Birthday Paradox

gistfile1.py

%pylab inline --no-import-all
import matplotlib.pyplot as plt

def prob_samebirthday(n):
    prob_days = [ (1.0-(i/365.0)) for i in xrange(1,n+1) ]
    return 100.0*(1.0-reduce(lambda x,y: x*y, prob_days))

def draw():
    plt.figure()
    plt.grid(True)
    plt.xlabel("people")
    plt.ylabel("probability")
    plt.title("Birthday Paradox")
    y = []
    x = xrange(1,101)
    y = [ prob_not_sameday(i) for i in x ]
    plt.plot(x, y, 'r', linewidth=3)
    plt.plot([21, 21], [0, y[21]], color='blue', linestyle='--', linewidth=2)
    plt.plot([0, 21], [y[21], y[21]], color='blue', linestyle='--', linewidth=2)
    show()

draw()