label \theequation inside math

Question

Code:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\begin{document}
    \begin{align*}
        J
        &= J_0 + 2 m r^2 
        & \label{eq:asdf}\refstepcounter{equation}(\theequation) 
        && \tilde{J} 
        &= J_0 + 2 m \tilde{r}^2 & \refstepcounter{equation}(\theequation)
    \end{align*}
    \eqref{eq:asdf}
\end{document}

Output: outputOfCode

I want to reference (1).

You need to put \label after \refstepcounter (although using align* and then using \refstepcounter by hand is pretty odd:-) — David Carlisle, Oct 03 '14 at 14:51
Try running it twice. The first run writes the aux file, the second reads it. — John Kormylo, Oct 03 '14 at 14:53
May be of interest: http://tex.stackexchange.com/a/42728/2417 — Ian Thompson, Oct 03 '14 at 14:58
@DavidCarlisle: equation counter is set to 0 before I call \label. That means that there has to appear a (0). If that were true, I would be happy. — Michael Banucu, Oct 03 '14 at 14:58
The aux file contains only \relax. \label isn't writing anything. — John Kormylo, Oct 03 '14 at 15:07
@MichaelBanucu the value of the counter is irrelevant what matters is the current referencerable value and that is empty until there has been a refstepcounter. try putting \section{foo} before your equation and you will see the \ref picks up the section number. The usage above is exactly like putting \lable before \caption in a figure, about which there are several answers on this site and elsewhere — David Carlisle, Oct 03 '14 at 15:22
@JohnKormylo: \relax is not working or I don't know how to use it. — Michael Banucu, Oct 03 '14 at 15:26
ah in addition to coming after refstepcounter you need to undo amsmath's redefintion — David Carlisle, Oct 03 '14 at 15:26
@DavidCarlisle: How do I undo amsmath's redefinition? What is amsmath's redefinition? Where can I find out what is amsmaths's redefinition? I think that I have to set the "current label". I think that's what \section and align are doing. But how do I set the current label? — Michael Banucu, Oct 03 '14 at 15:29
\refstepcounter sets the current label (which is why you need to do that first, as for undoing amsmath definition John beat me by a few seconds:-) — David Carlisle, Oct 03 '14 at 15:32

score 4 · Accepted Answer · answered Oct 03 '14 at 15:30

4

Amsmath sets \let\label=\@gobble in align*.

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\begin{document}
\let\goodlabel=\label
    \begin{align*}
        J
        &= J_0 + 2 m r^2 
        & \refstepcounter{equation}\goodlabel{eq:asdf}(\theequation)
        && \tilde{J} 
        &= J_0 + 2 m \tilde{r}^2 & \refstepcounter{equation}(\theequation)
    \end{align*}
    \eqref{eq:asdf}
\end{document}

gobble

answered Oct 03 '14 at 15:30

John Kormylo

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Ohh you beat me by 10 sec:-) – David Carlisle Oct 03 '14 at 15:31
@David Carlisle - If it makes you feel any better, it took longer than that to crop the image. – John Kormylo Oct 03 '14 at 15:36
@JohnKormylo: what is @gobble? – Michael Banucu Oct 03 '14 at 15:45
@Michael Banucu - I've seen it before but never seen the \def. I've always assumed from context that it eats arguments, but otherwise does nothing (like \relax). – John Kormylo Oct 04 '14 at 04:00

label \theequation inside math

1 Answers1