同一方程线上的两个标签

Question

我希望在同一行上创建一组紧凑的两个方程式，每个方程式都有标签，两个标签都在最右边。代码如下：

\documentclass{article}
\usepackage{amsmath}
\begin{document}
We have
\begin{equation}
a = b \label{eqab} \quad \text{and} \quad c = d \label{eqcd}
\end{equation}
and equations \ref{eqab} and \ref{eqcd} are nice.
\end{document}

（源代码行内的标签位置无关紧要），并且会出现类似如下的情况：

We have\vspace{3ex}

\hfill $a=b \quad \text{and} \quad c=d$ \hfill (1) and (2)\vspace{3ex}

and equations (1) and (2) are nice.

但是将两个\label放在同一行会导致“Package amsmath 错误：

Multiple \label...` (the same for `\tag`).

Answer 1

也许你正在寻找这样的东西：

\documentclass{article}
\usepackage{amsmath}

\usepackage[a4paper,showframe]{geometry}

\begin{document}
We have:

    \noindent\begin{minipage}{0.4\textwidth}
\begin{equation}
a = b \label{eqab}
\end{equation} 
    \end{minipage}%
    \begin{minipage}{0.2\textwidth}\centering
    and 
    \end{minipage}%
    \begin{minipage}{0.4\textwidth}
\begin{equation}
c = d \label{eqcd}
\end{equation}
    \end{minipage}\vskip1em

Equations \ref{eqab} and \ref{eqcd} are nice. The same is valid for the next two:

\begin{subequations}\label{eq:3}
    \noindent\begin{minipage}{0.4\textwidth}
\begin{equation}
a = b \label{eq:3a}
\end{equation}
    \end{minipage}%
    \begin{minipage}{0.2\textwidth}\centering
    and
    \end{minipage}%
    \begin{minipage}{0.4\textwidth}
\begin{equation}
c = d \label{eq:3b}
\end{equation}
    \end{minipage}\vskip1em
\end{subequations}

which are  \ref{eq:3a} and \ref{eq:3b}.
    \end{document}

Answer 2

\documentclass{article}
\usepackage{amsmath,tabularx}
\begin{document}
We have

\noindent
\begin{tabularx}{\linewidth}{XXX}
\begin{equation}
    a = b \label{eqab}
\end{equation}
& \[ \text{and} \] &
\begin{equation}
    c = d \label{eqcd}
\end{equation}
\end{tabularx}

and equations \ref{eqab} and \ref{eqcd} are nice.
\end{document}

Answer 3

这是预料之中的，因为它不是\label生成方程编号的。

如果您确实希望在同一行上有两个编号方程式（我不鼓励这样做），您可以求助于小页面：

\documentclass{article}
\usepackage{amsmath}
\begin{document}
We have
\begin{center}
\begin{minipage}[b]{.3\textwidth}
\vspace{-\baselineskip}
\begin{equation}
a = b \label{eqab}
\end{equation}
\end{minipage}%
\hfill\hfill and\hfill
\begin{minipage}[b]{.3\textwidth}
\vspace{-\baselineskip}
\begin{equation}
c = d \label{eqcd}
\end{equation}
\end{minipage}
\end{center}
and equations \ref{eqab} and \ref{eqcd} are nice.
\end{document}

Answer 4

Amsmath 可能明确禁止在一个方程中使用多个宏\label，但这并不意味着不能创建另一个宏来执行相同的任务。注意：此版本与 hyperref 不兼容。

\documentclass{report}
\usepackage{amsmath}

\makeatletter
\newcommand{\steplabel}[1]% #1 = label name
{\refstepcounter{equation}%
 \protected@write\@auxout{}{\string\newlabel{#1}{{\theequation}{\thepage}}}}
\makeatother

\begin{document}
We have
\begin{equation}
a=b \quad \text{and} \quad c=d
\tag*{\steplabel{eqab}(\theequation) and \steplabel{eqcd}(\theequation)}
\end{equation}
and equations \eqref{eqab} and \eqref{eqcd} are nice.
\end{document}