1

I am just wondering if there is a way to refer to autolabelled equations in the text.

I can use:

\begin{equation}
x^2
\end{equation}

The equation will autonumber, but I can't refer to it in the text without providing a label, and I don't want to do that because I might be added other equations before it in the future (plus I'd still have to update the text).

Apologies if this has been asked. I have tried to search for it with no luck. Maybe I am using the wrong search terms.

Phelype Oleinik
  • 70,814
cohara
  • 35

1 Answers1

2

You don't have to number the equations by yourself. Let LaTeX do the heavy lifting. You can just give names to the equations and refer to them by their names:

enter image description here

\documentclass{article}
\usepackage{amsmath}
\begin{document}
Equation~\ref{xsquared} shows that the universe is
infinite, but equation~\ref{ysquared} says otherwise.
\begin{equation}\label{xsquared}
  a = x^2
\end{equation}
\begin{equation}\label{ysquared}
  b = y^2
\end{equation}
\end{document}

If you insert an equation before it, LaTeX will do the numbering by itself:

enter image description here

\documentclass{article}
\usepackage{amsmath}
\begin{document}
Equation~\ref{answer} is the Answer to Life, the Universe and Everything

Equation~\ref{xsquared} shows that the universe is
infinite, but equation~\ref{ysquared} says otherwise.
\begin{equation}\label{answer}
  x = y = 42
\end{equation}
\begin{equation}\label{xsquared}
  a = x^2
\end{equation}
\begin{equation}\label{ysquared}
  b = y^2
\end{equation}
\end{document}

Getting fancy :)

Barbara Beeton pointed a few problems with my previous answer.

An empty line between an \end{equation} and the next \begin{equation} will create an extra empty space between the equations, so I removed them.

Notice also the ugly spacing between equations (1) and (2) in the previous figure. The gather environment from amsmath allows multiple equations inside the same environment and makes the spacing between them correct. At the same time, it allows one label per equation the same way that the three equation environments allowed:

enter image description here

\documentclass{article}
\usepackage{amsmath}
\begin{document}
Equation~\ref{answer} is the Answer to Life, the Universe and Everything

Equation~\ref{xsquared} shows that the universe is
infinite, but equation~\ref{ysquared} says otherwise.
\begin{gather}
  x = y = 42\label{answer}\\
  a = x^2\label{xsquared}\\
  b = y^2\label{ysquared}
\end{gather}
\end{document}

Much better now :)

Phelype Oleinik
  • 70,814
  • 1
    there's an awful lot of space above and between these equations. it's not recommended to leave a blank line above any display, and if multiple equations are grouped with no (or very little) text between them, using a multi-line structure from amsmath is also recommended. (gather would be the most appropriate here.) – barbara beeton Mar 08 '18 at 18:32
  • @barbarabeeton I didn't notice that a blank line above a math display would create those spaces. Thank you for the advice :) – Phelype Oleinik Mar 08 '18 at 22:02
  • Thanks Phelype Oleinik, I guess I was just putting the label in the wrong place – cohara Mar 09 '18 at 14:02