General ⇒ Single equation number in multi-line equation

[Steztric]

Hey people;

I have a very wide equation that I can't put on one line. If I do, it runs off the end of the page.

Unfortunately, when I use the newline character \\ to put part of the equation on the next line, the eqnarray environment thinks it is another equation and gives a separate equation number to it. It is only supposed to be one equation!

This is the code;

Code: Select all

\begin{eqnarray}
\frac{dP\left(z\right)}{dX} =&re^{-r\left(T-z\right)}\frac{C/{NE}}{1-e^{-rT}} + \frac{1}{E}\int\limits_z^T \frac{dv}{dR}\frac{dR}{dt}e^{-r\left(t-z\right)}dt \\
&-\frac{v\left(\overline{R}\right)}{E}e^{-r\left(T-z\right)} + re^{-r\left(T-z\right)}\frac{\frac{1}{E}\int\limits_0^T ve^{-ru}du}{1-e^{-rT}}
\label{eq:eight}
\end{eqnarray}

Any ideas?

Thanks

[UJS]

If you use \nonumber before a line break, that line won't get an equation number.

[gmedina]

Hi,

to get a centered number, you can use a combination of the align and split environments provided by amsmath, as the following example suggests:

Code: Select all

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{align}
  \label{eq:eight}
  \begin{split}
    \frac{dP\left(z\right)}{dX} =\ &re^{-r\left(T-z\right)}\frac{C/{NE}}{1-e^{-rT}} + \frac{1}{E}\int\limits_z^T \frac{dv}{dR}\frac{dR}{dt}e^{-r\left(t-z\right)}dt \\
    &-\frac{v\left(\overline{R}\right)}{E}e^{-r\left(T-z\right)} + re^{-r\left(T-z\right)}\frac{\frac{1}{E}\int\limits_0^T ve^{-ru}du}{1-e^{-rT}}
  \end{split}
\end{align}

\end{document}

By the way, you shouldn't use eqnarray anymore. Reasons can be found in l2tabu and in Avoid eqnarray!

The mathmode document contains useful information about typesetting math.