4

When using the \labelrel command (with \overset instead of \stackrel as \stackrel is obsolete: Differences between \stackrel and \stackbin) from @Circumscribe Put reference above equal sign and refer to it in an align-environment the alignment is not correct:

\documentclass{article}
\usepackage{mathtools}

\newcounter{relctr} %% <- counter for relations
\renewcommand*\therelctr{\alph{relctr}} %% <- label format

\newcommand\labelrel[2]{%
  \begingroup
    \refstepcounter{relctr}%
    \overset{\textnormal{(\alph{relctr})}}{\mathstrut{#1}}%
    \originallabel{#2}%
  \endgroup
}
\AtBeginDocument{\let\originallabel\label} %% <- store original definition

\begin{document}

\begin{align*}
    a &= b \\
      &\labelrel{=}{someLabel} c
\end{align*}

\end{document}

Misaligned equal sign

This seems to be a well known problem with the \overset command: \overset and align environment: how to get correct alignment? where the aligned-overset package offers a nice solution.

So my question is how one can achieve similar behavior for the \labelrel command or even more generally specify the behavior with align for new commands.

I don't have any experience with coding new commands myself but I decided to post this as a new questions as this may be an interesting question for other users as well.

Here is what I tried:

  • Search the internet

  • Try using the aligned-overset in the definition of \labelrel but I had no idea on how to pass the & from align to the definition

  • Look at the implementation of aligned-overset to copy the relevant code however I almost didn't understand anything.

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1
  • Welcome to TeX.SE! Commented 2 days ago

2 Answers 2

Reset to default
3

Use

\NewDocumentCommand{\labelrel} { m m }{%
  \mathrel{%
    \refstepcounter{relctr}%
    \overset{\mathclap{\textnormal{\therelctr}}}{\mathstrut{#1}}%
    }%
  \originallabel{#2}%
}

with

  • \mathrel such as the space around the command is set for binary relations;
  • \mathclap to remove the space added by the label;
  • {#1} to remove the space added by = with its surrounding.

Example:

\documentclass{article}
\usepackage{mathtools}

\newcounter{relctr} %% <- counter for relations
\renewcommand*\therelctr{(\alph{relctr})} %% <- label format

\NewDocumentCommand{\labelrel} { m m }{%
  \mathrel{%
    \refstepcounter{relctr}%
    \overset{\mathclap{\textnormal{\therelctr}}}{\mathstrut{#1}}%
    }%
  \originallabel{#2}%
}

\AtBeginDocument{\let\originallabel\label}

\begin{document}

\begin{align*}
    a &= b \\
      &\labelrel{=}{someLabel} c
\end{align*}

\begin{align*}
    a &= b \\
      &\labelrel{=}{someOtherLabel} c
\end{align*}

See \ref{someLabel} and \ref{someOtherLabel}.

\end{document}

Example

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11
  • It works great if I only have one \labelrel in an align environment. However when adding a second I get the error: "Package amsmath Error: Multiple \label's: label 'someLabel' will be lost." Commented 2 days ago
  • Furthermore the referencing doesn't work. So I get the warning: "LaTeX Warning: Reference `someLabel' on page 1 undefined" Commented 2 days ago
  • 1
    @GreyEminence It seems to work with \originallabel, as in the answer you linked (I removed it because I didn't see why we need it; note that I also removed \begingroup...\endgroup because I don't understand why it is relevant, but maybe I'm also wrong). Commented 2 days ago
  • 1
    you should probably put the refstepcounter inside the mathrel Commented 2 days ago
  • 1
    @jlab it is. it's only needed with hyperref or similar which causes refstepcounter to make a link anchor which would affect the spacing Commented yesterday
3

There's no need to define \originallabel, because amsmath provides \ltx@label for the same purpose.

However, you need to make \mathstrut into a \mathrel, so \overset can make the object as a relation as well.

\documentclass{article}
\usepackage{mathtools}

\newcounter{relctr} %% <- counter for relations
\renewcommand*\therelctr{\alph{relctr}} %% <- label format

\makeatletter
\newcommand\labelrel[2]{%
  \refstepcounter{relctr}%
  \overset{\makebox[0pt]{\normalfont\scriptsize(\therelctr)}}
    {\mathrel{\mathstrut}#1}%
  \ltx@label{#2}%
}
\makeatother

\begin{document}

\begin{align*}
    a &= b \\
      &\labelrel{=}{someLabel} c
\end{align*}

The ref: \ref{someLabel}

\end{document}

output

(Note: the picture has been made with twocolumn to reduce the size.)

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