[Research] 3 fast algorithms to compute "Combination" operation

Method 1  is faster 10 times than method 2

Method 1:

- Download package "gmpy2" from https://code.google.com/p/gmpy/

- Install with the corresponding Python (e.g, 2.7, 3.1,...)

import gmpy2

a = gmpy2.comb (5, 3)

--> The result is 10

Method 2

def choose(n, k):
    """
    A fast way to calculate binomial coefficients by Andrew Dalke (contrib).
    """
    if 0 <= k <= n:
        ntok = 1
        ktok = 1
        for t in xrange(1, min(k, n - k) + 1):
            ntok *= n
            ktok *= t
            n -= 1
        return ntok // ktok
    else:
        return 0

Method 3:

- Using scipy.misc.comb()