使用 subnumcase 时如何调整框大小

Question

我有以下问题。我有一个由两个方程组成的系统。我使用了 subnumcases 包。不幸的是，方程太长，方程编号与方程本身重叠。我尝试了 Resizebox 来减小字体，但它们总是崩溃。Texmaker 提示缺少一个括号。我想知道方法。我附上了代码和输出。你能帮我吗？

\documentclass[10pt,a4paper,titlepage]{book} 
\usepackage[paperwidth=165mm, paperheight=238mm, left=2.5cm,right=2cm,top=2cm,bottom=2cm]{geometry}

\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{showframe} 
\usepackage{cases}

\begin{document}

\begin{subnumcases}{} 
 C_{a} \frac{dT_{air}}{d\theta} = H_{1} \cdot (\bar{T}_{al}-T_{air}) + H_{2} \cdot   (T_{out} -T_{air}) +q_{out} \cdot (T_{out}-T_{air}) +\Sigma \Phi_{i,c} 
    \label{eq: coupled} 
   \\
 C_{al} \frac{d \bar{T}_{al}}{d \theta} = H_{3} \cdot (T_{air} -\bar{T}_{al})+H_{4} \cdot (T_{sol}-\bar{T}_{al})+ \Sigma \Phi_{i,r}  \label{eq:system} 
\end{subnumcases}

\end{document}

Answer 1

三种解决方案：

• 使用\medmath命令nccmath：它将尺寸缩小到大约 80% \displaystyle，
• subnumcases用align内部的环境替换subequations。括号可以作为empheq环境的一个选项获得，长行将被 或 分割aligned（multlined来自mathtools，由 加载empheq）：

代码：

\documentclass[10pt,a4paper,titlepage]{book}
\usepackage[paperwidth=165mm, paperheight=238mm, left=2.5cm,right=2cm,top=2cm,bottom=2cm]{geometry}

\usepackage{empheq, nccmath}
\usepackage{amsfonts}
\usepackage{showframe} \usepackage{cases}

\DeclareFontFamily{U}{mathx}{\hyphenchar\font45}
\DeclareFontShape{U}{mathx}{m}{n}{
<-6> mathx5 <6-7> mathx6 <7-8> mathx7
<8-9> mathx8 <9-10> mathx9
<10-12> mathx10 <12-> mathx12
}{}
\DeclareSymbolFont{mathx}{U}{mathx}{m}{n}
\DeclareFontSubstitution{U}{mathx}{m}{n}

\DeclareMathAccent{\widebar}{0}{mathx}{"73}

\begin{document}
%
\begin{subnumcases}
{}\medmath{C_\mathrm{a} \frac{dT_\mathrm{air}}{d\theta} = H_{1} \cdot (\bar{T}_\mathrm{al}-T_\mathrm{air}) + H_{2} \cdot (T_\mathrm{out} -T_\mathrm{air}) +q_\mathrm{out} \cdot (T_\mathrm{out}-T_\mathrm{air}) +\Sigma \Phi_{i,c}} \label{eq: coupled}\\
\medmath{C_\mathrm{al} \frac{d \widebar{T}_\mathrm{al}}{d \theta} = H_{3} \cdot (T_\mathrm{air} -\widebar{T}_\mathrm{al})+H_{4} \cdot (T_\mathrm{sol}-\widebar{T}_\mathrm{al})+ \Sigma \Phi_{i,r}} \label{eq:system}
\end{subnumcases}
\bigskip

\begin{subequations}
\begin{empheq}[left = \empheqlbrace]{align}{}C_{a} \frac{dT_\mathrm{air}}{d\theta} & = H_{1} \cdot (\bar{T}_\mathrm{al}-T_\mathrm{air}) + H_{2} \cdot (T_\mathrm{out} -T_\mathrm{air})%
\begin{aligned}[t] {}&+ q_\mathrm{out} \cdot (T_\mathrm{out}&-T_\mathrm{air}) \\[-0.8ex]
{} & +\Sigma \Phi_{i,c}\end{aligned} \label{eq:coupled}\\
\ C_\mathrm{al} \frac{d \widebar{T}_\mathrm{al}}{d \theta} & = H_{3} \cdot (T_\mathrm{air} -\widebar{T}_\mathrm{al})+H_{4} \cdot (T_\mathrm{sol}-\widebar{T}_\mathrm{al})+ \Sigma \Phi_{i,r} \label{eq-system}
\end{empheq}
\end{subequations}
\bigskip

\begin{subequations}
\begin{empheq}[left = \empheqlbrace]{align}%
C_{a} \frac{dT_\mathrm{air}}{d\theta} & = \!\begin{multlined}[t] %
H_{1} \cdot (\bar{T}_\mathrm{al}-T_\mathrm{air}) + H_{2} \cdot (T_\mathrm{out} -T_\mathrm{air})\\%
+ q_\mathrm{out} \cdot (T_\mathrm{out}-T_\mathrm{air}) +\Sigma \Phi_{i,c}%
\end{multlined} \label{eq:coupled}\\
\ C_\mathrm{al} \frac{d \widebar{T}_\mathrm{al}}{d \theta} & = H_{3} \cdot (T_\mathrm{air} -\widebar{T}_\mathrm{al})+H_{4} \cdot (T_\mathrm{sol}-\widebar{T}_\mathrm{al})+ \Sigma \Phi_{i,r} \label{eq-system}
\end{empheq}

\end{subequations}

\end{document} 

另外，我擅自在您的代码中用 （借用 ）替换了 \bar，\widebar它mathabx更适合大写字母，并将下标替换为\mathrm。

编辑：

正如@Zarko 所观察到的，您还可以删除乘法\cdot并使用flalign环境：此代码

    \begin{subequations}
    \begin{empheq}[left = \empheqlbrace]{flalign}%
   {}C_{a} \frac{dT_\mathrm{air}}{d\theta} & = H_{1} (\bar{T}_\mathrm{al}-T_\mathrm{air}) + H_{2}(T_\mathrm{out} -T_\mathrm{air})+ q_\mathrm{out} (T_\mathrm{out}-T_\mathrm{air}) +\Sigma \Phi_{i,c} \label{eq:coupled}\\%
    \ C_\mathrm{al} \frac{d \widebar{T}_\mathrm{al}}{d \theta} & = H_{3}(T_\mathrm{air} -\widebar{T}_\mathrm{al})+H_{4} (T_\mathrm{sol}-\widebar{T}_\mathrm{al})+ \Sigma \Phi_{i,r} \label{eq-system}
    \end{empheq}
    \end{subequations}

结果是

Answer 2

\documentclass[10pt,a4paper,titlepage]{book} 
\usepackage[paperwidth=165mm, paperheight=238mm, left=2.5cm,right=2cm,top=2cm,bottom=2cm]{geometry}

\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{showframe} 
\usepackage{cases}
\usepackage{graphicx}

\begin{document}

\noindent
\resizebox{\linewidth}{!}{\parbox{1.15\linewidth}{%
\begin{subnumcases}{} 
C_{a} \frac{dT_{air}}{d\theta} = H_{1} \cdot (\bar{T}_{al}-T_{air}) + H_{2} \cdot   (T_{out} -T_{air}) +q_{out} \cdot (T_{out}-T_{air}) +\Sigma \Phi_{i,c} 
        \label{eq: coupled} \\
C_{al} \frac{d \bar{T}_{al}}{d \theta} = H_{3} \cdot (T_{air} -\bar{T}_{al})+H_{4} \cdot (T_{sol}-\bar{T}_{al})+ \Sigma \Phi_{i,r}  \label{eq:system} 
\end{subnumcases}%
}}
\end{document}