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使几个下支撑更加紧凑（看起来更美观）

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使几个下支撑更加紧凑（看起来更美观）

有没有办法使下支撑符号变细并减少其（垂直）距离以实现这一点：

在此处输入图片描述

我试过一种 tikz 版的较薄牙套。放大后可以看到，那只是权宜之计，看起来不太好看。

\documentclass[15pt, a4paper]{scrartcl}
\usepackage{amsmath,amssymb,stmaryrd}       

\usepackage{tikz}
\usetikzlibrary{decorations.pathreplacing}
\makeatletter
\def\Underbrace#1{%
  \@ifnextchar_{\tikz@@underbrace{#1}}{\tikz@@underbrace{#1}_{}}}
\def\tikz@@underbrace#1_#2{%
  \tikz[baseline=(a.base)] {\node[inner sep=2] (a) {\(#1\)};
  \draw[line cap=round,decorate,decoration={brace,amplitude=4pt}]
    (a.south east) -- node[pos=0.5,below,inner sep=7pt] {\(\scriptstyle #2\)} (a.south west);}}

\begin{document}

\[ p(x) \cdot x - \underbrace{r \cdot \Underbrace{\eta}_{\equiv 1} \cdot x}_{\text{variable costs}} \]

\end{document}

目前的结果是：

在此处输入图片描述

谢谢

答案1

您可以使用包MnSymbol，这样可以使用较小的括号。此外，您还可以使用，\smash这样较小的括号更靠近 eta 符号。最后，您可以使用包mathtools和，\clap以避免减号后有太多空格。

这里有展示我描述的 3 个连续改进的代码/图片：

\documentclass[15pt, a4paper]{scrartcl}
\usepackage{amsmath,mathtools}       
\usepackage{MnSymbol}
\begin{document}
\begin{align*} 
p(x)\cdot x-\underbrace{r\cdot\underbrace{\eta}_{\equiv1}
\cdot x}_{\text{variable costs}}\\[5pt]
%
p(x)\cdot x-\underbrace{r\cdot\underbrace{\smash{\eta}}_{\equiv1}
\cdot x}_{\text{variable costs}}\\[5pt]
%
p(x)\cdot x-\underbrace{r\cdot\underbrace{\smash{\eta}}_{\equiv1}
\cdot x}_{\clap{\scriptsize variable costs}}
\end{align*}
\end{document}

在此处输入图片描述

您甚至可以使用第二次猛击来抬起更大的支架：

p(x)\cdot x-\underbrace{\smash{r\cdot\underbrace{\smash{\eta}}_{\equiv1}
\cdot x}\vspace{6mm}}_{\clap{\scriptsize variable costs}}

您可以在其中使用“6mm”值。

在此处输入图片描述

答案2

基于其他答案，我导入了来自的内容来MnSymbol定义\underbrace和\overbrace。

然后我将它们一起使用\mathclap。

在此处输入图片描述

代码：

\documentclass{scrartcl}
\usepackage{mathtools}


%------------------ MnSymbol stuff ------------------%

\DeclareFontFamily{OMX}{MnSymbolE}{}
\DeclareSymbolFont{largesymbolsX}{OMX}{MnSymbolE}{m}{n}
\DeclareFontShape{OMX}{MnSymbolE}{m}{n}{
    <-6>  MnSymbolE5
   <6-7>  MnSymbolE6
   <7-8>  MnSymbolE7
   <8-9>  MnSymbolE8
   <9-10> MnSymbolE9
  <10-12> MnSymbolE10
  <12->   MnSymbolE12}{}

