方程下的连接箭头

Question

我正在尝试创建这个等式。箭头指向下标！我设法写出来了，但正如你所见，它并不完全正确。

Answer 1

您可以使用这个自制的tikzmark：

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

\newcommand\tikzmark[1]{\tikz[remember picture,overlay]\coordinate (#1);}

\begin{document}

\[
  Z_{\tikzmark{z1}1\tikzmark{z2}2} = X_{\tikzmark{x111}1\tikzmark{x112}1} Y_{\tikzmark{y121}1\tikzmark{y122}2}
  + X_{\tikzmark{x121}1\tikzmark{x122}2}Y_{\tikzmark{y221}2\tikzmark{y222}2}
\]

\begin{tikzpicture}[remember picture,overlay]
  \draw[latex-latex]
  ([shift={(2pt,-2pt)}]z1)
  -- ([shift={(2pt,-12pt)}]z1)
  -- node[midway, below] {$\scriptstyle 12$} ([shift={(2pt,-12pt)}]z2)
  -- ([shift={(2pt,-2pt)}]z2);

  \draw[latex-latex]
  ([shift={(2pt,-2pt)}]x111)
  -- ([shift={(2pt,-24pt)}]x111)
  -- node[midway, below] {$\scriptstyle 12$} ([shift={(2pt,-24pt)}]y122)
  -- ([shift={(2pt,-2pt)}]y122);

  \draw[latex-latex]
  ([shift={(2pt,-2pt)}]x112)
  -- ([shift={(2pt,-12pt)}]x112)
  -- node[midway, below] {$\scriptstyle 11$} ([shift={(2pt,-12pt)}]y121)
  -- ([shift={(2pt,-2pt)}]y121);

  \draw[latex-latex]
  ([shift={(2pt,-2pt)}]x121)
  -- ([shift={(2pt,-24pt)}]x121)
  -- node[midway, below] {$\scriptstyle 12$} ([shift={(2pt,-24pt)}]y222)
  -- ([shift={(2pt,-2pt)}]y222);

  \draw[latex-latex]
  ([shift={(2pt,-2pt)}]x122)
  -- ([shift={(2pt,-12pt)}]x122)
  -- node[midway, below] {$\scriptstyle 22$} ([shift={(2pt,-12pt)}]y221)
  -- ([shift={(2pt,-2pt)}]y221);
\end{tikzpicture}

\end{document}

我尝试了标准tikzmarktikz 库，但是没有用，所以我尝试了这个答案并且有效：

Answer 2

简短的代码如下pstricks：

\documentclass[11pt]{article}
\usepackage{amsmath}
\usepackage{pst-node, auto-pst-pdf}

\begin{document}

    \[ \begin{postscript}
\everypsbox{\scriptstyle}
%% Nodes
  Z_{\rnode[b]{Z1}{1}\rnode[b]{Z2}{2}} = X_{\rnode[b]{a}{1}\rnode[b]{b}{1}}Y_{\rnode[b]{c}{1} \rnode[b]{d}{2}} + X_{\rnode[b]{e}{1} \rnode[b]{f}{2}}X Y_{\rnode[b]{g}{2} \rnode[b]{h}{2}}
%% Connections
\psset{angle=-90, linejoin=1, arm=4.5mm, arrows=<->, arrowinset=0.1, nodesep=2pt, labelsep=1.5pt}
\ncbar[offsetA=-1pt, offsetB=-1.5pt]{Z1}{Z2}\nbput{12}
\ncbar[arm=9mm]{a}{d}\nbput{12}
\ncbar{b}{c}\nbput{11}
\ncbar{f}{g}\nbput{22}
\ncbar[arm=9mm]{e}{h}\nbput{12}
    \end{postscript} \]%

\end{document}