127

I am using align*, but I still need an equation number. I know one solution is to use align and add \nonumber to all lines but the last. Is there a 'lazy' way to do it?

I searched a little and found similar ones suggesting use split: Show equation number only once in align environment

Unfortunately, due to the page break issue I have, I need to use align, because split won't auto page break, as described in Long equation does not page break.

148

Use \tag:

\documentclass{article}
\usepackage{amsmath}
\newcommand\numberthis{\addtocounter{equation}{1}\tag{\theequation}}
\begin{document}
\begin{align*}
a &=b \\
  &=c \numberthis \label{eqn}
\end{align*}
Equation \eqref{eqn} shows that $a=c$.
\begin{equation}
d = e
\end{equation}
\end{document}

See page 3 of the amsmath package documentation for details.

  • Why didn't you use \stepcounter or \refstepcounter instead of \addtocounter? – kiss my armpit Aug 31 '13 at 6:14
  • @PSTikZ --- \refstepcounter isn't needed, as the \ref value is set correctly already. \stepcounter is probably the best choice, to take care of subsidiary counters. I don't think I gave much thought to this when I composed the answer. – Ian Thompson Sep 2 '13 at 8:25
  • Your example works perfectly for me, thank you. I have a followup question though. How can I make the number on the same line than the last line of the euqation provided that the last line is longer normal align would allow (it does fit in align* though) – magu_ Mar 24 '14 at 9:56
  • 1
    @magu_ Please post a new question with an example showing exactly what you want. I think I understand your question, but I'm not 100% sure. Also, other users (who may have better solutions than me) will see the new question, whereas they are unlikely to see new comments here. – Ian Thompson Mar 24 '14 at 12:04
  • 1
    This solution has a problem when combined with the cleveref package: The sorting of \numberthis-references does not work properly. See this question for further detail. If anyone knows a solution fixing this problem, please let me know. – Lukas Sep 30 '16 at 15:32
33

Another option is to use align, and then use \nonumber, as mentioned in http://mirrors.dotsrc.org/ctan/info/math/voss/mathmode/Mathmode.pdf.

Example:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{align}
a &=b \nonumber \\
b &=c
\label{eq:test}
\end{align}
Equation \eqref{eq:test} shows that $a=c$.
\end{document}
  • 5
    The user seems to want to use an align* environment, though. Your approach would involve a lot of \nonumber, if the align contains a lot of lines. – jub0bs Feb 26 '14 at 9:50
  • 7
    Welcome to TeX.SX! This answer, while technically correct, is already mentioned in the second sentence of the question; the asker is looking for a different solution. – ChrisS Feb 26 '14 at 9:51
  • I must have misread the question. I did not see that. Sorry. – martinweiss Feb 27 '14 at 13:03
16

Here are minimal working examples that I use. This is what I have as a header

\documentclass[12pt]{amsart}           
\usepackage{amsmath,amsfonts,amssymb}

Two equations each with separate equation numbers and separate reference labels

\begin{align}
        \dot{a} &  =2\alpha(t)\eta\label{classicalmotion1}\\
        \dot{\eta} &  =-2\gamma(t)a\label{classicalmotion2}%
\end{align}%

Two equations with a single equation number and a single reference label

\begin{equation}
        \begin{aligned}[b]
        \dot{A} &  =2i\alpha(t)B\\
        \dot{B} &  =2i\gamma(t)A
        \end{aligned}
\label{eqn2.qo}
\end{equation}

I am guessing you know how to do the one without equation numbers.

  • thanks! somewhat surprisingly putting the \label(eqn2.qo} before \begin{aligned} changed the position of the eqn number in my case... – Xi'an Oct 26 '14 at 16:38
  • @Xi'an -- putting the \label before the align might change the position of the equation number, but it will also give an incorrect value with \eqref. – barbara beeton Jul 13 '17 at 1:50
0

Another solution.

\begin{subequations}\label{eqn}
\begin{align*}
a &=b \\
  &=c \tag{\ref{eqn}} 
\end{align*}
\end{subequations}
  • Try having two equations like that, you will see that this code doesn't work. – user156344 Apr 5 at 13:44
  • @user156344: tried and it works as well (of course your need to change the equation labels). – user2477759 Sep 10 at 13:58

protected by jub0bs Feb 26 '14 at 9:51

Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).

Would you like to answer one of these unanswered questions instead?

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