在子方程环境中改进外观的几次尝试

Question

我正在尽一切努力寻找所有可能性，以便将第一个方程式最好地置于环境中的中心subequations。我无法使用该选项，alignat因为彩色枚举（这里有@Werner 的完整代码列举书中方程式的一个优雅方面）

\documentclass{book}

\usepackage{mathtools}
\usepackage[svgnames, dvipsnames, table, x11names]{xcolor}
\usepackage{pifont}

\definecolor{ocre}{RGB}{243,102,25} 
%----------------------------------------------------------------------------------
%   Change number equations with sections
%----------------------------------------------------------------------------------
\usepackage{chngcntr}
\counterwithin{equation}{section}

\renewcommand{\theequation}{\thesection-\arabic{equation}}
\newcommand{\eqnnumsymbol}{\textcolor{ocre}{\reflectbox{\ding{228}}}}

\makeatletter
\newtagform{bbrackets}% <name>
  [\textbf]% Internal style
  {(}% Left bracket
  {\ifnum\pdfstrcmp{\@currenvir}{equation}=0
     \eqnnumsymbol%
   \else
     \ifnum\pdfstrcmp{\@currenvir}{align}=0
       \eqnnumsymbol%
     \fi
   \fi
   )}% Right bracket
\makeatother
\usetagform{bbrackets}

\begin{document}

See both~\eqref{eq:eqn1} and~\eqref{eq:eqn2}. Also see~\eqref{eq:eqn3}.

\begin{equation}
  \oint \mathbf{E} \cdot d \mathbf{a} = \int \rho \, \mathrm{d}v \label{eq:eqn1}
\end{equation}

\begin{equation}
  \oint \mathbf{B} \cdot d \mathbf{a} =  \mathbf{0} \label{eq:eqn2}
\end{equation}

\begin{align}
  abc \label{eq:eqn3}
\end{align}

\end{document}

消失在我的书中。

我尝试反转符号&或添加它，但无济于事。你有什么建议吗？谢谢大家。

我正在添加 MWE 和屏幕截图。

\documentclass[a4paper,12pt]{article}
\usepackage{amsmath,amssymb}
\begin{document}
\begin{subequations}
\begin{align}
\overline {F} &=-\overline{\nabla}U(\bar{r})+ \overline{\nabla} \times \overline{W}(\bar{r}) \label{Undec}\\
U(\bar{r})&=\frac1{4\pi}\int_{\mathcal{V}}\frac{D(\bar{r}')}{R}dV', \quad \overline{W}(\bar{r})=\frac1{4\pi}\int_{\mathcal{V}}\frac{\overline{C}(\bar{r}')}{R}dV' \label{Undec1}
\end{align}
\end{subequations}
\end{document}

附录

通过gather选择我得到了这个：

Answer 1

如果您不需要等式在等号处对齐，那么我相信gather环境会满足您的要求：

\documentclass{article}
\usepackage{amsmath}

% From egreg: <https://tex.stackexchange.com/a/501075/73317>
\newcommand{\diff}{\mathop{}\!\mathrm{d}}

\begin{document}

\begin{subequations}
\begin{gather}
\overline{F} = - \overline{\nabla}U(\bar{r}) +
               \overline{\nabla} \times \overline{W}(\bar{r}) \label{Undec}\\
U(\bar{r}) = \frac{1}{4\pi} \int_{\mathcal{V}} \frac{D(\bar{r}')}{R} \diff V',
\quad
\overline{W}(\bar{r}) =
  \frac{1}{4\pi} \int_{\mathcal{V}} \frac{\overline{C}(\bar{r}')}{R} \diff V'
  \label{Undec1}
\end{gather}
\end{subequations}

\end{document}

请注意，我删除了&等号前的 （ 中没有对齐制表符gather）。我还使用了\diff命令来自 egreg为差分。

这与方程标签中的红色箭头相同。首先使用相同的技术检查环境名称（存在大量冗余，我们将在下面将其删除）：

\documentclass{article}
\usepackage{mathtools}
\usepackage{graphicx}
\usepackage{xcolor}
\usepackage{pifont}

