Text Formatting ⇒ Putting two Algorithms Side by Side

[pablochacin]

Hi

I'm trying to put two algorithm listings side by side within an figure environment, to refer them as sub-figures. I tried many, many options, but none has worked so far.

The "obvious" approach, putting subfloats in the figure, as shown below, throws the infamous error "! LaTeX Error: Something's wrong--perhaps a missing \item."

Code: Select all

\begin{figure}[h]
\centering

\subfloat[Algorithms 1]{
\begin{algorithmic}
% algorithm text
\end{algorithmic}
}

\subfloat[algorithm 2]{
\begin{algorithmic}
% algorithm text
\end{algorithmic}
}

\caption{Algorithms}
\label{figure
\end{figure}

Is there any simple way to do this? Looks like a common problem, bu googling has been mostly useless.

Thanks in advance

[gmedina]

Hi,

one possibility would be to use minipages and the \captionof command provided by the caption package (see Remarks below); the following example illustrates this approach:

Code: Select all

\documentclass{article}
\usepackage{algorithm}
\usepackage{algorithmic}
\usepackage{caption}

\begin{document}

\noindent\begin{minipage}{\textwidth}
  \centering
  \begin{minipage}{.45\textwidth}
    \centering
    \captionof{algorithm}{test algorithm 1}
    \label{alg:alg1}
    \begin{algorithmic}
    \WHILE{$N \neq 0$}
    \IF{$N$ is even}
    \STATE $X \Leftarrow X \times X$
    \STATE $N \Leftarrow N / 2$
    \ENDIF
    \ENDWHILE
    \end{algorithmic}
  \end{minipage}
  \begin{minipage}{.45\textwidth}
    \centering
    \captionof{algorithm}{test algorithm 2}
    \label{alg:alg2}
    \begin{algorithmic}
    \WHILE{$N \neq 0$}
    \IF{$N$ is even}
    \STATE $X \Leftarrow X \times X$
    \STATE $N \Leftarrow N / 2$
    \ENDIF
    \ENDWHILE
    \end{algorithmic}
  \end{minipage}
  \captionof{figure}{Two algorithms side by side}
  \label{fig:twoalg}
\end{minipage}

Figure~\ref{fig:twoalg} shows two algorithms side by side: they can be referenced as algorithm~\ref{alg:alg1} and algorithm~\ref{alg:alg2}...

\end{document}

Remarks: 1) Make sure that you have a recent version (3.1x) of the package installed in your system.
2) Please take into account that since minipages were used this is not a floating object.

[steenreem]

For anyone searching this. I noticed that wrapping the algorithmic environment in a minipage removes the infamous error.

[localghost]

Can be done much easier with »subcaption« (bundled with caption).

Code: Select all

\documentclass[11pt,a4paper]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[font=small,labelfont=bf,tableposition=top]{caption}
\usepackage[font=footnotesize]{subcaption}
\usepackage{algorithmic}

\begin{document}
  \begin{figure}[!ht]
    \centering
    \begin{subfigure}{.45\textwidth}
      \centering
      \begin{algorithmic}
        \WHILE{$N \neq 0$}
          \IF{$N$ is even}
            \STATE $X \Leftarrow X \times X$
            \STATE $N \Leftarrow N / 2$
          \ENDIF
        \ENDWHILE
      \end{algorithmic}
      \caption{Test Algorithm No.1}\label{alg:alg-1}
    \end{subfigure}
		\hfill
    \begin{subfigure}{.45\textwidth}
      \centering
      \begin{algorithmic}
        \WHILE{$N \neq 0$}
          \IF{$N$ is even}
            \STATE $X \Leftarrow X \times X$
            \STATE $N \Leftarrow N / 2$
          \ENDIF
        \ENDWHILE
      \end{algorithmic}
      \caption{Test Algorithm No.2}\label{alg:alg-2}
    \end{subfigure}
    \caption{Two algorithms side by side}\label{fig:twoalg}
  \end{figure}

  Figure~\ref{fig:twoalg} shows two algorithms side by side: they can be referenced as algorithm~\ref{alg:alg-1} and algorithm~\ref{alg:alg-2}.
\end{document}

The package manual has more detailed explanations.


Thorsten