--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/ch5ex3.py	Sun Jan 06 18:11:17 2013 -0600
@@ -0,0 +1,50 @@
+"""Chapter 5.3 exercise 3 in Allen Downey's Think Complexity book.
+
+"Write a function called plot_ccdf that takes a list of values and the
+corresponding list of probabilities and plots the CCDF on a log-y scale.
+
+To test your function, use expovariate from the random module to generate 100
+values from an exponential distribution. Plot the CCDF on a log-y scale and see
+if it falls on a straight line."
+
+"""
+import random
+import sys
+
+import matplotlib.pyplot as pyplot
+
+
+def plot_ccdf(x_vals, y_vals, title=''):
+    """Given a set of x-values and y-values from a continuous distribution, plot
+    the complementary distribution (CCDF) on a log-y scale.
+
+    """
+    if len(x_vals) != len(y_vals):
+        raise ValueError
+
+    ys = [1.0 - y for y in y_vals]
+
+    pyplot.clf()
+    pyplot.xscale('linear')
+    pyplot.yscale('log')
+    pyplot.title(title)
+    pyplot.xlabel('x')
+    pyplot.ylabel('1-y')
+    pyplot.plot(x_vals, ys, label='1-y', color='green', linewidth=3)
+    pyplot.legend(loc='upper right')
+    pyplot.show()
+
+
+def main(script, lambd):
+
+    lambd = float(lambd)
+
+    x_vals = range(100)
+    y_vals = [random.expovariate(lambd) for x in x_vals]
+    y_vals.sort()
+
+    plot_ccdf(x_vals, y_vals, 'expovariate w/lambda = {}'.format(lambd))
+
+
+if __name__ == '__main__':
+    main(*sys.argv)