定位方程式编号不起作用

Question

在这个例子中，方程编号甚至低于方程本身。
我以为[t]选项[m/c]可以定位数字。没有用。

我怎样才能使方程式编号位于顶部、居中、底部？

\documentclass{article}

\usepackage{showframe}   %% just for demo
\usepackage{mathtools}
\usepackage{amssymb}
\usepackage{amsfonts}
\usepackage{amsthm}
\usepackage{mathtools}
\usepackage{relsize}
\usepackage{stmaryrd}
\usepackage{bm}

\newcommand{\h}[1]{\widehat{\bm{#1}}}

\begin{document}

\begin{align}
\begin{aligned}[t]
\hspace{3cm} R(\alpha \h{a})    &\hspace{1cm}  \longmapsto  \hspace{1cm}  a.
\intertext{Note the special cases for the identity and the $\pi$-rotation:}
\mbox{Identity}    &\hspace{1cm}   \longmapsto     \hspace{1cm}  1         \equiv  -1 \\
\mbox{$L_a$}       &\hspace{1cm}    \longmapsto    \hspace{1cm}  a   \equiv  - a.
\end{aligned}
\end{align}

\begin{equation}
\begin{split}
\hspace{3cm} R(\alpha \h{a})    &\hspace{1cm}  \longmapsto  \hspace{1cm}  a.
\intertext{Note the special cases for the identity and the $\pi$-rotation:}
\mbox{Identity}    &\hspace{1cm}   \longmapsto     \hspace{1cm}  1         \equiv  -1 \\
\mbox{$L_a$}       &\hspace{1cm}    \longmapsto    \hspace{1cm}  a   \equiv  - a.
\end{split}
\end{equation}

\end{document}

Answer 1

这是一个解决方案，其中所有内容都是对齐的，并且整个集合的一个方程编号与任何方程线放在一起，甚至与文本放在一起（在后一种情况下使用环境flalign和\rlap命令进行模拟）：

\documentclass{article}

\usepackage[nomarginpar, showframe]{geometry} %% just for demo
\usepackage{mathtools}
\usepackage{amssymb}
\usepackage{amsfonts}
\usepackage{amsthm}
\usepackage{stmaryrd}
\usepackage{bm}

\newcommand{\h}[1]{\widehat{\bm{#1}}}

\begin{document}

\begin{align}
  \hspace{3cm} R(\alpha \h{a}) &\hspace{1cm} \longmapsto \hspace{1cm} a.\\
\intertext{\rlap{Note the special cases for the identity and the $\pi$-rotation:}}
\mbox{Identity} &\hspace{1cm} \longmapsto \hspace{1cm} 1 \equiv -1\notag\\
  L_a &\hspace{1cm} \longmapsto \hspace{1cm} a \equiv - a. \notag
\end{align}


\begin{align}
  \hspace{3cm} R(\alpha \h{a}) &\hspace{1cm} \longmapsto \hspace{1cm} a. \notag\\
\intertext{\rlap{Note the special cases for the identity and the $\pi$-rotation:}}
\mbox{Identity} &\hspace{1cm} \longmapsto \hspace{1cm} 1 \equiv -1\\
  L_a &\hspace{1cm} \longmapsto \hspace{1cm} a \equiv - a. \notag
\end{align}

 \begin{align}
  \hspace{3cm} R(\alpha \h{a}) &\hspace{1cm} \longmapsto \hspace{1cm} a. \notag \\
\intertext{\rlap{Note the special cases for the identity and the $\pi$-rotation:}}
\mbox{Identity} &\hspace{1cm} \longmapsto \hspace{1cm} 1 \equiv -1 \notag \\
  L_a &\hspace{1cm} \longmapsto \hspace{1cm} a \equiv - a.
\end{align}

\begin{flalign}
  & & \hspace{3cm} R(\alpha \h{a}) &\hspace{1cm} \longmapsto \hspace{1cm} a. & & \notag\\[8pt]
 & \text{\rlap{Note the special cases for the identity and the $\pi$-rotation:}} \\[8pt]
 & & \mbox{Identity} &\hspace{1cm} \longmapsto \hspace{1cm} 1 \equiv -1 \notag\\
  & & L_a &\hspace{1cm} \longmapsto \hspace{1cm} a \equiv - a. \notag
\end{flalign}

\end{document}