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The following aligned equation gives an error 'Extra }, or forgotten \right.':

\begin{equation}
\begin{aligned}
U&=\mathbb{R}^{M N}\\
V&=\mathbb{R}^{2 M N}\\
W&=\mathbb{R}^{4 M N}\\
\min_{v\in V} \left\{E_p(v)&=\|\nabla v\|_{W,1}+\lambda \|\rho(v)\|_{U,1} \right\}
\end{aligned}
\end{equation}

Removing the \left and \right commands avoids the error:

\begin{equation}
\begin{aligned}
U&=\mathbb{R}^{M N}\\
V&=\mathbb{R}^{2 M N}\\
W&=\mathbb{R}^{4 M N}\\
\min_{v\in V} \{E_p(v)&=\|\nabla v\|_{W,1}+\lambda \|\rho(v)\|_{U,1} \}
\end{aligned}
\end{equation}

I don't understand why having the alignment marker inside a \left \right command is an error. How do I align an equation with the alignment inside a \left \right command?

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marked as duplicate by Werner, karlkoeller, Harish Kumar, Adam Liter, Jesse Mar 14 at 5:52

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

2  
It's just not possible (see Using \left( & \right) around amsmath's align delimiter (“&”)). You can get around it though, either by using \big-like delimiters, or following the guidelines in Left/Right across multiline equation. –  Werner Mar 14 at 5:34

1 Answer 1

up vote 1 down vote accepted

You need to close the \left before the alignment with \right. and open another \left:

enter image description here

But this may be problematic if there are different vertical sizes on either side. In this case the easier solution is to use the fixed size delimiters such as \big, \Big, etc.

Code:

\documentclass{article}
\usepackage{amsmath,amssymb}

\begin{document}
\begin{equation}
\begin{aligned}
U&=\mathbb{R}^{M N}\\
V&=\mathbb{R}^{2 M N}\\
W&=\mathbb{R}^{4 M N}\\
\min_{v\in V} \left\{E_p(v)\right.&=\left.\|\nabla v\|_{W,1}+\lambda \|\rho(v)\|_{U,1} \right\}
\end{aligned}
\end{equation}
\end{document}
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