\begin{equation} \label{eq-SM}
\begin{aligned}
&S_{M, \lambda}(f) = -\frac{1}{M}\sum_{i=1}^{n}\sum_{j=1}^{N_i}\{Y_{ij} - f(T_{ij})\}K_{T_{ij}} + W_\lambda f \triangleq S_{M}(f) + W_\lambda f, \\
&DS_{M, \lambda}(f)\Delta g = \frac{1}{M}\sum_{i=1}^{n}\sum_{j=1}^{N_i}\Delta g(T_{ij})K_{T_{ij}} + W_\lambda\Delta g.
\end{aligned}
\end{equation}
