在科研論文寫作中，有時候為了橫向、縱向對比或者節省空間，我們需要畫子圖，在MATLAB中可以通過subplot命令來實現。在Latex中有以下幾種方法進行子圖的繪製：
- 使用subfig巨集包（有可能與hyperref巨集包衝突，推薦使用subcaption巨集包），主要格式為：

  \begin{figure}
  \subfloat[]{}
  \subfloat[]{}\\
  \subfloat[]{}
  \subfloat[]{}
  \end{figure}

• 使用subcaption巨集包，主要格式為：

  \begin{figure}
  \subcaptionbox{}
 
{}
  \subcaptionbox{}{}\\
  \subcaptionbox{}{}
  \subcaptionbox{}{}
  \end{figure}

• 使用groupplot巨集包，主要格式為：

  \begin{figure}
\centering
\begin{tikzpicture}
\begin{groupplot}
\nextgroupplot
\addplot {x};
\nextgroupplot
\end{groupplot}
\end{tikzpicture}
\end{figure}

• 使用matrix巨集包，主要格式為：

    \begin{figure}
 

\centering
\begin{tikzpicture}
\matrix
 {
 \begin{axis}
 \addplot {x};
 \end{axis}

  \begin{axis}
 \addplot {x};
 \end{axis}
 }
\end{tikzpicture}
\end{figure}

下面給出上述各種情況的具體程式碼實現以及示意圖：
- 使用subfig巨集包

程式碼如下：

\documentclass{article}
\usepackage[dvipdfm]{graphicx}
\def\pgfsysdriver{pgfsys-dvipdfmx.def}
 

\usepackage{tikz}
\usepackage{pgfplots}
\usepackage{subfig}%使用子圖包，可能與hyperref衝突
\usepackage{float}
\usepackage{cite}
\usepackage[colorlinks,dvipdfm,
            pdfpagemode=UseOutlines,
            pdfstartview=FitH,
            anchorcolor=green,
            citecolor=blue,
            linkcolor=red,
            hyperindex=true,
            pagebackref,
            bookmarksnumbered,
            bookmarksopenlevel=2,
            colorlinks]{hyperref}

\pgfplotsset{width=6cm,compat=1.15}

\begin{document}
\begin{figure}
\begin{center}
\subfloat[\label{subfig1}]{
\begin{tikzpicture}
\begin{axis}[
legend columns=-1,%the legend are plotted horizontally
legend entries={$x$},
legend to name=named,% stored in named, not plotted in the figure
title={subfig1},
]
\addplot {x};\label{curvex}
\end{axis}
\end{tikzpicture}\label{subfig2}}
\subfloat[]{
\begin{tikzpicture}
\begin{axis}[title={subfig2}]
\addplot {x};
\end{axis}
\end{tikzpicture}\label{subfig2}}
\end{center}
\caption{\hspace{1em}Two subfigures.}\label{f1}
\end{figure}
As depicted in Figures~\ref{subfig1} and \ref{subfig2}, the subfigures of Figure~\ref{f1}, \ref{curvex} represents function $f(x)=x$.

\end{document} 

• 使用subcaption巨集包
  
  程式碼如下：

\documentclass{article}
\usepackage[dvipdfm]{graphicx}
\def\pgfsysdriver{pgfsys-dvipdfmx.def}
\usepackage{tikz}
\usepackage{pgfplots}
%\usepackage{subfig}
\usepackage[hypcap=true,labelsep=period,font=small]{caption}% 圖的標題設定Fig.
\usepackage[hypcap=true]{subcaption}%用於畫子圖 可以適配hyperref包
\usepackage{float}
\usepackage[colorlinks,dvipdfm,
            pdfpagemode=UseOutlines,
            pdfstartview=FitH,
            anchorcolor=green,
            citecolor=blue,
            linkcolor=red,
            hyperindex=true,
            pagebackref,
            bookmarksnumbered,
            bookmarksopenlevel=2,
            colorlinks]{hyperref}
\pgfplotsset{width=6cm,compat=1.15}
\begin{document}
\begin{figure}
\begin{center}
\subcaptionbox{\label{subfig1}}{
\begin{tikzpicture}
\begin{axis}[
legend columns=-1,%the legend are plotted horizontally
legend entries={$x$},
legend to name=named,% stored in named
title={subfig1},
]
\addplot {x};\label{curvex}
\end{axis}
\end{tikzpicture}}
\subcaptionbox{\label{subfig2}}{
\begin{tikzpicture}
\begin{axis}[title={subfig2}]
\addplot {x};
\end{axis}
\end{tikzpicture}}
\end{center}
\caption{\hspace{1em}Two subfigures.}\label{f1}
\end{figure}

As depicted in Figures~\ref{subfig1} and \ref{subfig2}, the subfigures of Figure~\ref{f1}, \ref{curvex} represents function $f(x)=x$.