\DeclareMathSymbol{\downbrace}    {\mathord}{largesymbolsX}{'251}
\DeclareMathSymbol{\downbraceg}   {\mathord}{largesymbolsX}{'252}
\DeclareMathSymbol{\downbracegg}  {\mathord}{largesymbolsX}{'253}
\DeclareMathSymbol{\downbraceggg} {\mathord}{largesymbolsX}{'254}
\DeclareMathSymbol{\downbracegggg}{\mathord}{largesymbolsX}{'255}
\DeclareMathSymbol{\upbrace}      {\mathord}{largesymbolsX}{'256}
\DeclareMathSymbol{\upbraceg}     {\mathord}{largesymbolsX}{'257}
\DeclareMathSymbol{\upbracegg}    {\mathord}{largesymbolsX}{'260}
\DeclareMathSymbol{\upbraceggg}   {\mathord}{largesymbolsX}{'261}
\DeclareMathSymbol{\upbracegggg}  {\mathord}{largesymbolsX}{'262}
\DeclareMathSymbol{\braceld}      {\mathord}{largesymbolsX}{'263}
\DeclareMathSymbol{\bracelu}      {\mathord}{largesymbolsX}{'264}
\DeclareMathSymbol{\bracerd}      {\mathord}{largesymbolsX}{'265}
\DeclareMathSymbol{\braceru}      {\mathord}{largesymbolsX}{'266}
\DeclareMathSymbol{\bracemd}      {\mathord}{largesymbolsX}{'267}
\DeclareMathSymbol{\bracemu}      {\mathord}{largesymbolsX}{'270}
\DeclareMathSymbol{\bracemid}     {\mathord}{largesymbolsX}{'271}

\makeatletter
\def\horiz@expandable#1#2#3#4#5#6#7#8{%
  \@mathmeasure\z@#7{#8}%
  \@tempdima=\wd\z@
  \@mathmeasure\z@#7{#1}%
  \ifdim\noexpand\wd\z@>\@tempdima
    $\m@th#7#1$%
  \else
    \@mathmeasure\z@#7{#2}%
    \ifdim\noexpand\wd\z@>\@tempdima
      $\m@th#7#2$%
    \else
      \@mathmeasure\z@#7{#3}%
      \ifdim\noexpand\wd\z@>\@tempdima
        $\m@th#7#3$%
      \else
        \@mathmeasure\z@#7{#4}%
        \ifdim\noexpand\wd\z@>\@tempdima
          $\m@th#7#4$%
        \else
          \@mathmeasure\z@#7{#5}%
          \ifdim\noexpand\wd\z@>\@tempdima
            $\m@th#7#5$%
          \else
           #6#7%
          \fi
        \fi
      \fi
    \fi
  \fi}

\def\overbrace@expandable#1#2#3{\vbox{\m@th\ialign{##\crcr
  #1#2{#3}\crcr\noalign{\kern2\p@\nointerlineskip}%
  $\m@th\hfil#2#3\hfil$\crcr}}}
\def\underbrace@expandable#1#2#3{\vtop{\m@th\ialign{##\crcr
  $\m@th\hfil#2#3\hfil$\crcr
  \noalign{\kern2\p@\nointerlineskip}%
  #1#2{#3}\crcr}}}

\def\overbrace@#1#2#3{\vbox{\m@th\ialign{##\crcr
  #1#2\crcr\noalign{\kern2\p@\nointerlineskip}%
  $\m@th\hfil#2#3\hfil$\crcr}}}
\def\underbrace@#1#2#3{\vtop{\m@th\ialign{##\crcr
  $\m@th\hfil#2#3\hfil$\crcr
  \noalign{\kern2\p@\nointerlineskip}%
  #1#2\crcr}}}

\def\bracefill@#1#2#3#4#5{$\m@th#5#1\leaders\hbox{$#4$}\hfill#2\leaders\hbox{$#4$}\hfill#3$}

\def\downbracefill@{\bracefill@\braceld\bracemd\bracerd\bracemid}
\def\upbracefill@{\bracefill@\bracelu\bracemu\braceru\bracemid}

\def\upbrace@expandable{%
  \horiz@expandable
    \upbrace
    \upbraceg
    \upbracegg
    \upbraceggg
    \upbracegggg
    \upbracefill@}
\def\downbrace@expandable{%
  \horiz@expandable
    \downbrace
    \downbraceg
    \downbracegg
    \downbraceggg
    \downbracegggg
    \downbracefill@}

\DeclareRobustCommand{\overbrace}[1]{\mathop{\mathpalette{\overbrace@expandable\downbrace@expandable}{#1}}\limits}
\DeclareRobustCommand{\underbrace}[1]{\mathop{\mathpalette{\underbrace@expandable\upbrace@expandable}{#1}}\limits}
\makeatother

%------------------ MnSymbol stuff ------------------%


\begin{document}

\[ p(x) \cdot x - \overbrace{r \cdot \underbrace{\smash{\eta}}_{\equiv 1} \cdot x}^{\mathclap{\text{\tiny variable costs}}} \]

\end{document}

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