添加字母以对齐数字

Question

为了在公式编号中添加字母，我使用了以下代码

\newcounter{defcounter}
\setcounter{defcounter}{0}

\newenvironment{eee}[1]{%
\addtocounter{equation}{-1}
\refstepcounter{defcounter}
\renewcommand\theequation{E.#1.\thedefcounter}
\begin{equation}}
{\end{equation}}

现在我应该怎么做才能将此代码扩展到align环境？

Answer 1

您可以使用以下基础设施subequations：

\documentclass{article}
\usepackage{amsmath}

\newenvironment{eee}[2][equation]
 {\subequations\def\eeecurrent{#1}%
  \renewcommand\theequation{E.#2.\arabic{equation}}%
  \csname #1\endcsname}
 {\csname end\eeecurrent\endcsname
  \endsubequations\addtocounter{equation}{-1}}

\begin{document}

\begin{equation}
1=1
\end{equation}

\begin{eee}{one}
a=b
\end{eee}

\begin{eee}[align]{two}
a&=b\\
c&=d
\end{eee}

\begin{equation}
1=1
\end{equation}

\end{document}

在咨询了我的水晶球后，出现了一种变体：

\documentclass{article}
\usepackage{amsmath}
\usepackage{amsthm}

\theoremstyle{definition}
\newtheorem{exercise}{Exercise}
\newcounter{exnumber}[exercise]

\newenvironment{eee}[1][equation]
 {\addtocounter{equation}{-1}%
  \subequations\def\eeecurrent{#1}%
  \setcounter{equation}{\value{exnumber}}%
  \renewcommand\theequation{E.\theexercise.\arabic{equation}}%
  \csname #1\endcsname}
 {\csname end\eeecurrent\endcsname
  \setcounter{exnumber}{\value{equation}}%
  \endsubequations}

\begin{document}

\begin{equation}
1=1
\end{equation}

\begin{exercise}
Prove the following
\begin{eee}
a=b
\end{eee}
\end{exercise}

\begin{exercise}
Prove the following
\begin{eee}[align]
a&=b\\
c&=d
\end{eee}
and also the following
\begin{eee}[gather]
a=b\\
c=d
\end{eee}
\end{exercise}

\begin{equation}
1=1
\end{equation}

\end{document}