在 `\for` 循环内连接 tikz 节点会导致错误的连接点

Question

我想用 tikz 制作以下简单图表：

我实际上更喜欢使用 tikz\for循环将元素放在一起。但是，以下代码：

\begin{tikzpicture}[font=\small,>=latex, 
    add/.style={draw=black,circle,inner sep=0pt},
    branch/.style={fill=black,circle,minimum size=3pt,inner sep=0pt}%
  ] 
  \foreach \i in {2,4,6,8} {% 
    \node[add] at (-1,\i) (add\i) {$+$}; 
  } 
  \foreach \i[evaluate={\j=\i+1}] in {1,3,5,7} {% 
    \node[branch] at (-1,\i) (dot\i) {}; 
    \draw[->] (dot\i) -- (add\j); 
  }
\end{tikzpicture}

产生错误的图形。也就是说，箭头尖端连接到加法器的右侧：

而如果我只是\draw[->]在循环外手动编写部分代码，即使用以下代码：

\begin{tikzpicture}[font=\small,>=latex, 
    add/.style={draw=black,circle,inner sep=0pt},
    branch/.style={fill=black,circle,minimum size=3pt,inner sep=0pt}%
  ] 
  \foreach \i in {2,4,6,8} {% 
    \node[add] at (-1,\i) (add\i) {$+$}; 
  } 
  \foreach \i[evaluate={\j=\i+1}] in {1,3,5,7} {% 
    \node[branch] at (-1,\i) (dot\i) {}; 
  }
  \draw[->] (dot1) -- (add2);
  \draw[->] (dot3) -- (add4);
  \draw[->] (dot5) -- (add6);
  \draw[->] (dot7) -- (add8);
\end{tikzpicture}

我得到了正确的结果（我在问题开头给出的结果）。有什么想法可以解释为什么连接循环内的节点会弄乱连接点？

Answer 1

而不是\j in {2,4,6,8}你试图\j in {2.0,4.0,6.0,8.0}定位0锚点。

\documentclass{standalone}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}[font=\small,>=latex, 
    add/.style={draw=black,circle,inner sep=0pt},
    branch/.style={fill=black,circle,minimum size=3pt,inner sep=0pt}%
  ] 
  \foreach \i in {2,4,6,8} {% 
    \node[add] at (-1,\i) (add\i) {$+$}; 
  } 
  \foreach \i[evaluate={\j=int(\i+1)}] in {1,3,5,7} {% 
    \node[branch] at (-1,\i) (dot\i) {}; 
    \draw[->] (dot\i) -- (add\j); 
  }
\end{tikzpicture}
\end{document}

或者更简单

  \foreach \i/\j in {1/2,3/4,5/6,7/8} ...

Answer 2

\documentclass[ tikz,
                border =5mm]{standalone}

\begin{document}
\begin{tikzpicture}[font=\small,>=latex,
    add/.style={circle, draw=black, inner sep=0pt},
    branch/.style={circle, fill=black, minimum size=3pt, inner sep=0pt,
                   node contents={} }%
  ]
\foreach \i in {0,2,4,6} 
{%
\node (add\i) [add] at (-1,\i) {$+$};
\draw[->] (-1,\i-1) node[branch] -- (add\i);
}
\end{tikzpicture}
\end{document}

给出了期望的结果:-)