Splitting an equation

Question

\documentclass[12pt,a4paper]{thesis}

\usepackage{amsmath}\usepackage{amssymb}
\usepackage{graphicx}

\usepackage[left=1.25in, right=1.0in, top=1.25in, bottom=1.0in]{geometry}

\newcommand{\piRsquare}{\pi r^2}
\begin{document} \baselineskip=22pt

  \begin{equation}
    \begin{split} L(A) = c_{d} \int\limits_{0}^{\infty}  r^{d-1} \left( \frac{1}{2} \dot{A}^{2} \exp\left(-\frac{2 r^{2}}{R^{2}}\right) - \frac{1}{2}A^{2} \left(\frac{4r^{2}}{R^{4}}\right)\exp\left(-\frac{2 r^{2}}{R^{2}}\right)  \\
     &\quad - A^{2} \exp\left(-\frac{2 r^{2}}{R^{2}}\right) + A^{3} \exp\left(-\frac{3 r^{2}}{R^{2}}\right) - \frac{1}{4} A^{4} \exp\left(-\frac{4 r^{2}}{R^{2}}\right) \right) dr,
    \end{split}
    \end{equation}
\end{document}

In the above equation, where have I done wrong?

You're trying to split a \left...\right pair across multiple lines, which is not possible without some trickery. See Left/Right across multiline equation. — Werner, Sep 01 '13 at 06:29

score 3 · Answer 1 · edited Jun 04 '17 at 19:37

As with Left/Right across multi-line equation you are attempting to split a \left...\right pair across a multi-line equation. Since you don't have variable-sized content across the lines, a simple right....\left. pair across the break works.

Below I've highlighted the structure to show corresponding \left...\right pairs.

enter image description here

\documentclass{article}
\usepackage{amsmath}% http://ctan.org/pkg/amsmath
\begin{document}
\begin{align*}
  L(A) &= c_{d} \int_0^\infty r^{d-1}
    \left(
      \frac{1}{2} \dot{A}^{2} \exp
      \left(
        -\frac{2 r^{2}}{R^{2}}
      \right)
      -\frac{1}{2}A^{2}
      \left(
        \frac{4r^{2}}{R^{4}}
      \right)
      \exp
      \left(
        -\frac{2 r^{2}}{R^{2}}
      \right)
    \right. \\
    & \qquad 
    \left.
      - A^{2} \exp
      \left(
        -\frac{2 r^{2}}{R^{2}}
      \right)
      + A^{3} \exp
      \left(
        -\frac{3 r^{2}}{R^{2}}
      \right)
      - \frac{1}{4} A^{4} \exp
      \left(
        -\frac{4 r^{2}}{R^{2}}
      \right)
    \right) \mathrm{d}r,
\end{align*}
\end{document}

Another option would be to avoid \left...\right pairs and use \big-like structures:

enter image description here

\documentclass{article}
\usepackage{amsmath}% http://ctan.org/pkg/amsmath
\begin{document}
\begin{align*}
  L(A) &= c_{d} \int_0^\infty r^{d-1}
    \biggl(
      \frac{1}{2} \dot{A}^{2} \exp
      \biggl(
        -\frac{2 r^{2}}{R^{2}}
      \biggr)
      -\frac{1}{2}A^{2}
      \biggl(
        \frac{4r^{2}}{R^{4}}
      \biggr)
      \exp
      \biggl(
        -\frac{2 r^{2}}{R^{2}}
      \biggr)
    \\
    & \qquad 
      - A^{2} \exp
      \biggl(
        -\frac{2 r^{2}}{R^{2}}
      \biggr)
      + A^{3} \exp
      \biggl(
        -\frac{3 r^{2}}{R^{2}}
      \biggr)
      - \frac{1}{4} A^{4} \exp
      \biggl(
        -\frac{4 r^{2}}{R^{2}}
      \biggr)
    \biggr) \mathrm{d}r,
\end{align*}
\end{document}

The advantage from such usage is that it doesn't struggle with multi-line breaking if you have have a \big-left on one line and a \big-right on another.

Mico · Answer 2 · 2017-06-04T19:39:54.650

There are two issues that prevent the equation from being typeset correctly:

One mustn't let \left[ and \right] span an explicit linebreak. To fix this, either provide "dummy" \right. and \left. statements on the first and last lines -- but this risks producing differently-sized "fences" in case the material enclosed by the \left ... \right statements differs in height across the lines -- or use explicit \bigg statements, as is shown in the example below.
You have an alignment symbol, &, on the second line but not on the first. I suggest using something like \qquad\quad after the & symbol on the second line to ensure that the material on the second line starts to the right of the integral symbol on the first line. Alternatively, you could align the first line on \bigg[ instead of on =.

I don't have the thesis document class on my TeX system; I've used article instead in the example below.

enter image description here

\documentclass[12pt,a4paper]{article}
\usepackage{amsmath}
\usepackage[left=1.25in, right=1.0in, top=1.25in, bottom=1.0in]{geometry}
\newcommand{\piRsquare}{\pi r^2}
\begin{document} 
%\baselineskip=22pt
\begin{equation}
\begin{split} L(A) 
&= c_{d} \int\limits_{0}^{\infty}  r^{d-1} \biggl[ 
\frac{1}{2} \dot{A}^{2} \exp\left(-\frac{2 r^{2}}{R^{2}}\right) - 
\frac{1}{2}A^{2} \left(\frac{4r^{2}}{R^{4}}\right) \exp\left(-\frac{2 r^{2}}{R^{2}}\right)  \\
&\qquad\quad % make second line start to right of
             % integral symbol on first line
- A^{2} \exp\left(-\frac{2 r^{2}}{R^{2}}\right) + 
  A^{3} \exp\left(-\frac{3 r^{2}}{R^{2}}\right) - 
\frac{1}{4} A^{4} \exp\left(-\frac{4 r^{2}}{R^{2}}\right) 
\biggr] \,dr,
\end{split}
\end{equation}
\end{document}

score 1 · Accepted Answer · edited Jun 04 '17 at 19:37

\documentclass[12pt,a4paper]{thesis}

\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{graphicx}

\usepackage[left=1.25in, right=1.0in, top=1.25in, bottom=1.0in]{geometry}

\newcommand{\piRsquare}{\pi r^2}
\begin{document} \baselineskip=22pt
    \begin{equation}
        \begin{split} L(A) = c_{d} \int\limits_{0}^{\infty} r^{d-1} \left( \frac{1}{2} \dot{A}^{2} \exp\left(-\frac{2 r^{2}}{R^{2}}\right) - \frac{1}{2}A^{2} \left(\frac{4r^{2}}{R^{4}}\right)\exp\left(-\frac{2 r^{2}}{R^{2}}\right)\right. \\
        \quad \left.- A^{2} \exp\left(-\frac{2 r^{2}}{R^{2}}\right) + A^{3} \exp\left(-\frac{3 r^{2}}{R^{2}}\right) - \frac{1}{4} A^{4} \exp\left(-\frac{4 r^{2}}{R^{2}}\right) \right) dr,
        \end{split}
    \end{equation}
\end{document}

You have imbalanced the \right and \left brackets, note the addition \left. and \right. in the code.

Splitting an equation

3 Answers3