def METHOD_NAME(self, x, y, sigma0, Rs, e1, e2, center_x=0, center_y=0):
    """Returns df/dx and df/dy of the function (integral of NFW)"""
    x_, y_ = param_util.transform_e1e2_square_average(
        x, y, e1, e2, center_x, center_y
    )
    phi_G, q = param_util.ellipticity2phi_q(e1, e2)
    cos_phi = np.cos(phi_G)
    sin_phi = np.sin(phi_G)
    e = param_util.q2e(q)
    f_x_prim, f_y_prim = self.spherical.METHOD_NAME(x_, y_, sigma0, Rs)
    f_x_prim *= np.sqrt(1 - e)
    f_y_prim *= np.sqrt(1 + e)
    f_x = cos_phi * f_x_prim - sin_phi * f_y_prim
    f_y = sin_phi * f_x_prim + cos_phi * f_y_prim
    return f_x, f_y