TikZ 中方程下的箭头

Question

我一直在使用 Ti钾Z 绘制此类方程

使用这个

\begin{equation}
\begin{tikzpicture}[
  inner sep=0pt,
  outer sep=0pt,
  baseline=(hat.base),
]
  \path[every node/.append style={anchor=base west}]
    (0,0)
    \foreach \name/\code in {
      bra0/,
      bra/Z,
      sub/_1,
      sub2/_2,
      angle/%
      } {
      node (\name) {$\code$}
      (\name.base east)
    }
  ;
  \path[
    every node/.append style={
      anchor=base,
      font=\slshape\scriptsize,
    },
  ]
    (bra0.base) -- node[below=3\baselineskip] (geb_2) {12} (ket)
  ;
  \begin{scope}[
    >={Stealth[length=5pt]},
    thick,
    rounded corners=0pt,
    shorten <=.3em,
    shorten >=.3em,
  ]

    \def\GebArrow#1#2#3{
      \draw[<->]
        (#2.north) ++(0, .3em) coordinate (tmp)
        (#1) |- (tmp) -| (#3)
      ;%
    }
    \GebArrow{sub2}{geb_2}{sub}
  \end{scope}
\end{tikzpicture}
\end{equation}

但我似乎找不到这个方程的解法

这看起来更容易，但我不知道如何制作不连接的简单箭头。

Answer 1

我不确定我是否理解了您的代码的作用。但是，使用该tikzmark库重现您的手写公式确实非常简单。当此库包含时，它会更加简单\tikzmarknode，并且当更新正式发布在 CTAN 上时，我很乐意更新我的代码。在此之前，您可以使用

\documentclass{article}
\usepackage{amsmath,amssymb,braket,tikz}
\usetikzlibrary{tikzmark,calc}
\begin{document}
\begin{equation}
 \phi_{\tikzmark{1-1}1\tikzmark{1-2}}
 ~=~x_{\tikzmark{2-1}1\tikzmark{2-2}1\tikzmark{2-3}}\,
 \psi_{\tikzmark{3-1}1\tikzmark{3-2}}+
 x_{\tikzmark{4-1}1\tikzmark{4-2}2\tikzmark{4-3}}\,
 \psi_{\tikzmark{5-1}2\tikzmark{5-2}}\;.
\end{equation}
\begin{tikzpicture}[overlay,remember picture]
\foreach \X in {1,2,4}
{ \draw[latex-,shorten <=1pt] ($(pic cs:\X-1)!0.5!(pic cs:\X-2)$) 
 -- ++ (0,-1) node[below]{$\scriptstyle1$};}
\foreach \X [evaluate=\X as \Y using {int(\X+1)},count=\Z]in {2,4}
{\draw[latex-latex,shorten <=1pt,shorten >=1pt] 
 ($(pic cs:\X-2)!0.5!(pic cs:\X-3)$) 
 -- ++ (0,-.5) -| ($(pic cs:\Y-1)!0.5!(pic cs:\Y-2)$) 
 node[below,pos=0.25]{$\scriptstyle\Z\Z$};}
\end{tikzpicture}
\end{document}

以下是即将推出的版本tikzmark。（我很抱歉没有阅读手册，这个新版本让事情真的非常简单。哇！）

\documentclass{article}
\usepackage{amsmath,tikz}
\usetikzlibrary{tikzmark}
\begin{document}
\begin{equation}
 \phi_{\tikzmarknode{11}{1}}
 ~=~x_{\tikzmarknode{21}{1}\tikzmarknode{22}{1}}\,
 \psi_{\tikzmarknode{31}{1}}+
 x_{\tikzmarknode{41}{1}\tikzmarknode{42}{2}}\,
 \psi_{\tikzmarknode{51}{2}}\;.
\begin{tikzpicture}[remember picture,overlay]
\foreach \X in {1,2,4}
{ \draw[latex-,shorten <=1pt] (\X1) 
 -- ++ (0,-1) node[below] (l\X) {$\scriptstyle1$};}
\foreach \X [evaluate=\X as \Y using {int(\X+1)},count=\Z]in {2,4}
{\draw[latex-latex,shorten <=1pt,shorten >=1pt] 
 (\X2)  -- ++ (0,-.5) -| (\Y1)
 node[below,pos=0.25]{$\scriptstyle\Z\Z$};}
\end{tikzpicture}
\end{equation}
\end{document}

Answer 2

另一个简短的代码是pstricks：

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

\begin{document}

    \[ \begin{postscript}
    \everypsbox{\scriptstyle}
    %% Some nodes
    \phi_{\rnode[b]{F}{1}} = x_{\rnode[b]{a}{1}\rnode[b]{b}{1}}\varphi_{\rnode[b]{c}{1}} + x_{\rnode[b]{d}{1} \rnode[b]{e}{2}}\varphi_{\rnode[b]{g}{2}}
    %% Remaining nodes and connections
    \psset{angle=-90, linewidth=0.6pt, linejoin=1, arm=4.5mm, arrows=<->, arrowinset=0.1, nodesep=2pt, labelsep=1.5pt}
    \foreach \s/\t in {F/G, a/A, d/D}{\uput{1cm}[d](\s){\rnode[t]{\t}{1}}\ncline[arrows=->]{\t}{\s}}
    \ncbar{b}{c}\nbput{11}
    \ncbar{e}{g}\nbput{22}
    \end{postscript} \]%

\end{document}