图片并排显示

\begin{figure}[H]
    \centering
    \subfigure[Before optimization]{
        \begin{minipage}{4cm}
            \centering
            \includegraphics[width=4cm]{pic1.png}    
        \end{minipage}%
    }%
    \subfigure[After optimization]{
        \begin{minipage}{4cm}
            \centering
            \includegraphics[width=4cm]{pic2.png}    
        \end{minipage}%
    }%
    \subfigure[Real structure]{
        \begin{minipage}{4cm}
            \centering
            \includegraphics[width=4cm]{pic3.png}    
        \end{minipage}%
    }%
    \caption{Earthquake data set}
\end{figure}