在字母下绘制弧线

Question

我一直在尝试画一些类似的东西

有人能帮我写代码吗？我不知道该怎么做。非常感谢您的帮助。

编辑：根据评论，我得到了代码

\documentclass{article}
\usepackage[usenames,dvipsnames]{pstricks} 
\usepackage{pstricks-add}
\usepackage{epsfig}
\usepackage{pst-grad} % For gradients
\usepackage{pst-plot} % For axes
\usepackage[space]{grffile} % For spaces in paths
\usepackage{etoolbox} % For spaces in paths
\makeatletter % For spaces in paths
\patchcmd\Gread@eps{\@inputcheck#1 }{\@inputcheck"#1"\relax}{}{}
\makeatother 
\documentclass{article}
\usepackage{tikz-cd}
\usepackage{amsmath}
\usetikzlibrary{arrows}

\def\ac{\rotatebox[origin=c]{90}{$\dashv$}} %rotate dash anti-cw
\def\cw{\rotatebox[origin=c]{-90}{$\dashv$}} %rotate dash cw
%\tikzset{adj/.style={pos=0.545,outer sep=3pt}} %adjust label position along path

\begin{document}
\begin{tikzcd}[column sep=small]
    q 
& &
    \arrow[bend left,above]{ll}{a} -q 
    %\arrow[bend left,above, adj]{ll}{U_G} Cat \arrow[bend left,below]{rr}{F_P}
& &
  q 
& &
    q^2 
    & & 
    -q^2\arrow[bend left,above]{ll}{b}
    & &
    q^2
    & &
    -q^2\arrow[bend left,above]{ll}{b}
    & & 
    -q
\end{tikzcd}
\end{document}

这使

但我无法画出大下划线。

Answer 1

只需以与添加箭头类似的方式添加另一个箭头即可。

\documentclass{article}
\usepackage{tikz-cd}
\usepackage{amsmath}
\usetikzlibrary{arrows}

\def\ac{\rotatebox[origin=c]{90}{$\dashv$}} %rotate dash anti-cw
\def\cw{\rotatebox[origin=c]{-90}{$\dashv$}} %rotate dash cw
%\tikzset{adj/.style={pos=0.545,outer sep=3pt}} %adjust label position along path

\begin{document}
\begin{tikzcd}[column sep=small]
    q 
& &
    \arrow[bend left,above]{ll}{a} -q 
    %\arrow[bend left,above, adj]{ll}{U_G} Cat \arrow[bend left,below]{rr}{F_P}
& &
   q  
& &
    q^2 
    & & 
    -q^2\arrow[bend left,above]{ll}{b}
    & &
    q^2
    & &
    -q^2\arrow[bend left,above]{ll}{b}
    & & 
    \arrow[bend left,above]{llllllllll}{b} % <--- addition
    -q\\
    &&  &&&&&\\
\end{tikzcd}
\end{document}