如何减少具有特定论文格式的 empheq 包中方程标签和方程之间的空间？

Question

以下是我的示例：

\documentclass[%
    11pt,
    %pagesize=pdftex,
    %paper=letter,
    pagesize,
    headsepline,
    parskip=half,
    english,
    twoside,
    headings=chapterprefix,
    %pointlessnumbers % Chapters always without point
    numbers=noenddot
    %DIV=14
]{scrbook}


\usepackage{mathtools}

\newcommand{\Sf}{\mathbf{S}_f}
\newcommand{\gradphi}[1]{(\nabla\phi)_{#1}}
\newcommand{\U}{\mathbf{U}}


\usepackage{empheq}
\usepackage[most]{tcolorbox}
\newtcbox{\mymath}[1][]{%
    nobeforeafter, 
    math upper, 
    tcbox raise base, 
    enhanced, 
    colframe=black!30!black, 
    colback=black!10, 
    boxrule=1pt, #1}

\usepackage{geometry}
\geometry{
    % Royal
    top=2.0cm,%
    bottom=2.5cm,%
    left=2.2cm,%
    right=1.7cm,%
    paperwidth=15.59cm,%
    paperheight=23.39cm%
}

\begin{document}
\begin{empheq}[box={\mymath[drop lifted shadow, sharp corners]}]{align}
    \label{eq:phieulerimpl}
    \left(\frac{\partial \phi}{\partial t}\right)_c^{n+1} & = 
        \dfrac{1}{\Omega_c} \left[ \sum_f D_f \gradphi{f}^{n+1} \cdot \Sf - \sum_f \U_f \phi_f^{n+1} \cdot \Sf \right] + \nonumber \\
        & + S(\phi_c^{n+1}) + O(\delta t) + O(h^2),
\end{empheq}
\end{document}

输出结果如下：

我知道我可以改变给包的选项geometry，但是页面的格式是固定的。

我该怎么做才能减少标签和公式之间的空白？我同意标签放在下一行，但垂直空间应该减少。

Answer 1

除了写出方程式和一个内部分隔较少的盒子外，没有太多其他内容

\documentclass[%
    11pt,
    %pagesize=pdftex,
    %paper=letter,
    pagesize,
    headsepline,
    parskip=half,
    english,
    twoside,
    headings=chapterprefix,
    %pointlessnumbers % Chapters always without point
    numbers=noenddot
    %DIV=14
]{scrbook}

\usepackage{mathtools}

\newcommand{\Sf}{\mathbf{S}_f}
\newcommand{\gradphi}[1]{(\nabla\phi)_{#1}}
\newcommand{\U}{\mathbf{U}}


\usepackage{empheq}
\usepackage[most]{tcolorbox}
\newtcbox{\mymath}[1][]{%
    nobeforeafter, 
    math upper, 
    tcbox raise base, 
    enhanced, 
    colframe=black!30!black, 
    colback=black!10, 
    boxrule=1pt,
    #1}

\usepackage{geometry}
\geometry{
    % Royal
    top=2.0cm,%
    bottom=2.5cm,%
    left=2.2cm,%
    right=1.7cm,%
    paperwidth=15.59cm,%
    paperheight=23.39cm%
}

\begin{document}
\begin{empheq}[box={\mymath[drop lifted shadow, sharp corners]}]{equation}
  \label{eq:phieulerimpl}
  \begin{aligned}
    \MoveEqLeft \left(\frac{\partial \phi}{\partial t}\right)_c^{n+1}
    =
    \dfrac{1}{\Omega_c} \Bigl[\, \sum_f D_f \gradphi{f}^{n+1} \cdot
    \Sf
    \\
    & - \sum_f \U_f \phi_f^{n+1} \cdot \Sf \Bigr]      + S(\phi_c^{n+1}) + O(\delta t) + O(h^2),
  \end{aligned}
\end{empheq}
\end{document}

Answer 2

不错的 @daleif 答案的一个小变化（+1）：使用来自包中的和环境的\medmath宏：nccmathmultlinedmathtools

\documentclass[%
    11pt,
    %pagesize=pdftex,
    %paper=letter,
    pagesize,
    headsepline,
    parskip=half,
    english,
    twoside,
    headings=chapterprefix,
    %pointlessnumbers % Chapters always without point
    numbers=noenddot
    %DIV=14
]{scrbook}


\usepackage{nccmath, mathtools}     % <---

\newcommand{\Sf}{\mathbf{S}_f}
\newcommand{\gradphi}[1]{(\nabla\phi)_{#1}}
\newcommand{\U}{\mathbf{U}}

\usepackage{empheq}
\usepackage[most]{tcolorbox}
\newtcbox{\mymath}[1][]{%
    nobeforeafter,
    math upper,
    tcbox raise base,
    enhanced,
    colframe=black!30!black,
    colback=black!10,
    boxrule=1pt, #1}

\usepackage{geometry}
\geometry{
    % Royal
    top=2.0cm,%
    bottom=2.5cm,%
    left=2.2cm,%
    right=1.7cm,%
    paperwidth=15.59cm,%
    paperheight=23.39cm%
}

\begin{document}
\begin{empheq}[box={\mymath[drop lifted shadow, sharp corners]}]{equation}
    \label{eq:phieulerimpl}
    \medmath{\begin{multlined} % <--- MEDMATH, MULTLINED
\biggl(\frac{\partial \phi}{\partial t}\biggr)_c^{n+1} 
    = \dfrac{1}{\Omega_c} \biggl[ \sum_f D_f \gradphi{f}^{n+1} \Sf - \sum_f \U_f \phi_f^{n+1} \Sf \biggr]+ \\
    + S(\phi_c^{n+1}) + O(\delta t) + O(h^2),
    \end{multlined}}
\end{empheq}
\end{document}