normal function is 10x faster

I tested my normal function by comparing its output to that of norm.pdf

    from scipy.stats import norm
    import math

    def normal(x, sigma, mu=0.0):
        """
        See equation at http://en.wikipedia.org/wiki/Normal_distribution
        """
        power = -(x-mu)**2 / (2.0*sigma**2.0)
        multiple = (1.0 / (sigma * math.sqrt(2.0 * math.pi)))
        return multiple * math.e**power

    mu = 0.0
    sigma = 0.05
    x = 0
    norm.pdf(loc=mu, scale=sigma, x=x)
    7.9788456080286538
    normal(x,sigma,mu=mu)
    7.978845608028654