add calculate pi demo

demos/calculate_pi/calculate_pi.py

@@ -0,0 +1,44 @@
+#!/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 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 = 10000000
+    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)

demos/calculate_pi/slurm_submit_calculate_pi.sh

@@ -0,0 +1,10 @@
+#!/bin/bash
+#SBATCH --ntasks=6
+
+# Requires python3, a configured MPI environment
+# and the Python packages mpi4py and numpy to be
+# available in PATH.
+
+cd $SLURM_SUBMIT_DIR
+
+mpiexec -n 6 python3 ./calculate_pi.py