def plot_dist_normal(s, mu, sigma):
    """
    plot distribution
    """
    import matplotlib.pyplot as plt
    count, bins, ignored = plt.hist(s, 30, normed=True)
    plt.plot(bins, 1/(sigma * np.sqrt(2 * np.pi)) \
            * np.exp( - (bins - mu)**2 / (2 * sigma**2) ), \
            linewidth = 2, color = 'r')
    plt.show()