Tikz 中的图形（2 状态马尔可夫）

Question

我想在 Tikz 中制作下图：

我曾尝试使用代码这里，但很遗憾没有成功。

谁能给我提供一些制作这种图片的代码？

提前致谢。

Answer 1

一个相当简单的选择：

\documentclass[tikz,border=10pt,multi]{standalone}
\usetikzlibrary{positioning,arrows.meta,,bending}
\begin{document}
  \begin{tikzpicture}
    [
      >/.tip={Triangle[length=7.5pt,width=5pt,bend]},
      line width=1pt,
      my circle/.style={minimum width=10mm, circle, draw},
      my label/.style={above=10pt, anchor=mid}
    ]
    \node (1) [my circle] {$1$};
    \node (2) [my circle, right=75pt of 1] {$2$};
    \path [postaction={draw, {>[sep=5pt,reversed]}-{<[sep=5pt]}}, draw] (1) -- (2) node [very near start, my label] {$\alpha$}  node [very near end, my label] {$\beta$} ;
    \path [->, draw] (2.south east) arc (-135:135:5mm) node [near end, my label] {$1-\beta$};
    \path [->, draw] (1.south west) arc (-45:-315:5mm) node [near end, my label] {$1-\alpha$};
  \end{tikzpicture}
\end{document}

Answer 2

也许是这样的？

\documentclass[tikz,border=10pt]{standalone}
\usetikzlibrary{positioning}
\usetikzlibrary{decorations.markings}
\usetikzlibrary{decorations.text}

\begin{document}
\begin{tikzpicture}[
  node distance = 1cm and 2cm, >=latex,
  state/.style={draw, thick, circle, minimum size=8mm, inner sep=0pt},
  transitionA/.style args={#1}{very thick, ->, postaction={decorate},
    decoration={markings,
      mark=at position .8 with {\node[anchor=south,yshift=1pt] {#1};}}},
  transitionB/.style args={#1}{very thick, postaction={decorate},
    decoration={markings,
      mark=at position .26 with {\arrow{>}},
      mark=at position .2 with {\node[anchor=south,yshift=1pt] {#1};}}}
  ]

  \node[state] (1) {$1$};
  \node[state,right=of 1] (2) {$2$};

  \draw [transitionA={$1-\alpha$}] (1.south west) arc (-45:-315:4mm);
  \draw [transitionA={$1-\beta$}]  (2.south east) arc (-135:135:4mm);
  \draw [transitionB={$\alpha$}]   (1.east) -- (2.west);
  \draw [transitionB={$\beta$}]    (2.west) -- (1.east);
\end{tikzpicture}
\end{document}

版本 2（编辑：使用自动机库）

\documentclass[tikz,border=10pt]{standalone}
\usetikzlibrary{arrows,automata}

\begin{document}
\begin{tikzpicture}[node distance=2cm,->,>=latex,auto,
  every edge/.append style={thick}]
  \node[state] (1) {$1$};
  \node[state] (2) [right of=1] {$2$};  
  \path (1) edge[loop left]  node{$1-\alpha$} (1)
            edge[bend left]  node{$\alpha$}   (2)
        (2) edge[loop right] node{$1-\beta$}  (2)
            edge[bend left] node{$\beta$}     (1);
\end{tikzpicture}
\end{document}

Answer 3

请尝试以下操作：

    \documentclass[tikz]{standalone}
    \usetikzlibrary{automata,decorations.markings,positioning}

    \begin{document}
        \begin{tikzpicture}[
                >=latex,
      decoration = {markings,
                    mark=at position .3 with {\arrow {>}},
                    mark=at position .7 with {\arrowreversed {>} }
                  },
                node distance=33mm]
    \node[state]    (n1) {1};
    \node[state]    (n2) [right=of n1] {2};
    \path[->,every loop/.style={looseness=8}]
   (n1) edge [postaction={decorate}] node [pos=0.3,above] {$\alpha$}
                                     node [pos=0.7,above] {$\beta$}  (n2)
   (n1) edge [in=210,out=150,loop] node[above=11pt] {$1-\alpha$} ()
   (n2) edge [in=-30,out=30, loop] node[above=11pt] {$1-\beta$}  ();
        \end{tikzpicture}
    \end{document}

编辑：in我通过定义循环和out角度来 改变循环的外观，并简化状态之间的连接。