code: def LogBinomialCoef(n, k):
      
      return n * log(n) - k * log(k) - (n - k) * log(n - k)
docs: Computes the log of the binomial coefficient.
  
      http://math.stackexchange.com/questions/64716/
      approximating-the-logarithm-of-the-binomial-coefficient
  
      n: number of trials
      k: number of successes
  
      Returns: float