\end{document} 

• 使用groupplot巨集包
  
  程式碼如下：

\documentclass{article}
\usepackage[dvipdfm]{graphicx}
\def\pgfsysdriver{pgfsys-dvipdfmx.def}
\usepackage{tikz}
\usepackage{pgfplots}
\pgfplotsset{width=7cm,compat=1.15}
\usepgfplotslibrary{groupplots}
\usepackage{caption}
\usepackage{subcaption}
\usepackage[colorlinks,dvipdfm,
            pdfpagemode=UseOutlines,
            pdfstartview=FitH,
            anchorcolor=green,
            citecolor=blue,
            linkcolor=red,
            hyperindex=true,
            pagebackref,
            bookmarksnumbered,
            bookmarksopenlevel=2,
            colorlinks]{hyperref}
\begin{document}
\begin{figure}[htb]
\centering
\begin{tikzpicture}
\begin{groupplot}[
group style={
group name=my plots,
group size=2 by 2,
xlabels at=edge bottom,
xlabels at=all,
ylabels at=edge left,
x descriptions at=edge bottom,
},
footnotesize,
width=6cm,
height=6cm,
%
xlabel=$x$,
ylabel=$f(x)$,
]
\nextgroupplot
\addplot {x};
\node [text width=1em,anchor=north west] at (rel axis cs: 0,1)
                {\subcaption{\label{f11}}};%<- changed
\nextgroupplot
\addplot {x^2};
\nextgroupplot
\addplot {x^3};
\nextgroupplot
\addplot {x^4};
\end{groupplot}
\end{tikzpicture}
\caption{\hspace{1em}Four subfigures.}\label{f1}
\end{figure}
How to refer to subfigure~\ref{f11} in Figure~\ref{f1}.

\end{document} 

• 使用matrix巨集包
  
  程式碼如下：

\documentclass{article}
\usepackage[dvipdfm]{graphicx}
\def\pgfsysdriver{pgfsys-dvipdfmx.def}
\usepackage{tikz}
\usepackage{pgfplots}
\pgfplotsset{width=7cm,compat=1.15}
\usepgfplotslibrary{groupplots}
\usetikzlibrary{matrix}
\usepackage{caption}
\usepackage{subcaption}
\usepackage[colorlinks,dvipdfm,
            pdfpagemode=UseOutlines,
            pdfstartview=FitH,
            anchorcolor=green,
            citecolor=blue,
            linkcolor=red,
            hyperindex=true,
            pagebackref,
            bookmarksnumbered,
            bookmarksopenlevel=2,
            colorlinks]{hyperref}
\begin{document}
\begin{figure}[htb]
\centering
\begin{tikzpicture}
\pgfplotsset{small}
\matrix {
\begin{axis}[ylabel={$f(x)=x$},ylabel style={font=\small}]
\addplot {x};
\node [text width=1em,anchor=north west] at (rel axis cs: 0,1)
                {\subcaption{\label{f11}}};%<- changed
\end{axis}
&
% differently large labels are aligned automatically:
\begin{axis}[ylabel={$f(x)=x^2$},ylabel style={font=\small}]
\addplot {x^2};
\end{axis}
\\
\begin{axis}[ylabel={$f(x)=x^3$},ylabel style={font=\small},xlabel=$x$,xlabel style={font=\small}]
\addplot {x^3};
\end{axis}
&
\begin{axis}[ylabel={$f(x)=x^4$},ylabel style={font=\small},xlabel=$x$,xlabel style={font=\small}]
\addplot {x^4};
\end{axis}
\\
};
\end{tikzpicture}
\caption{\hspace{1em}Four subfigures.}\label{f1}
\end{figure}
How to refer to subfigure~\ref{f11} in Figure~\ref{f1}.

\end{document} 

Note: 第三種和第四種方法不適合需要單獨引用每一個子圖的情況，比較適合把四張圖看成一個整體的情況。