“ERROR: Extra }, or forgotten \right.” in align* enviroment

Why do I get a "ERROR: Extra }, or forgotten \right." in the following align* environment?

\begin{align*}
\int\left[\left(\der{E_z}{y}-\der{E_y}{z}-\mu\der{\alpha}{t}\right)\alpha&+\left(\der{E_x}{z}-\der{E_x}{x}-\mu\der{\beta}{t}\right)\beta\\
&+\left(\der{E_y}{x}-\der{E_x}{y}-\mu\der{\gamma}{t}\right)\gamma\left.\vphantom{\left(\der{E_y}{x}}\right]d\omega=0.
\end{align*}


thanks

This is a case where multline* should be used; in any case you can't have unbalanced \left or \right in one of the lines.

\documentclass{article}
\usepackage{amsmath}
\newcommand{\der}[2]{\frac{\partial #1}{\partial #2}}

\begin{document}
\begin{multline*}
\int\biggl[
\left(\der{E_z}{y}-\der{E_y}{z}-\mu\der{\alpha}{t}\right)\alpha
+\left(\der{E_x}{z}-\der{E_x}{x}-\mu\der{\beta}{t}\right)\beta +{}\\
\left(\der{E_y}{x}-\der{E_x}{y}-\mu\der{\gamma}{t}\right)\gamma
\biggr]\,d\omega=0.
\end{multline*}
\end{document}


(I guessed at the definition of \der.)

• Thanks, but I wanted alignment. (Yes, your guess of \der is right. ☺) – Geremia Oct 10 '13 at 15:10
• @Geremia No, you don't want vertical alignment. ;-) – egreg Oct 10 '13 at 15:43

Every \left needs to be matched with a corresponding \right:

\begin{align*}
\int\left[\left(\der{E_z}{y}-\der{E_y}{z}-\mu\der{\alpha}{t}\right)\alpha\right.&+\left(\der{E_x}{z}-\der{E_x}{x}-\mu\der{\beta}{t}\right)\beta\\
&+\left(\der{E_y}{x}-\der{E_x}{y}-\mu\der{\gamma}{t}\right)\gamma\left.\vphantom{\left(\der{E_y}{x}\right)}\right]d\omega=0.
\end{align*}