Adding a caption to an equation in LaTeX

Question

Well, it seems simple enough, but I can't find a way to add a caption to an equation. The caption is needed to explain the variables used in the equation, so some kind of table-like structure to keep it all aligned and pretty would be great.

Answer 1

You may want to look at http://tug.ctan.org/tex-archive/macros/latex/contrib/float/ which allows you to define new floats using \newfloat

I say this because captions are usually applied to floats.

Straight ahead equations (those written with $ ... $, $$ ... $$, begin{equation}...) are in-line objects that do not support \caption.

Answer 2

The \caption command is restricted to floats: you will need to place the equation in a figure or table environment (or a new kind of floating environment). For example:

\begin{figure}
\[ e = m c^2 \]
\caption{A famous equation}
\end{figure}

The point of floats is that you let LaTeX determine their placement. If you want to equation to appear in a fixed position, don't use a float. The \captionof command of the caption package can be used to place a caption outside of a floating environment. It is used like this:

\[ e = m c^2 \]
\captionof{figure}{A famous equation}

This will also produce an entry for the \listoffigures, if your document has one.

To align parts of an equation, take a look at the eqnarray environment, or some of the environments of the amsmath package: align, gather, multiline,...