1

I have the following problem. I have a system of two equations. I used the package subnumcases. Unfortunately the equations are too long and the equation number overlap the equation itself. I tried Resizebox, to reduce the font, but they always crash. Texmaker tells that a bracket is missing. I am wondering way. I attach the code and the output. Could you help me please?enter image description here

\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}
2

Three solutions:

  • use the \medmath command from nccmath: it reduces the size to about 80 % of \displaystyle,
  • replace subnumcases by an align environment inside subequations. The brace can be obtained as an option of the empheq environment, and the long line will be split with either aligned or multlined (from mathtools, which is loaded by empheq):

Code:

\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} 

Also, I took the liberty to replace in your code, \bar with \widebar (borrowed from mathabx), which fits better capital letters, and the subscripts as \mathrm.

enter image description here

Edit:

As observed by @Zarko, you also can remove the multiplication \cdots and use the flalign environment: this code

    \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}

results in

enter image description here

  • Also dots for multiplication can be omitted ... :-) – Zarko May 18 '16 at 19:20
  • @Zarko: Right, if we use flalign. I've added your suggestion (with credits). Thanks! – Bernard May 18 '16 at 19:39
0
\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}

enter image description here

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