Update of cpi-cco.py from mpi4py to allow parameterisation of the iteration count at the command line, and to remove looping.

cpi-cco.py

#!/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
import argparse

parser = argparse.ArgumentParser()
parser.add_argument('iterations', metavar='N', type=int, nargs='?')
args = parser.parse_args()

def get_n():

    if args.iterations:
        return args.iterations
    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)

if myrank == 0:
    _n = get_n()
    n.fill(_n)
comm.Bcast([n, MPI.INT], root=0)

_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)


# =======================
# LICENSE: MPI for Python
# =======================
# 
# :Author:  Lisandro Dalcin
# :Contact: dalcinl@gmail.com
# 
# 
# Copyright (c) 2014, Lisandro Dalcin.
# All rights reserved.
# 
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
# 
# * Redistributions of source code must retain the above copyright
#   notice, this list of conditions and the following disclaimer.
# 
# * Redistributions in binary form must reproduce the above copyright
#   notice, this list of conditions and the following disclaimer in the
#   documentation and/or other materials provided with the distribution.
# 
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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