\label{key}
A \label
command appearing in ordinary text assigns to the
key
the
number of the current sectional unit; one appearing inside a numbered
environment assigns that number to the key
.
A key
can consist of any sequence of letters, digits, or punctuation
characters. Upper- and lowercase letters are different.
The number assigned to the key can be accessed by use of the
\ref
command. For example,
\begin{equation} .... .... \label{eq:no1} \end{equation} ... One can see from Eq.~(\ref{eq:no1}) that ...
In a table or figure
environment, the \label
command should follow the
\caption
command (or be part of its
argument) since it is the \caption
command which generates the
number.
The \label
command is fragile but it
can be used in the argument of a
sectioning command or
\caption
command.