Suppress equation number when not refered to

Question

Is is possible to use only equation or align environments without the * and then automatically suppress the equation number if there is nothing refering to that equation? It would make the LaTeX-life much easier I think.

See also http://tex.stackexchange.com/questions/4728/how-do-i-number-equations-only-if-they-are-referred-to-in-the-text — Lev Bishop, Apr 14 '11 at 14:12

score 13 · Accepted Answer · answered Apr 14 '11 at 13:25

13

see package mathtools and section "3.2.2 Showing only referenced tags". You'll get the documentation by running texdoc mathtools or run texdoctk if you run Linux

answered Apr 14 '11 at 13:25

score 3 · Answer 2 · answered Apr 14 '11 at 13:33

I coded up a workaround before I noticed Herbert's answer. Here it is anyway:

\documentclass{article}
% TEX.SE \url{http://tex.stackexchange.com/q/15820/1402}
\usepackage{amsmath}
\usepackage{etoolbox}

\makeatletter
\appto{\equation}{%
  \notag
  \preto{\label}{%
    \refstepcounter{equation}
    \tag{\arabic{equation}}%
  }
}
\makeatother

\begin{document}

\begin{equation}
A = A
\end{equation}

\begin{equation}\label{B}
B = B
\end{equation}

\begin{equation}
C = C
\end{equation}

Proof: See Equation~\ref{B}.

\end{document}

It's my first use of the etoolbox macros to prepend and append code to hooks. This method first appends \notag to every equation beginning, thus suppressing equation numbering; then prepends to \label the code which steps the counter and resets the tag.

Suppress equation number when not refered to

2 Answers2

Linked