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#!/usr/bin/env python
"""
Parallel PI computation using Collective Communication Operations (CCO)
within Python objects exposing memory buffers (requires NumPy).
usage::
$ mpiexec -n <nprocs> python cpi-buf.py
"""
from mpi4py import MPI
from math import pi as PI
from numpy import array
def get_n():
prompt = "Enter the number of intervals: (0 quits) "
try:
n = int(input(prompt))
if n < 0: n = 0
except:
n = 0
return n
def comp_pi(n, myrank=0, nprocs=1):
h = 1.0 / n
s = 0.0
for i in range(myrank + 1, n + 1, nprocs):
x = h * (i - 0.5)
s += 4.0 / (1.0 + x**2)
return s * h
def prn_pi(pi, PI):
message = "pi is approximately %.16f, error is %.16f"
print (message % (pi, abs(pi - PI)))
comm = MPI.COMM_WORLD
nprocs = comm.Get_size()
myrank = comm.Get_rank()
n = array(0, dtype=int)
pi = array(0, dtype=float)
mypi = array(0, dtype=float)
while True:
if myrank == 0:
_n = get_n()
n.fill(_n)
comm.Bcast([n, MPI.INT], root=0)
if n == 0:
break
_mypi = comp_pi(n, myrank, nprocs)
mypi.fill(_mypi)
comm.Reduce([mypi, MPI.DOUBLE], [pi, MPI.DOUBLE],
op=MPI.SUM, root=0)
if myrank == 0:
prn_pi(pi, PI)
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