Unwanted space when using align and cases

Question

What I want, with manual alignment:

\begin{equation*}
\begin{cases}
    \ang{\varphi} \rightarrow \Omega_n\\
    \varphi^k \hspace{4.4pt}\mapsto \xi_n^k
\end{cases}
\end{equation*}

With align I get unwanted space:

\begin{align*}
\begin{cases}
    \ang{\varphi} &\rightarrow \Omega_n\\
    \varphi^k &\mapsto \xi_n^k
\end{cases}
\end{align*}

You're misusing cases which is not for aligning at relation signs, but for aligning conditions — egreg, Jun 07 '21 at 16:10

score 3 · Accepted Answer · answered Jun 07 '21 at 16:17

You should consider using aligned:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
Original:
[
  \begin{cases}
    \langle\varphi\rangle \rightarrow \Omega_n\
    \varphi^k \hspace{4.4pt}\mapsto \xi_n^k
  \end{cases}
]
Updated:
[
  \left{\begin{aligned}
    \langle\varphi\rangle &\rightarrow \Omega_n\
    \varphi^k             &\mapsto \xi_n^k
  \end{aligned}\right.\kern-\nulldelimiterspace
]
\end{document}

You can also use array, but would have to adjust for the vertical spacing via \arraystretch.

Unwanted space when using align and cases

1 Answers1