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!

score 66 · Answer 1 · edited Jul 15 '17 at 14:54

66

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.

edited Jul 15 '17 at 14:54

David Carlisle

757,742

answered Jun 28 '11 at 15:04

egreg

1,121,712

1

your advice works with both (eqnarray and align) but from now on I'll use align – Bruce_Warrior Jun 28 '11 at 15:10
@Bruce_Warrior, exactly. This method works just fine in align and its derivatives (align*, aligned, etc) just fine. – Alfredo Hernández Feb 25 '15 at 23:15
1

But what if the math is at the bottom of one page and the \footnotetext{text of the footnote} is forced to a second page because of lack of space? Won't that lead to the strange result of showing the actual footnote on a different page than the footnote mark? – L. F. Sep 24 '18 at 04:34
2

@L.F. Yes, that's a risk when using this. I recommend never footnoting math. – egreg Sep 24 '18 at 08:22

score 39 · Answer 2 · edited Jul 15 '17 at 14:54

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}

I do that but the firts footnotemark redirect me to first page and the second footnote works fine redirect me to the localization of the second footnote. Do you know why this happen to me? — Bruce_Warrior, Jun 28 '11 at 15:24

score 21 · Answer 3 · edited Apr 13 '17 at 12:34

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}}}

Footnote in math mode

3 Answers3

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