Take the 2-minute tour ×
TeX - LaTeX Stack Exchange is a question and answer site for users of TeX, LaTeX, ConTeXt, and related typesetting systems. It's 100% free, no registration required.

I'm wondering if there's a way to reference the section that an equation is in.

\documentclass{article}
\begin{document}
\section{section 1}\label{sec:first}
\begin{equation}\label{eq:eq1}
    1+1=2 \\
\end{equation}

\section{section2}\label{sec:second}
From equation \eqref{eq:eq1} in section \ref{sec:first}...
\end{document}

Basically, I'd like to replace \ref{sec:first} with a reference to the equation and get the section that it's in. Thank you in advance!

share|improve this question

2 Answers 2

up vote 8 down vote accepted

Probably you want to add the number of the section to the equation number.

In this way every reference to an equation contains also the section number and you don't have to add things like \ref{sec:first}.

You just have to add this line in your preamble:

\numberwithin{equation}{section}

MWE:

\documentclass{article}
\usepackage{amsmath}
\numberwithin{equation}{section}

\begin{document}
\section{section 1}\label{sec:first}
\begin{equation}\label{eq:eq1}
    1+1=2 \\
\end{equation}

\section{section2}\label{sec:second}
\begin{equation}\label{eq:eq2}
    2+2=4 \\
\end{equation}

From equation \eqref{eq:eq1}...
\end{document} 

Output:

enter image description here

share|improve this answer

If you want to have the section number of a reference, you have to use tricks, e.g. the zref package. There is already a solution to a similar question Extract Section number from Equation reference, however, so the merits should go to Werner ;-)

My version sets a special label using zref capabilities, however, you have to use \label{eq:eq1} and \localspeciallabel{eq:eq1} both, but I wrapped it into a common \commonlabel{eq:eq1} command.

The reference to the section is done with \eqsecref{eq:eq1} etc. I changed the name from \eqref, since there is already a command with that name in amsmath package.

\documentclass{article}
\usepackage{zref}

\makeatletter
\zref@newlist{specialreflist}
\zref@newprop{section}{\arabic{section}}
\zref@addprop{specialreflist}{section}
\newcommand*{\localspeciallabel}[1]{\zref@labelbylist{#1}{specialreflist}}%

\newcommand*{\eqsecref}[1]{%
% Do formatting of number here or outside
\zref@extractdefault{#1}{section}{??}
}%
\makeatother


\newcommand{\commonlabel}[1]{%
\label{#1}%
\localspeciallabel{#1}%
}%

\begin{document}


\section{section 1}\label{sec:first}

\section{section2}\label{sec:second}
\begin{equation}\commonlabel{eq:eq1}
    1+1=2 \\
\end{equation}



\section{section 3}%\label{sec:three}

\begin{equation}\commonlabel{eq:eq2}
    \sqrt{2} \approx 1.414 \\
\end{equation}

From equation \ref{eq:eq1} in section \eqsecref{eq:eq1} it is clear that\ldots, whereas equation \ref{eq:eq2} in section \eqsecref{eq:eq2} shows that\ldots

\end{document}

enter image description here

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.