# custom automatic equation numbering

I just read a book where the equations in the Introduction were numbered slightly differently compared to the other sections, namely by (In.x) where x stands for the number (so it starts off as (In.1), (In.2), (In.3) and so on.

I'd like to try this this but I haven't found out so far how to do this systematically, i.e. not tagging each equation manually but rather using someting like the \label functionality .. any suggestions?

You can do this using

\renewcommand{\theequation}{ln.\arabic{equation}}


If you want to switch it back, you can use

\renewcommand{\theequation}{\arabic{equation}}


A complete MWE follows.

\documentclass{article}

\renewcommand{\theequation}{ln.\arabic{equation}}
\begin{document}

$$y=mx+b$$
\end{document}

• there must be a duplicate somewhere (I did search)... if someone points it out, I'll delete my answer... – cmhughes Jan 1 '13 at 20:20

Another possibility is to load mathtools (an extension of amsmath, so it's needless to load the latter), which allows for defining tag ‘styles’ (named tag forms)and use them with a \usetagform command. The previous code would become:

\documentclass{article}
\usepackage{mathtools}

\newtagform{(L}{(ln})

\begin{document}

\usetagform{L}
$$y=mx+b$$

\end{document}