为什么“\x-1”在节点名中不起作用？

Question

如何修复使用引用节点时出现的错误\x-1？

它在 中可以工作[below left = \x-1]，但在 中不工作\draw[->] (\x-1) to (\x)。

\documentclass[tikz]{standalone}
\usepackage{pgffor,pgfmath}
\usetikzlibrary{positioning, arrows.meta}

\begin{document}
\begin{tikzpicture}[node distance = 1.00cm and 0.10cm, 
    every node/.style = {draw, circle, fill = blue!20}]

  \node (1) {$1$};

  \foreach \x in {2, ..., 7} {
    \node (\x) [below left = \x-1] {$\x$};
    \draw[->] (\x-1) to (\x);     % not work: no shape named 2-1 
  }
\end{tikzpicture}
\end{document}

我也尝试过

\foreach \x [remember = \x as \lastx] in {2, ..., 7} {
    \node (\x) [below left = \x-1] {$\x$};
    \draw[->] (\lastx) to (\x);   % not work: undefined control sequence. \lastx }
}

Answer 1

\x-1被评估为2-1等 Ti钾出于充分的理由，Z 并不（必然）期望此位置有一个数字。1.north您也可以写1.90，例如1.east 1.0等等。因此，如果 Ti钾Z 将节点名称解释为数字，否则就会变得模棱两可。

remember但是，如果我添加适当的初始值（对于第一步），我不会遇到任何问题。

\documentclass[tikz]{standalone}
\usepackage{pgffor,pgfmath}
\usetikzlibrary{positioning, arrows.meta}

\begin{document}
\begin{tikzpicture}[node distance = 1.00cm and 0.10cm, 
    every node/.style = {draw, circle, fill = blue!20}]

  \node (1) {$1$};

  \foreach \x [remember=\x as \lastx (initially 1)] in {2, ..., 7} {
    \node (\x) [below left = \x-1] {$\x$};
    \draw[->] (\lastx) to (\x);     % not work: no shape named 2-1 
  }
\end{tikzpicture}
\end{document}

Answer 2

\x-1不在节点名称位置内进行评估，但您可以在构造的可选参数内强制进行一些评估\foreach。

\documentclass[tikz]{standalone}
\usepackage{pgffor,pgfmath}
\usetikzlibrary{positioning, arrows.meta}

\begin{document}
\begin{tikzpicture}[node distance = 1.00cm and 0.10cm, 
    every node/.style = {draw, circle, fill = blue!20}]

  \node (1) {$1$};

  \foreach \x [evaluate=\x as \nx using {int(\x-1)}] in {2, ..., 7} {
    \node (\x) [below left = of \nx] {$\x$};
    \draw[->] (\nx) to (\x);     % not work: no shape named 2-1 
  }
\end{tikzpicture}
\end{document}

注意：我还添加了of定位构造（您正在加载positioning库），结果有点不同。

Answer 3

您可以使用 强制完成整数求值\numexpr。

\documentclass[tikz]{standalone}
\usepackage{pgffor,pgfmath}
\usetikzlibrary{positioning, arrows.meta}

\begin{document}
\begin{tikzpicture}[node distance = 1.00cm and 0.10cm, 
    every node/.style = {draw, circle, fill = blue!20}]

  \node (1) {$1$};

  \foreach \x in {2, ..., 7} {
    \node (\x) [below left = \x-1] {$\x$};
    \draw[->] (\the\numexpr\x-1\relax) to (\x);
  }
\end{tikzpicture}
\end{document}