[Tex/LaTex] put two algorithm side by side

algorithmslncspositioning

I want to put two algorithm side by side to gain place in the document, but when I use \documentclass{llncs} instead of \documentclass{article}, the following code does not work (errors):

\documentclass{article}
\usepackage[margin=1in]{geometry}% http://ctan.org/pkg/geometry
\usepackage{lipsum}% http://ctan.org/pkg/lipsum
\usepackage{algorithm}% http://ctan.org/pkg/algorithm
\usepackage{algpseudocode}% http://ctan.org/pkg/algorithmicx
\usepackage{caption}% http://ctan.org/pkg/caption
\begin{document}
\lipsum[1]

\medskip

\noindent\begin{minipage}{.5\textwidth}
\captionof{algorithm}{Euclid’s algorithm}\label{algo1}
\begin{algorithmic}[1]
  \Procedure{Euclid}{$a,b$}\Comment{The g.c.d. of a and b}
    \State $r\gets a\bmod b$
    \While{$r\not=0$}\Comment{We have the answer if r is 0}
      \State $a\gets b$
      \State $b\gets r$
      \State $r\gets a\bmod b$
    \EndWhile
    \State \textbf{return} $b$\Comment{The gcd is b}
  \EndProcedure
\end{algorithmic}
\end{minipage}%
\begin{minipage}{.5\textwidth}
\captionof{algorithm}{Euclid’s algorithm}\label{algo2}
\begin{algorithmic}[1]
  \Procedure{Euclid}{$a,b$}\Comment{The g.c.d. of a and b}
    \State $r\gets a\bmod b$
    \While{$r\not=0$}\Comment{We have the answer if r is 0}
      \State $a\gets b$
      \State $b\gets r$
      \State $r\gets a\bmod b$
    \EndWhile
    \State \textbf{return} $b$\Comment{The gcd is b}
  \EndProcedure
\end{algorithmic}
\end{minipage}

\medskip

On the left is Algorithm~\ref{algo1}. On the right is Algorithm~\ref{algo2}.

\lipsum[2]

\end{document}

Best Answer

The problem is that the class file defines the caption commands and caption package hates it.

As the package author of caption and subcaption, Alex Sommerfeldt mentions this problem in this answer Subcaption package: compatibility issue with a problem related to (again) another class file. 

\captionsetup{compatibility=false}

would make the problem go away but might introduce others if the class file is picky about caption settings.

I have made up another solution for the algorithms though not sure if that's what you want: The first difference is that I have used the subcaption package instead of minipages. And then I cooked up a simple subalgorithm environment. And also placed them in a float (a table but can also be a figure too regarding the counters involved if needed). 

\documentclass{llncs}
\usepackage[margin=1in]{geometry}% http://ctan.org/pkg/geometry
\usepackage{lipsum}% http://ctan.org/pkg/lipsum
\usepackage{algorithm}% http://ctan.org/pkg/algorithm
\usepackage{algpseudocode}% http://ctan.org/pkg/algorithmicx

\usepackage{subcaption}% http://ctan.org/pkg/subcaption
\captionsetup{compatibility=false}
\DeclareCaptionSubType*{algorithm}
\renewcommand\thesubalgorithm{\thetable\alph{subalgorithm}}
\DeclareCaptionLabelFormat{alglabel}{Alg.~#2}



\title{My title}
\author{TeX.SX}
\institute{Online}

\begin{document}
\maketitle
\lipsum[1]
\begin{table}%
\begin{subalgorithm}{.5\textwidth}
\begin{algorithmic}[1]
  \Procedure{Euclid}{$a,b$}\Comment{The g.c.d. of a and b}
    \State $r\gets a\bmod b$
    \While{$r\not=0$}\Comment{We have the answer if r is 0}
      \State $a\gets b$
      \State $b\gets r$
      \State $r\gets a\bmod b$
    \EndWhile
    \State \textbf{return} $b$\Comment{The gcd is b}
  \EndProcedure
\end{algorithmic}
\caption{Euclid’s algorithm}\label{algo1}
\end{subalgorithm}%
\begin{subalgorithm}{.5\textwidth}
\begin{algorithmic}[1]
  \Procedure{Euclid}{$a,b$}\Comment{The g.c.d. of a and b}
    \State $r\gets a\bmod b$
    \While{$r\not=0$}\Comment{We have the answer if r is 0}
      \State $a\gets b$
      \State $b\gets r$
      \State $r\gets a\bmod b$
    \EndWhile
    \State \textbf{return} $b$\Comment{The gcd is b}
  \EndProcedure
\end{algorithmic}
\caption{Euclid’s algorithm}\label{algo2}
\end{subalgorithm}
\captionsetup{labelformat=alglabel}
\caption{Two algorithms}%
\label{tab:1}%
\end{table}


On the left is Algorithm~\ref{algo1}. On the right is Algorithm~\ref{algo2}.

\lipsum[2]

\end{document}

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