Updating the monte carlo pi example

- It now has benchmarks and a host version

Author: pavanky

examples/monte_carlo_pi.py

@@ -1,13 +1,41 @@
 #!/usr/bin/python
+from random import random
+from time import time
 from arrayfire import (array, randu)
 import arrayfire as af
-import random
+
+#alias range / xrange because xrange is faster than range in python2
+try:
+    frange = xrange  #Python2
+except NameError:
+    frange = range   #Python3
+
 
 def calc_pi_device(samples):
     x = randu(samples)
     y = randu(samples)
     return 4 * af.sum((x * x  + y * y) < 1) / samples
 
+# Having the function outside is faster than the lambda inside
+def in_circle(x, y):
+    return (x*x + y*y) < 1
+
+def calc_pi_host(samples):
+    count = sum(1 for k in frange(samples) if in_circle(random(), random()))
+    return 4 * float(count) / samples
+
+def bench(calc_pi, samples=1000000, iters=25):
+    func_name = calc_pi.__name__[8:]
+    print("Monte carlo estimate of pi on %s with %d million samples: %f" % \
+          (func_name, samples/1e6, calc_pi(samples)))
+
+    start = time()
+    for k in frange(iters):
+        calc_pi(samples)
+    end = time()
+
+    print("Average time taken: %f ms" % (1000 * (end - start) / iters))
+
 if __name__ == "__main__":
-    samples=1000000
-    print("Monte carlo estimate of pi with %d samples: %f" % (samples, calc_pi_device(samples)))
+    bench(calc_pi_device)
+    bench(calc_pi_host)