def METHOD_NAME(self, x, y, n_sersic, r_eff, k_eff, center_x=0, center_y=0):
    """
    :param x:
    :param y:
    :param n_sersic:
    :param r_eff:
    :param k_eff:
    :param center_x:
    :param center_y:
    :return:
    """
    _dr = 0.00001
    x_ = x - center_x
    y_ = y - center_y
    r = np.sqrt(x_**2 + y_**2)
    alpha = self.alpha_abs(r, 0, n_sersic, r_eff, k_eff)
    alpha_dr = self.alpha_abs(r + _dr, 0, n_sersic, r_eff, k_eff)
    METHOD_NAME = (alpha_dr - alpha) / _dr
    return METHOD_NAME