latex 竖排子图

latex中竖排子图，以\\标识子图换行。

\usepackage{graphicx}
\usepackage{float}
\usepackage{subfig}

\begin{figure}[tbp]
	\centering
	\subfloat[sub captain 1]{\label{fig:a}\includegraphics[width=1in]{placeholder}}\\
	\subfloat[sub captain 2]{\label{fig:b}\includegraphics[width=1in]{placeholder}}\\	
	\caption{Capital Roman numerals.}
\end{figure}