Change line number only after \; in algorithm2e

Question

How can I have the regular behaviour of some paragraphs placed together, without changing line number in the algorithm after one paragraph ends?

I want that line number changes only after a \; appears and having the paragraphs indented as usual.

The contents of \If, \For, \While, must follow the same rule: only numerate a line after \;.

So, next MWE would have six numbered lines (assuming that lines of the start and end of block are numbered): two lines for the start and end of \While block, two lines for its contents and two lines for the next paragraphs.

\documentclass[oneside]{memoir}
\usepackage[linesnumbered]{algorithm2e}
\DontPrintSemicolon
\begin{document}
\begin{algorithm}[H]
\While{$i < n$}{
First line numbered...
First line continues in new paragraph...
first line ends.;
Second line.;
}
First line numbered...
First line continues in new paragraph...
first line ends.;
Second line starts...
Second line continues in new paragraph...
second line ends.;
\end{algorithm}
\end{document}

Werner · Answer 1 · 2021-11-24T23:36:45.520

1

You can set the content inside its own block (like a fixed-width \parbox that is anchored at the [t]op):

\documentclass{article}
\usepackage[linesnumbered]{algorithm2e}
\DontPrintSemicolon
\begin{document}
\begin{algorithm}[H]
  First line numbered\ldots
First line continues in new paragraph\ldots
  first line ends.;
Second line starts\ldots
Second line continues in new paragraph\ldots
  second line ends.;
\end{algorithm}
\begin{algorithm}[H]
  \parbox[t]{\dimexpr\algowidth-2\algomargin}{First line numbered\ldots
First line continues in new paragraph\ldots
  first line ends.};
  \vspace{-\baselineskip}
  \parbox[t]{\dimexpr\algowidth-2\algomargin}{Second line starts\ldots
Second line continues in new paragraph\ldots
  second line ends.};
  \vspace{-\baselineskip}
\end{algorithm}
\end{document}

Another, automated way of handling this is to change \nl so that it only prints a numbered line once and then deactivates itself. Additionally, let \; temporarily reactivate \nl before shutting it down again. The redefinition of these macros are done using a hook into the \begin part of the algorithm environment.

\documentclass{article}
\usepackage[linesnumbered]{algorithm2e}
\DontPrintSemicolon
\makeatletter
\AddToHook{env/algorithm/begin}{%
  % At the start of algorithm, make \nl only print something once
  \let\oldnl\nl
  \def\nl{\oldnl\let\nl\relax}
  \let\old@endalgoln@endalgoln
  % Update ; (or @endalgoln) to do the same thing
  \renewcommand{@endalgoln}{%
    \def\nl{\oldnl\let\nl\relax}%
    \old@endalgoln
  }
}
\makeatother
\begin{document}
\begin{algorithm}[H]
  First line numbered\ldots
First line continues in new paragraph\ldots
  first line ends.;
Second line starts\ldots
Second line continues in new paragraph\ldots
  second line ends.;
\end{algorithm}
\end{document}

_{I'm not sure whether this may break other components of the algorithm structure.}

edited Nov 24 '21 at 23:36

answered Nov 24 '21 at 22:40

Werner

603,163

Thanks, I'd prefer something that leaves unchanged the MWE (like redefine \; and \nl commands or something else). – Alberto López Nov 24 '21 at 23:04
@AlbertoLópez: You're going to have to intervene in the code somehow if you're expecting the code to deliver something other than the default. Just saying... – Werner Nov 24 '21 at 23:05
@AlbertoLópez: You can also consider this as an option (maybe less invasive): Algorithm2e - Disabling line numbers for specific lines – Werner Nov 24 '21 at 23:06
Yes, that is my last option, but I'm almost sure that it can be done redefining \; and \nl (which I already did but without success) or something similar. It would be more elegant solution, avoiding putting a command at the beginning of every par. – Alberto López Nov 24 '21 at 23:11
@AlbertoLópez: Automation suggests you have to do this hundreds of times, making manual intervention error-prone. Am I correct? – Werner Nov 24 '21 at 23:17
That is correct, saving time and energy. – Alberto López Nov 24 '21 at 23:28
@AlbertoLópez: See the updated answer that redefines \nl and \; (actually \@endalgoln) to achieve your goal. I'm not confident this will break other things within an algorithm. – Werner Nov 24 '21 at 23:37
Thanks, I'll test it, it only remains indenting like in normal text, but it's a great progress. – Alberto López Nov 24 '21 at 23:42
The \AddToHook command isn't been recognized, which package does it belongs?, it seems it's a kernel problem, can't be solved with other well known commands? – Alberto López Nov 25 '21 at 00:06
@AlbertoLópez: You need to update your distribution, as this has been incorporated into the LaTeX kernel since Oct 2020. As an alternative, add \usepackage{xparse} before \AddToHook. – Werner Nov 25 '21 at 00:09
I already added \usepackage{xparse} and error still appears. – Alberto López Nov 25 '21 at 00:13
I only use the redefinition of commands (content of \AddToHook) and it works for text paragraphs but lines inside macros like \While, \For, etc are not being correctly numbered. – Alberto López Nov 25 '21 at 00:20
@AlbertoLópez: Here's a suggestion: Provide a complete, minimal example that replicates your current setup and also provides edge cases that need to be addressed. Read this for more details on how to present an MWE: I've just been asked to write a minimal working example (MWE), what is that? – Werner Nov 25 '21 at 00:23
Done, I edited it with more detail. – Alberto López Nov 25 '21 at 16:31

Change line number only after \; in algorithm2e

1 Answers1