How to get a "tight" boxed algorithm with the algorithm2e package

Question

I am using the algorithm2e package for my pseudo code since I like the like the options this package offers. However, the boxed option gives a text-width sized box and it doesn't look appealing to me when the code is much more narrow. This is a MWE.

\documentclass{book}
\usepackage[utf8]{inputenc}
\usepackage{amsmath} %
\usepackage{amssymb}

% real R
\newcommand{\R}{\mathbb{R}}

\usepackage[noline, boxed]{algorithm2e}

\begin{document}

 % ALGORITHM
 \begin{algorithm}
 \DontPrintSemicolon
 % \SetKwData{Left}{left} % normal
 \SetKwFunction{SDud}{SDud}\SetKwFunction{Tol}{tol}\SetKwFunction{Break}{break}% tt
 \SetKwInOut{Input}{input}
 \BlankLine
 \Input{$A \in \R^{m \times n} (m<n), \:\: b \in \R^m, \:\: x_{(0)}\in \R^n$.}
 \BlankLine
 \emph{\% Initialization}\;
 $x = x_{(0)}$\;
 $r = b - Ax$\;
 $p = A^Tr$\;
 \BlankLine
 \emph{\% Start \SDud}\;
 \For{$t = 0,1,2\ldots,t_{\max}$}{
  \BlankLine
  \emph{\% Compute $\alpha_{(t)}$}\;
  $q = Ap$ \;
  $\rho = p^Tp, \: \sigma = q^Tq, \: \alpha = \rho / \sigma$ \;
  \BlankLine
  \emph{\% Check for convergence}\;
  \lIf{$\rho \leq$ \Tol}{\Break}
  \BlankLine
  \emph{\% Compute new iterate $x_{(t+1)}$}\;
  $x \leftarrow x + \alpha p$
  \BlankLine
  \emph{\% Update residual $p_{(t+1)}$}\;
  $w = A^Tq$ \;
  $p \leftarrow p - \alpha w$
 }
 \caption{My alg}
 \end{algorithm}

\end{document}

And this is how it looks:

I don't like the white space on the right, so I wish it was a tight, centered box around the pseudo code. Unfortunately the algorithm2e documentation doesn't provide me with any insight regarding this issue. Can somebody here help me out?

Cheerse

Answer 1

This is adapted from Thomas F. Sturm's solution to this question. You can make your algorithm unfloatable and box it within another floatable environment---in this case, an invisible tcolorbox. Change the width variable to adapt the box around your algorithm.

\documentclass{book}
\usepackage[utf8]{inputenc}
\usepackage{amsmath} %
\usepackage{amssymb}
\usepackage[noline,boxed]{algorithm2e}
\usepackage[skins]{tcolorbox}

% real R
\newcommand{\R}{\mathbb{R}}

\begin{document}

\begin{tcolorbox}[blanker,width=(\linewidth-3.5cm)]
\begin{algorithm}[H]
 \DontPrintSemicolon
 % \SetKwData{Left}{left} % normal
 \SetKwFunction{SDud}{SDud}\SetKwFunction{Tol}{tol}\SetKwFunction{Break}{break}% tt
 \SetKwInOut{Input}{input}
 \BlankLine
 \Input{$A \in \R^{m \times n} (m<n), \:\: b \in \R^m, \:\: x_{(0)}\in \R^n$.}
 \BlankLine
 \emph{\% Initialization}\;
 $x = x_{(0)}$\;
 $r = b - Ax$\;
 $p = A^Tr$\;
 \BlankLine
 \emph{\% Start \SDud}\;
 \For{$t = 0,1,2\ldots,t_{\max}$}{
  \BlankLine
  \emph{\% Compute $\alpha_{(t)}$}\;
  $q = Ap$ \;
  $\rho = p^Tp, \: \sigma = q^Tq, \: \alpha = \rho / \sigma$ \;
  \BlankLine
  \emph{\% Check for convergence}\;
  \lIf{$\rho \leq$ \Tol}{\Break}
  \BlankLine
  \emph{\% Compute new iterate $x_{(t+1)}$}\;
  $x \leftarrow x + \alpha p$
  \BlankLine
  \emph{\% Update residual $p_{(t+1)}$}\;
  $w = A^Tq$ \;
  $p \leftarrow p - \alpha w$
 }
 \caption{My alg}
\end{algorithm}
\end{tcolorbox}

\end{document}

My result looks like this:

Answer 2

I have found a solution from other topics, though not the most elegant one I suppose. You can do it with minpages but then you have to give your algorthm environment the [H] specifier such that it isn't a float anymore. I'd prefer if it would remain a float but it will do...

Here's an example

\begin{center}
\begin{minipage}{0.7\textwidth}
\begin{algorithm}[H]
 \DontPrintSemicolon
 % \SetKwData{Left}{left} % normal
 \SetKwFunction{SDud}{SDud}\SetKwFunction{Tol}{tol}\SetKwFunction{Break}{break}% tt
 \SetKwInOut{Input}{input}
 \BlankLine
 \Input{$A \in \R^{m \times n} (m<n), \:\: b \in \R^m, \:\: x_{(0)}\in \R^n$.}
 \BlankLine
 \emph{\% Initialization}\;
 $x = x_{(0)}$\;
 $r = b - Ax$\;
 $p = A^Tr$\;
 \BlankLine
 \emph{\% Start \SDud}\;
 \For{$t = 0,1,2\ldots,t_{\max}$}{
  \BlankLine
  \emph{\% Compute $\alpha_{(t)}$}\;
  $q = Ap$ \;
  $\rho = p^Tp, \: \sigma = q^Tq, \: \alpha = \rho / \sigma$ \;
  \BlankLine
  \emph{\% Check for convergence}\;
  \lIf{$\rho \leq$ \Tol}{\Break}
  \BlankLine
  \emph{\% Compute new iterate $x_{(t+1)}$}\;
  $x \leftarrow x + \alpha p$
  \BlankLine
  \emph{\% Update residual $p_{(t+1)}$}\;
  $w = A^Tq$ \;
  $p \leftarrow p - \alpha w$
 }
 \caption{My alg}
 \end{algorithm}
\end{minipage}
\end{center}

Any improvements are welcome still.

Answer 3

I would suggest to use the figure environment as a wrapper to keep the algorithm as a float. Without adding a caption or label in the figure you should not have problems with the \listoffigures

\begin{figure}[htb]
    \centering
    \begin{minipage}{.7\linewidth}
    \begin{algorithm}[H]
        \KwData{this text}
        \KwResult{how to write algorithm with \LaTeX2e }
        initialization\;
        \While{not at end of this document}{
            read current\;
            \eIf{understand}{
                go to next section\;
                current section becomes this one\;
            }{
                go back to the beginning of current section\;
            }
        }
        \caption{How to write algorithms}
        \label{algo:black draw}
    \end{algorithm}
  \end{minipage}
\end{figure}

You could also go to a cleaner solution as defining a new env to wrap everything as described in this topic