Cross-referencing displayed equations

Authors will probably not cross-reference every equation in text. When a numbered equation needs to be referred to in text by its number, the \label{tag} and \ref{tag} commands should be used. The \label command is used within the equation or the eqnarray line to be referenced:

\begin{equation}
A=B \label{pauli}
\end{equation}
... It follows from Eq.\ (\ref{pauli})
that this is the case ...

Please note the parentheses surrounding the command. They are necessary for proper output. You can also label individual lines in an eqnarray. Numbers produced with \eqnum can also be cross-referenced: just follow the \eqnum command with a \label command. Please see Sec. for further information about cross-referencing.