标记箭头的问题

Question

在序言中这样写道：

\usepackage{tikz}
\usetikzlibrary{chains,shapes.multipart}
\usetikzlibrary{scopes}
\usetikzlibrary{decorations.markings}
\usetikzlibrary{shapes,calc}
\usetikzlibrary{automata,positioning}

我有下图：

\begin{figure}
       \centering
       \begin{tikzpicture}[start chain=going right,>=latex,node distance=0pt]
         \node[draw,rectangle,on chain,minimum size=1.5cm] (rr) {$I$};
         \node[draw,rectangle,on chain,draw=white,minimum size=0.8cm]{};
         % the rectangular shape with vertical lines
        \node[rectangle split, rectangle split parts=5,
        draw, rectangle split horizontal,text height=1cm,text depth=0.5cm,on chain,inner ysep=0pt] (wa) {};
         \fill[white] ([xshift=-\pgflinewidth,yshift=-\pgflinewidth]wa.north west) rectangle ([xshift=-15pt,yshift=\pgflinewidth]wa.south);
        \node at (wa.east) (A){};
        \draw [-latex] (A) --+(30:1.5) coordinate (B1);
        \draw [-latex] (A) --+(-30:1.5) coordinate (B2);
         % the circle
         \node [draw,circle,on chain,minimum size=1cm] at (B1) (se1) {$U_1$};
         \draw [-latex] (se1) --+(0:1.3) coordinate (BB1);
         \node [draw,circle,on chain,minimum size=1cm] at (B2) (se2) {$U_2$};
         \draw [-latex] (se2) --+(0:1.3) coordinate (BB2);
         \node [draw,diamond,on chain,minimum size=0.2cm] at (BB1) (C3){};
         \draw [-latex] (C3)--+(0:1)node[midway,above] {$\mu$};
         % the arrows and labels
         \draw[<-] (wa.west) -- +(-20pt,0) node[midway,below] {$\lambda$};
         \draw[->] (C3.north) to[out=120, in=145] ([shift=(up:.3)] wa.west);
       \end{tikzpicture}
          \caption{The model represented as a queuing system.}
             \label{fig:queue}
       \end{figure}

如何在没有箭头的地方添加标签（下图显示了我想要添加标签的边缘）？

Answer 1

转换我的评论答案：

在曲线路径上，节点规范必须遵循to。因此，示例中的相关行应为：

\draw[->] (C3.north) to[out=120, in=145] node[below] {<label text>} ([shift=(up:.3)] wa.west);

还要注意，对于这个特定示例，您加载的许多库都不是必需的；只有chains和shapes（包括shapes.multipart）是必需的。

代码

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{chains,shapes}

\begin{document}
\begin{figure}
       \centering
       \begin{tikzpicture}[start chain=going right,>=latex,node distance=0pt]
         \node[draw,rectangle,on chain,minimum size=1.5cm] (rr) {$I$};
         \node[draw,rectangle,on chain,draw=white,minimum size=0.8cm]{};
         % the rectangular shape with vertical lines
        \node[rectangle split, rectangle split parts=5,
        draw, rectangle split horizontal,text height=1cm,text depth=0.5cm,on chain,inner ysep=0pt] (wa) {};
         \fill[white] ([xshift=-\pgflinewidth,yshift=-\pgflinewidth]wa.north west) rectangle ([xshift=-15pt,yshift=\pgflinewidth]wa.south);
        \node at (wa.east) (A){};
        \draw [-latex] (A) --+(30:1.5) coordinate (B1);
        \draw [-latex] (A) --+(-30:1.5) coordinate (B2);
         % the circle
         \node [draw,circle,on chain,minimum size=1cm] at (B1) (se1) {$U_1$};
         \draw [-latex] (se1) --+(0:1.3) coordinate (BB1);
         \node [draw,circle,on chain,minimum size=1cm] at (B2) (se2) {$U_2$};
         \draw [-latex] (se2) --+(0:1.3) coordinate (BB2);
         \node [draw,diamond,on chain,minimum size=0.2cm] at (BB1) (C3){};
         \draw [-latex] (C3)--+(0:1)node[midway,above] {$\mu$};
         % the arrows and labels
         \draw[<-] (wa.west) -- +(-20pt,0) node[midway,below] {$\lambda$};
         \draw[->] (C3.north) to[out=120, in=145] node[below] {$X$} ([shift=(up:.3)] wa.west); % <<< additions here
       \end{tikzpicture}
          \caption{The model represented as a queuing system.}
             \label{fig:queue}
       \end{figure}
\end{document}

输出