Footnote in math mode

Question

How can I insert a footnote into math mode? I tried this (with required packages)

\usepackage{amsmath}
\usepackage{hyperref}
\usepackage{ccaption}

And i.e if I try

\begin{eqnarray}
foo && foo \text{\footnote{something}}\\
foo && foo \mbox{\footnote{something else}}
\end{eqnarray}

the link to the footnote appears, but not in the footnote position and if I click it I'm redirected to the first page. If I am in text mode I don't have this problem. How can I do this? Thanks in advance!

Answer 1

You shouldn't be using eqnarray, first of all, but rather align.

\begin{align}
a &= b && \text{something\footnotemark} \\
c &= d && \text{other}
\end{align}
\footnotetext{text of the footnote}

While \footnote works in equation, it doesn't in other alignment environments.

Answer 2

According to Kopka and Daly, A Guide to LaTeX, p. 96--97, the \footnote command is not allowed in math mode, so you'll have to resort to using \footnotemark inside math environments and \footnotetext{<Some text>} in normal text mode.

Note that if, as in your example, more than one footnote is needed, you have to adjust the footnote counter by subtracting n-1 (n being the number of footnotes in math mode) before the first \footnotetext and using \stepcounter before all other occurences of \footnotetext.

\documentclass{article}

\begin{document}

\begin{eqnarray}
foo && foo \footnotemark\\
foo && foo \footnotemark
\end{eqnarray}

\addtocounter{footnote}{-1}
\footnotetext{something}
\stepcounter{footnote}
\footnotetext{something else}

\end{document}

Answer 3

If you want to put footnotes in equation environment, just use \footnote in math mode:

\begin{equation}
foo\footnote{bar}
\end{equation}

For eqnarray environment or some other complex environments, use:

\begin{eqnarray}
foo\footnotemark
\end{eqnarray}
\footnotetext{bar}

(Well, eqnarray is wicked, see eqnarray vs align)

---

However, it is not a good manner to use footnotes in math equations. The default marks could be considered as exponents. If it is really necessary, it is better to redefine \thefootnote to get a different mark style. For example:

% symbol sequence: * \dagger \ddagger \S \P ...
\renewcommand\thefootnote{\fnsymbol{footnote}}

or

% circled number: ①②③④⑤⑥⑦⑧⑨
\usepackage{pifont}
\renewcommand\thefootnote{\ding{\numexpr171+\value{footnote}}}