概率树问题

Question

我正在尝试用 LaTeX 制作这个概率树：

我尝试使用该tikz软件包，但一直遇到一些问题。这是我目前为止得到的最好的软件包（链接：https://www.writelatex.com/855538qcgkps#/1917915/)：

    \documentclass{article}

    \usepackage{tikz}
    \usetikzlibrary{trees}

    \begin{document}
    \pagestyle{empty}

    \tikzstyle{level 1}=[level distance=3cm, sibling distance=3cm]
    \tikzstyle{level 2}=[level distance=3.5cm, sibling distance=2cm]

    \tikzstyle{bag} = [circle, minimum width=10pt, inner sep=2pt]
    \tikzstyle{end} = [circle, minimum width=3pt, fill, inner sep=0pt]

    \begin{tikzpicture}[grow=right, sloped]

    \node[bag]{}
    child {
            node[bag] {O}        
                child {
                    node[end, label=right:{O}] {}
                    edge from parent
                    node[above] {}
                    node[below]  {$1-\lambda$}
                    child {
                    node[end, label=right: {O ...}] {}
                    edge from parent
                    node[above] {}
                    node[below]  {$1-\lambda$}
                }
                child {
                    node[end, label=right: {S ...}] {}
                    edge from parent
                    node[above] {$\lambda$}
                    node[below]  {}
                }
                }
                child {
                    node[end, label=right: {S}] {}
                    edge from parent
                    node[above] {$\lambda$}
                    node[below]  {}
                }
                edge from parent 
                node[above] {}
                node[below]  {$1-\lambda$}
        }
        child {
            node[bag] {S}        
            child {
                 edge from parent
                    node[above] {1}
                    node[below]  {}
                    node[bag] {O'}   
                            child {
                                    edge from parent
                                    node[above] {$1$}
                                    node[below] {$$}
                                    edge from parent
                    }
                    }
            edge from parent         
                node[above] {$\lambda$}
                node[below]  {}
        };


    \end{tikzpicture}
    \end{document}

正如您所看到的，它们完全不同，但我似乎无法继续前进，您能帮助我吗？我似乎无法意识到错误是什么。

最好的。

Answer 1

我建议你使用强大的forest包（基于 PGF/TikZ 构建）：

\documentclass{article}
\usepackage{amsmath}
\usepackage{forest}

\tikzset{
  dot/.style={circle,draw,inner sep=1.2,fill=black},
}

\newcommand\Labeli{%
  node[below left,midway,xshift=3pt,font=\small]{$(1-\lambda)$}
  node[above right,midway,xshift=-3pt,font=\small]{$0$}%
}
\newcommand\Labelii{%
  node[above left,midway,xshift=3pt,font=\small]{$S$}
  node[below right,midway,xshift=-3pt,font=\small]{$(\lambda)$}%
}
\newcommand\Labeliii{%
  node[above,midway,font=\small]{$0'$}
  node[below,midway,font=\small]{$(1)$}%
}

\begin{document}

\begin{forest}
[ ,name=a,for tree={s sep=60pt,l sep=2cm,dot,grow=0},
  [ ,name=b,edge label={\Labeli}
    [ ,name=c,edge label={\Labeli}
      [ ,name=d,edge label={\Labeli} ]
      [ ,name=e,edge label={\Labelii} ] 
    ]
    [ ,edge label={\Labelii}
      [ ,name=f,edge label={\Labeliii} ]
    ]   
  ]
  [ ,edge label={\Labelii}
    [ ,edge label={\Labeliii}
      [ ,name=g,edge label={\Labeliii} ]
    ]
  ]
]
\foreach \Nodo in {d,e,f,g}
  \node[anchor=west,xshift=3pt] at (\Nodo) {$\cdots$};
\node[yshift=-1cm,name= tiii,font=\small] at (d) {$t+3$};
\node[name= tii,font=\small] at (c|-tiii) {$t+2$};
\node[name= ti,font=\small] at (b|-tiii) {$t+1$};
\node[name= t,font=\small] at (a|-tiii) {$t$};
\end{forest}

\end{document}