def calc_cov(X, Y):
    return (np.sum(((X - np.average(X)) * (Y - np.average(Y)))) / (X.shape[0] - 1))
def calc_cov(X, Y):
    return (np.sum(((X - np.average(X)) * (Y - np.average(Y)))) / (X.shape[0] - 1))