如何对 amsmath 对齐环境进行“本地”编号？

Question

我正在尝试在 amsmath align 环境中重新开始编号。我的 MWE 如下：

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}

\begin{document}

The following equations should be numbered $(1)$ and $(2)$.
\begin{align}
7x - 15y &= 2 \\
x + 2y &= 3 
\end{align}

The following should continue from the above numbering:
\begin{align}
4x - 5y &= 2 \\
6x + 7y &= 3 
\end{align}

But the following should be numbered $(1)$ and $(2)$ and not continued from the above.
\begin{align}
7x - 6y &= 4 \\
5x + 7y &= 3 
\end{align}

\end{document}

输出为：

我想要将编号为 (5) 和 (6) 的方程式编号为 (1) 和 (2)。

理想情况下，我希望编号方案“包含”在给定的一组相关方程中，这样一旦我重置编号计数器（比如说），它就不会影响全局编号方案。

请问我该如何实现这一点？

Answer 1

采用本地编号方案的通常方式是使用，尽管您可以根据需要subequation保存并重置主计数器，但这里显示了两种形式。equation

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\newcounter{saveeqn}
\begin{document}

The following equations should be numbered $(1)$ and $(2)$.
\begin{align}
7x - 15y &= 2 \\
x + 2y &= 3 
\end{align}

The following should continue from the above numbering:
\begin{align}
4x - 5y &= 2 \\
6x + 7y &= 3 
\end{align}

But the following should be numbered $(1)$ and $(2)$ and not continued from the above.
\begin{subequations}
\begin{align}
7x - 6y &= 4 \\
5x + 7y &= 3 
\end{align}
\end{subequations}

but you could do
\setcounter{saveeqn}{\value{equation}}\setcounter{equation}{0}
\begin{align}
7x - 6y &= 4 \\
5x + 7y &= 3 
\end{align}
\setcounter{equation}{\value{saveeqn}}

and then
\begin{align}
7x - 6y &= 4 \\
5x + 7y &= 3 
\end{align}

\end{document}

Answer 2

欢迎使用 TeX-SE！我个人不想这么做。但是，如果你真的想这么做，你可以使用\tag。

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}

\begin{document}

The following equations should be numbered $(1)$ and $(2)$.
\begin{align}
7x - 15y &= 2 \\
x + 2y &= 3 
\end{align}

The following should continue from the above numbering:
\begin{align}
4x - 5y &= 2 \\
6x + 7y &= 3 
\end{align}

But the following should be numbered $(1)$ and $(2)$ and not continued from the above.
\begin{align}
7x - 6y &= 4 \tag{1} \\
5x + 7y &= 3 \tag{2}
\end{align}

\end{document}