get an x and y numpy.ndarray that spans the +/- 4
    standard deviation range of a gaussian distribution with
    a given mean and standard deviation. useful for plotting

    Parameters
    ----------
    mean : float
        the mean of the distribution
    stdev : float
        the standard deviation of the distribution
    num_pts : int
        the number of points in the returned ndarrays.
        Default is 50

    Returns
    -------
    x : numpy.ndarray
        the x-values of the distribution
    y : numpy.ndarray
        the y-values of the distribution

def gaussian_distribution(mean, stdev, num_pts=50):
    """ get an x and y numpy.ndarray that spans the +/- 4
    standard deviation range of a gaussian distribution with
    a given mean and standard deviation. useful for plotting

    Parameters
    ----------
    mean : float
        the mean of the distribution
    stdev : float
        the standard deviation of the distribution
    num_pts : int
        the number of points in the returned ndarrays.
        Default is 50

    Returns
    -------
    x : numpy.ndarray
        the x-values of the distribution
    y : numpy.ndarray
        the y-values of the distribution

    """
    xstart = mean - (4.0 * stdev)
    xend = mean + (4.0 * stdev)
    x = np.linspace(xstart,xend,num_pts)
    y = (1.0/np.sqrt(2.0*np.pi*stdev*stdev)) * np.exp(-1.0 * ((x - mean)**2)/(2.0*stdev*stdev))
    return x,y