答案1
摘自该软件包的用户指南第 14 页mathtools
(重点添加了):
用户指南说下括号的默认宽度是 ca 5/18ex
= ca. 0.28ex
。以下屏幕截图显示了带有下括号的表达式,这些表达式涉及默认宽度以及默认宽度的一半、三分之二和四分之三;选择您最喜欢的。
\documentclass{article}
\usepackage{mathtools} % for '\underbracket' macro
\begin{document}
\[
% default width: 5/18ex = ca 0.28ex
\underbracket{1+2+3}_{\text{default}} % default width
+\underbracket[0.140ex]{1+2+3}_{\text{spaghetti}}% (1/2)default
+\underbracket[0.187ex]{1+2+3}_{\text{skinny}} % (2/3)default
+\underbracket[0.210ex]{1+2+3}_{\text{thin}} % (3/4)default
+\underbracket[0.280ex]{1+2+3}_{\text{default}} % default
\]
\end{document}
答案2
\underbracket
括号的粗细可以在和的第一个可选参数中指定\overbracket
。默认粗细是 的高度$\braceld$
(以当前数学字体为单位)。
\documentclass{article}
\usepackage{mathtools}
\begin{document}
\[
C(s) =
% use 0.5 thickness
\underbracket[.5pt]{\frac{K_1}{s}}_{\text{forced}} +
% use default thickness
\underbracket{\frac{K_2}{s+2}+\frac{K_3}{s+4}+\frac{K_4}{s+5}}_{\text{natural}}
\]
\end{document}
您还可以一次性更改括号的粗细:
\documentclass{article}
\usepackage{mathtools}
\usepackage{xpatch}
% change default thickness of brackets to .6pt
\MHInternalSyntaxOn
\xpatchcmd\upbracketfill
{\sbox\z@{$\braceld$}\edef\l_MT_bracketheight_fdim{\the\ht\z@}}
{\edef\l_MT_bracketheight_fdim{.6pt}}
{}{\fail}
\xpatchcmd\downbracketfill
{\sbox\z@{$\braceld$}\edef\l_MT_bracketheight_fdim{\the\ht\z@}}
{\edef\l_MT_bracketheight_fdim{.6pt}}
{}{\fail}
\MHInternalSyntaxOff
\begin{document}
\[
C(s) =
\underbracket{\frac{K_1}{s}}_{\text{forced}} +
\overbracket{\frac{K_2}{s+2}+\frac{K_3}{s+4}+\frac{K_4}{s+5}}^{\text{natural}}
\]
\end{document}