% From egreg: <https://tex.stackexchange.com/a/501075/73317>
\newcommand{\diff}{\mathop{}\!\mathrm{d}}

\definecolor{ocre}{RGB}{243,102,25}
\counterwithin{equation}{section}

\renewcommand{\theequation}{\thesection-\arabic{equation}}
\newcommand{\eqnnumsymbol}{\textcolor{ocre}{\reflectbox{\ding{228}}}}

\makeatletter

\newtagform{bbrackets}% <name>
  [\textbf]% Internal style
  {(}% Before
  {\ifnum\pdfstrcmp{\@currenvir}{equation}=0
     \eqnnumsymbol
   \else
     \ifnum\pdfstrcmp{\@currenvir}{align}=0
       \eqnnumsymbol
     \else
       \ifnum\pdfstrcmp{\@currenvir}{gather}=0
         \eqnnumsymbol
       \fi
     \fi
   \fi
   )}% After

\makeatother

\usetagform{bbrackets}

\begin{document}

\section{First section}

\begin{subequations}
\begin{gather}
\overline{F} = - \overline{\nabla}U(\bar{r}) +
               \overline{\nabla} \times \overline{W}(\bar{r}) \label{Undec}\\
U(\bar{r}) = \frac{1}{4\pi} \int_{\mathcal{V}} \frac{D(\bar{r}')}{R} \diff V',
\quad
\overline{W}(\bar{r}) =
  \frac{1}{4\pi} \int_{\mathcal{V}} \frac{\overline{C}(\bar{r}')}{R} \diff V'
  \label{Undec1}
\end{gather}
\end{subequations}

\end{document}

现在，以更优雅的方式在内部进行环境名称检查\newtagform{bbrackets}[...]{...}{...}，这样您只需将希望方程标签具有红色箭头的环境添加到逗号列表中（参见\forcsvlist{...}{equation, align, gather}下面的行）。

\documentclass{article}
\usepackage{mathtools}
\usepackage{graphicx}
\usepackage{xcolor}
\usepackage{pifont}
\usepackage{etoolbox}

% From egreg: <https://tex.stackexchange.com/a/501075/73317>
\newcommand{\diff}{\mathop{}\!\mathrm{d}}

\definecolor{ocre}{RGB}{243,102,25}

\counterwithin{equation}{section}
\renewcommand{\theequation}{\thesection-\arabic{equation}}
\newcommand{\eqnnumsymbol}{\textcolor{ocre}{\reflectbox{\ding{228}}}}

\makeatletter

% Helper macro used to insert the arrow symbol from pifont if the current
% environment (\@currenvir) is in the list passed to \forcsvlist.
\newcommand*{\@usearrowifsame}[2]{%
  \ifstrequal{#1}{#2}{\eqnnumsymbol\listbreak}{}%
}

\newtagform{bbrackets}% <name>
  [\textbf]% Internal style
  {(}% Before
  {% Insert the red arrow from pifont in the equation tag when we are inside
   % one of the environments listed in the second argument.
   \forcsvlist{\expandafter\@usearrowifsame\expandafter{\@currenvir}}%
              {equation, align, gather}%
   )}% After

\makeatother

\usetagform{bbrackets}

\begin{document}

\section{First section}

\begin{subequations}
\begin{gather}
\overline{F} = - \overline{\nabla}U(\bar{r}) +
               \overline{\nabla} \times \overline{W}(\bar{r}) \label{Undec}\\
U(\bar{r}) = \frac{1}{4\pi} \int_{\mathcal{V}} \frac{D(\bar{r}')}{R} \diff V',
\quad
\overline{W}(\bar{r}) =
  \frac{1}{4\pi} \int_{\mathcal{V}} \frac{\overline{C}(\bar{r}')}{R} \diff V'
  \label{Undec1}
\end{gather}
\end{subequations}

\end{document}