```tex \begin{figure} \begin{minipage}[t]{0.35\linewidth} \centering \includegraphics[height=4.5cm,width=7.5cm]{Fig1.eps} \caption{The system output $y(k)$ and the reference signal $y_{d}(k)$.} \end{minipage}% \hfill \begin{minipage}[t]{0.5\linewidth} \centering \includegraphics[height=4.5cm,width=7.5cm]{Fig2.eps} \caption{The output tracking error $y(k)-y_d(k)$.} \end{minipage} \end{figure} \begin{figure} \begin{minipage}[t]{0.35\linewidth} \centering \includegraphics[height=4.5cm,width=7.5cm]{Fig3.eps} \caption{The input signal $w(k)$.} \end{minipage}% \hfill \begin{minipage}[t]{0.5\linewidth} \centering \includegraphics[height=4.5cm,width=7.5cm]{Fig4.eps} \caption{The norm of the weight vectors $\|\hat{\varpi}\left( k\right)\| $ and $\|\hat{\varpi}_{c}\left( k\right)\| $.} \end{minipage} \end{figure} \begin{figure} \begin{minipage}[t]{0.35\linewidth} \centering \includegraphics[height=4.5cm,width=7.5cm]{Fig5.eps} \caption{Threshold and event-triggered error.} \end{minipage}% \hfill \begin{minipage}[t]{0.5\linewidth} \centering \includegraphics[height=4.5cm,width=7.5cm]{Fig6.eps} \caption{The accumulative number of the event-triggered events.} \end{minipage} \end{figure} ```