import math


def normpdf(x, mean, sd):
    """
    Normal Probability Distribution Function

    return the probability based on a normal distribution
    guassian curve, given the x value, mean, and standard deviation.
    """
    #this because i can't get scipy to install
    var = float(sd)**2
    pi = 3.1415926
    denom = (2*pi*var)**.5
    num = math.exp(-(float(x)-float(mean))**2/(2*var))
    return num/denom