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Compute Pi using Python and MPI4PY
"""
This code computes pi. It's not the first python
pi computation tool that I've written. This program
is a good test of the mpi4py library, which is
essentially a python wrapper to the C MPI library.
To execute this code:
mpiexec -np NUMBER_OF_PROCESSES -f NODES_FILE python mpipypi.py
where....
NUMBER_OF_PROCESSES is the number of desired processes.
NODES_FILE is a file which records the location of your nodes.
"""
from mpi4py import MPI
comm = MPI.COMM_WORLD
rank = comm.Get_rank()
size = comm.Get_size()
slice_size = 1000000
total_slices = 50
# This is the master node.
if rank == 0:
pi = 0
slice = 0
process = 1
print size
# Send the first batch of processes to the nodes.
while process < size and slice < total_slices:
comm.send(slice, dest=process, tag=1)
print "Sending slice",slice,"to process",process
slice += 1
process += 1
# Wait for the data to come back
received_processes = 0
while received_processes < total_slices:
pi += comm.recv(source=MPI.ANY_SOURCE, tag=1)
process = comm.recv(source=MPI.ANY_SOURCE, tag=2)
print "Recieved data from process", process
received_processes += 1
if slice < total_slices:
comm.send(slice, dest=process, tag=1)
print "Sending slice",slice,"to process",process
slice += 1
# Send the shutdown signal
for process in range(1,size):
comm.send(-1, dest=process, tag=1)
print "Pi is ", 4.0 * pi
# These are the slave nodes, where rank > 0. They do the real work
else:
while True:
start = comm.recv(source=0, tag=1)
if start == -1: break
i = 0
slice_value = 0
while i < slice_size:
if i%2 == 0:
slice_value += 1.0 / (2*(start*slice_size+i)+1)
else:
slice_value -= 1.0 / (2*(start*slice_size+i)+1)
i += 1
comm.send(slice_value, dest=0, tag=1)
comm.send(rank, dest=0, tag=2)
@rapsad

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rapsad commented May 8, 2016

Hello,
I would like to ask what type of algorithm are you using in this implementation of PI calculus.

@jcwright77

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jcwright77 commented Feb 23, 2017

This program sums the series for pi/4=arctan x |x=1 , in parallel by partitioning the domain across processors.

@mednadjib

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mednadjib commented Sep 19, 2019

@calcpage

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calcpage commented Dec 10, 2019

Well that is arctan(1) using a maclaurin expansion!

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