1、Latex中将字母上下方插入字母数字\mathop{a}\limits_{i=1}：
a
i
=
1
\mathop{a}\limits_{i=1}
i=1a
2Latex罗马数字
大写：\uppercase\expandafter{\romannumeral20}
小写：\romannumeral20
2、LaTex一行排列多个图，并且加入每个图都添加小标题
效果：
代码：
\begin{figure}[!ht]
\centering
\begin{subfigure}[b]{0.99\textwidth}
\fontsize{10.0pt}{\baselineskip}\selectfont
\rotatebox{90}{~~~~~~~~[29]}
\begin{minipage}[t]{0.185\linewidth}
\centering
\includegraphics[width=1\linewidth]{pic3/voc101.pdf}
\end{minipage}
\begin{minipage}[t]{0.185\linewidth}
\centering
\includegraphics[width=1\linewidth]{pic3/voc102.pdf}
\end{minipage}
\begin{minipage}[t]{0.185\linewidth}
\centering
\includegraphics[width=1\linewidth]{pic3/voc103.pdf}
\end{minipage}
\begin{minipage}[t]{0.185\linewidth}
\centering
\includegraphics[width=1\linewidth]{pic3/voc104.pdf}
\end{minipage}
\begin{minipage}[t]{0.185\linewidth}
\centering
\includegraphics[width=1\linewidth]{pic3/voc105.pdf}
\end{minipage}
%\caption{}
\label{fig:3-11-1V}
\end{subfigure}%
\\
\begin{subfigure}[b]{0.99\textwidth}
\fontsize{10.0pt}{\baselineskip}\selectfont
\rotatebox{90}{~~~~~~~~[29]}
\begin{minipage}[t]{0.185\linewidth}
\centering
\includegraphics[width=1\linewidth]{pic3/voc101.pdf}
\end{minipage}
\begin{minipage}[t]{0.185\linewidth}
\centering
\includegraphics[width=1\linewidth]{pic3/voc102.pdf}
\end{minipage}
\begin{minipage}[t]{0.185\linewidth}
\centering
\includegraphics[width=1\linewidth]{pic3/voc103.pdf}
\end{minipage}
\begin{minipage}[t]{0.185\linewidth}
\centering
\includegraphics[width=1\linewidth]{pic3/voc104.pdf}
\end{minipage}
\begin{minipage}[t]{0.185\linewidth}
\centering
\includegraphics[width=1\linewidth]{pic3/voc105.pdf}
\end{minipage}
%\caption{}
\label{fig:3-11-2Lap}
\end{subfigure}
\\
\begin{subfigure}[b]{0.99\textwidth}
\fontsize{10.0pt}{\baselineskip}\selectfont
\rotatebox{90}{~~~~~~~~[29]}
\begin{minipage}[t]{0.185\linewidth}
\centering
\includegraphics[width=1\linewidth]{pic3/voc101.pdf}
\end{minipage}
\begin{minipage}[t]{0.185\linewidth}
\centering
\includegraphics[width=1\linewidth]{pic3/voc102.pdf}
\end{minipage}
\begin{minipage}[t]{0.185\linewidth}
\centering
\includegraphics[width=1\linewidth]{pic3/voc103.pdf}
\end{minipage}
\begin{minipage}[t]{0.185\linewidth}
\centering
\includegraphics[width=1\linewidth]{pic3/voc104.pdf}
\end{minipage}
\begin{minipage}[t]{0.185\linewidth}
\centering
\includegraphics[width=1\linewidth]{pic3/voc105.pdf}
\end{minipage}
%\caption{}
\label{fig:3-11-3Fillet}
\end{subfigure}%
\bicaption{不同类型的焊接工件。(a) 对接接头，(b) 搭接接头，(c) 角接接头。}{Different types of welding workpieces. (a) Butt joint, (b) Lap joint, (c) Fillet joint.}
\label{fig:weldingworkpiece}
\end{figure}
3、效果
代码：
\begin{figure}[!ht]
\centering
\begin{subfigure}[b]{0.23\textwidth}%控制sufigure宽度
\begin{minipage}[t]{0.9\linewidth}
\includegraphics[width=1\linewidth]{pic3/voc101.pdf}\vspace{4pt}
\includegraphics[width=1\linewidth]{pic3/voc102.pdf}\vspace{4pt}
\includegraphics[width=1\linewidth]{pic3/voc103.pdf}\vspace{4pt}
\includegraphics[width=1\linewidth]{pic3/voc104.pdf}\vspace{4pt}
\includegraphics[width=1\linewidth]{pic3/voc105.pdf}
\end{minipage}
\caption{}
\label{fig:3-11-1V}
\end{subfigure}%
\begin{subfigure}[b]{0.23\textwidth}
\begin{minipage}[t]{0.9\linewidth}
\includegraphics[width=1\linewidth]{pic3/voc101.pdf}\vspace{4pt}
\includegraphics[width=1\linewidth]{pic3/voc102.pdf}\vspace{4pt}
\includegraphics[width=1\linewidth]{pic3/voc103.pdf}\vspace{4pt}
\includegraphics[width=1\linewidth]{pic3/voc104.pdf}\vspace{4pt}
\includegraphics[width=1\linewidth]{pic3/voc105.pdf}
\end{minipage}
\caption{}
\label{fig:3-11-2Lap}
\end{subfigure}
\begin{subfigure}[b]{0.23\textwidth}
\begin{minipage}[t]{0.9\linewidth}
\includegraphics[width=1\linewidth]{pic3/voc101.pdf}\vspace{4pt}
\includegraphics[width=1\linewidth]{pic3/voc102.pdf}\vspace{4pt}
\includegraphics[width=1\linewidth]{pic3/voc103.pdf}\vspace{4pt}
\includegraphics[width=1\linewidth]{pic3/voc104.pdf}\vspace{4pt}
\includegraphics[width=1\linewidth]{pic3/voc105.pdf}
\end{minipage}
\caption{}
\label{fig:3-11-3Fillet}
\end{subfigure}%
\bicaption{不同类型的焊接工件。(a) 对接接头，(b) 搭接接头，(c) 角接接头。}{Different types of welding workpieces. (a) Butt joint, (b) Lap joint, (c) Fillet joint.}
\label{fig:weldingworkpiece}
\end{figure}
参考文献：
https://blog.csdn.net/qq_37424778/article/details/120882254
