[Tex/LaTex] Using \left( & \right) around amsmath’s align delimiter (“&”)

alignamsmathdelimiters

I want to align equations (using the align environment from the amsmath package) inside matching \left( and \right) commands. For example:

\documentclass[a4paper,12pt]{article}

\usepackage{amsmath}

\begin{document}

\begin{align}
    a \left( b &= c \right)\\
    d \left( e &= f \right)
\end{align}

\end{document}

But that code gives this error:

Extra }, or forgotten \right.

The error disappears when I remove the delimiters. Is there a workaround for this?

Best Answer

You cannot split \left...\right across alignment tabs. One solution is to use the \big-delimiters (which don't require pairwise usage):

enter image description here

\documentclass{article}
\usepackage{amsmath}% http://ctan.org/pkg/amsmath

\begin{document}

\begin{align}
  a \bigl( b &= c \biggr) \\
  d \Bigl( e &= f \Biggr)
\end{align}

\end{document}

The above example is just to illustrate some delimiter sizes you can choose from. See section 4.14.1 Delimiter sizes of the amsmath user guide for more options:

enter image description here

Alternatively, one can adjust the alignment manually and avoid using & altogether. However, the above option is far easier to manage.

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