper_bound):

    temp = temp + i

​

summ[0] = temp

​

if rank == 0:

    total = numpy.zeros(1)

else:

    total = None

​

comm.Barrier()

# collect the partial results and add to the total sum

comm.Reduce(summ, total, op=MPI.SUM, root=0)

​

stop_time = time.time()

​

if rank == 0:

    # add the rest numbers to 1 000 000

    for i in range(a + (size) * num_per_rank, b + 1):

        total[0] = total[0] + i

    print("The sum of numbers from 1 to 1 000 000: ", int(total[0]))

    print("time spent with ", size, " threads in milliseconds")

    print("-----", int((time.time() - start_time) * 1000), "-----")