figure in two column while using a one column environment

Question

I am using one column book class and I would like to have just one page in my document consisting of two figures spreading along two columns, as the example in below. I would appreciate if some one give me a straightforward way to do it (if possible)? PS: I have already tried multicols environment and \twocolumn command , but were not successful, I image it is because I wanted to use them in a float environment!

part of my code:

\begin{figure}
\centering
\begin{subfigure}{.5\textwidth}
  \centering
  \includegraphics[width=0.9\linewidth]{./chapter6/Figures/pw1.pdf}
  \caption{}
  \label{pw1}
 \end{subfigure}
\begin{subfigure}{.5\textwidth}
  \centering
  \includegraphics[width=0.9\linewidth]{./chapter6/Figures/pw2.pdf}
  \caption{}
  \label{pw2}
 \end{subfigure}
\begin{subfigure}{.5\textwidth}
  \centering
  \includegraphics[width=0.9\linewidth]{./chapter6/Figures/pw3.pdf}
  \caption{}
  \label{pw3}
 \end{subfigure}
 \caption{(a) .., (b) ..., and (c)....}
 \label{pw}
 \end{figure}
\begin{figure}
\centering
\begin{subfigure}{.5\textwidth}
  \centering
  \includegraphics[width=0.9\linewidth]{./chapter6/Figures/pw11.pdf}
  \caption{}
  \label{pw11}
 \end{subfigure}
\begin{subfigure}{.5\textwidth}
  \centering
  \includegraphics[width=0.9\linewidth]{./chapter6/Figures/pw12.pdf}
  \caption{}
  \label{pw12}
 \end{subfigure}
\begin{subfigure}{.5\textwidth}
  \centering
  \includegraphics[width=0.9\linewidth]{./chapter6/Figures/pw13.pdf}
  \caption{}
  \label{pw13}
 \end{subfigure}
 \caption{(a) .., (b) ..., and (c) ....}
 \label{pw1}
 \end{figure}

Answer 1

I assume you're using the subcaption package to set up the subfigure environments. If this assumption is correct, you may achieve your embedding your objective by (a) embedding two minipage environments inside a figure environment and (b) embedding three subcaption environments plus a \caption statement inside each of the two minipages. Note that it's possible to have two logical "figures" inside a figure float.

In the following code, the width of the minipage environments is set to 0.45\textwidth, while the widths of the subfigure environments and the included graphics is simply set to \linewidth. With this setup, no \centering instructions are required (or, indeed, be useful). The "1" at the top-right of the following screenshot is the page number.

\documentclass{book}
\usepackage[demo]{graphicx} % omit "demo" option in real document
\usepackage{subcaption}
\begin{document}
\begin{figure}[h!]  % "[h!]" used just for this example
\begin{minipage}{0.45\textwidth}

\begin{subfigure}{\linewidth} 
  \includegraphics[width=\linewidth]{pw1a.pdf}
  \caption{} \label{pw1a}
 \end{subfigure}

 \bigskip
 \begin{subfigure}{\linewidth}
  \includegraphics[width=\linewidth]{pw1b.pdf}
  \caption{} \label{pw1b}
 \end{subfigure}

 \bigskip
 \begin{subfigure}{\linewidth}  
  \includegraphics[width=\linewidth]{pw1c.pdf}
  \caption{} \label{pw1c}
 \end{subfigure}

\caption{Three subfigures} \label{fig:3subfigs}
\end{minipage}
\hspace{\fill}  %% crucial: no blank lines around this command
\begin{minipage}{0.45\textwidth}

 \begin{subfigure}{\linewidth}  
  \includegraphics[width=\linewidth]{pw2a.pdf}
  \caption{} \label{pw2a}
 \end{subfigure}

 \bigskip
 \begin{subfigure}{\linewidth}  
  \includegraphics[width=\linewidth]{pw2b.pdf}
  \caption{} \label{pw2b}
 \end{subfigure}

 \bigskip
 \begin{subfigure}{\linewidth}  
  \includegraphics[width=\linewidth]{pw2c.pdf}
  \caption{} \label{pw2c}
 \end{subfigure}

\caption{Three more subfigures} \label{fig:3moresubfigs}
\end{minipage}
\end{figure}
\end{document}