# An embarrassing Multline error [duplicate]

Here I am, trying to display an equation that takes way too long for one line, so I called multline.

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{geometry}
\usepackage{amssymb,amsmath}
\usepackage{amsfonts}
\geometry{a4paper}
\begin{document}
\begin{multline}
S_E=\int \mathrm{d}t \left[\frac{(f'\dot{\xi})^2}{2} \int \mathrm{d}x(\phi_0+1)^2+\frac{f^2}{2}\int \mathrm{d}x \phi'^2\\
+ \int \mathrm{d}x (\psi^2-1)^2(\psi^2-\delta_1)
+ \frac{1}{\gamma+\psi^2}\left[\left(f^2(\phi_0^2+1)-2f(\phi_0+1)\right)^2-\frac{\delta_2{4}(f(\phi_0+1)-3)(f(\phi_0+1))^2\right]\right] \\
\label{actionrescale}
\end{multline}
\end{document}


However, if I called $$and$$ instead of \begin{multline}$$and$$\end{multline} the equation would show up just fine (or at least as much of it that could fit on the resulting pdf file). What exactly is wrong with this document?

## marked as duplicate by Torbjørn T., Mico, Masroor, Thorsten, GuidoJul 5 '14 at 6:25

• Welcome to TeX.SX! You can't split \left[ ... \right] over multiple lines, use e.g. \biggl[ and \biggr] instead. – Torbjørn T. Jul 4 '14 at 21:57

Here is a solution. I split it differently, and define a differential operator \d that has a correct spacing (it comes from one answer here, but I don't know where).

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{geometry}
\usepackage{amssymb,amsmath}
\usepackage{amsfonts}
\geometry{a4paper}

\renewcommand*{\d}{\mathop{}\mathopen{}\mathrm{d}}

\begin{document}

\begin{multline}
\label{actionrescale}
S_E=\int \d t \biggl[\frac{(f'\dot{\xi})^2}{2} \int (\phi_0+1)^2 \d x + \frac{f^2}{2}\int \phi'^2 \d x
+ \int (\psi^2-1)^2(\psi^2-\delta_1)\d x  \\
+ \frac{1}{\gamma+\psi^2}\Bigl[\left(f^2(\phi_0^2 + 1)-2f(\phi_0 + 1)\right)^2 -
\frac{\delta_2}{4}\bigl(f(\phi_0 + 1)-3\bigr)\bigl(f(\phi_0 + 1)\bigr)^2\Bigr]\biggr]
\end{multline}

\end{document}


• There is no need for \biggr. and \biggl.. – Torbjørn T. Jul 5 '14 at 5:11
• @Torbjørn T:: I need them not to have two consecutive ] at the end of the formula, thus improving legibility. I might as well have used two pairs \left - right. – Bernard Jul 5 '14 at 9:00
• Huh? Unlike \left\right there is AFAIK no requirement to 'end' a \biggl with a corresponding \biggr. As far as I can see, the \biggr. and \biggl. do just about nothing. – Torbjørn T. Jul 5 '14 at 10:46
• @Torbjørn T: You're right. I added those \biggr/l. because I mixed up on trying various solutions: it happened that I had a blank line and of course an error message, and thought I had to add those \biggl/r. I'll modify my answer at once. Thanks for pointing me this. – Bernard Jul 5 '14 at 12:06