# [Tex/LaTex] Code for a probability tree

tikz-pgf

A long time ago I have written a code for a probability tree (see picture below), unfortunately i lost the code. Does somebody have an idea, how i can realize it again?

I have already tried an old version but it fails

\begin{figure}[H]
\centering
\begin{tikzpicture}[line cap=round,line join=round,>=triangle 45,x=0.6cm,y=0.5cm]
\clip(0,-6.5) rectangle (18,6);
\draw [line width=2pt] (2,-1)-- (9,2);
\draw [line width=2pt] (2,-1)-- (9,-4);
\draw [line width=2pt] (9,2)-- (16,4);
\draw [line width=2pt] (9,2)-- (16,0);
\draw [line width=2pt] (9,-4)-- (16,-2);
\draw [line width=2pt] (9,-4)-- (16,-6);
\filldraw [red] (2,-1) circle (2.8pt);
\filldraw [red] (9,2) circle (2.8pt);
\filldraw [red] (9,-4) circle (2.8pt);
\filldraw [red] (16,-6) circle (2.8pt);
\filldraw [red] (16,-2) circle (2.8pt);
\filldraw [red] (16,4) circle (2.8pt);
\filldraw [red] (16,0) circle (2.8pt);
\node (A) at (9,2.8) {$V$};
\node (B) at (9,-3.2) {$\overline{V}$};
\node (C) at (16,4.8) {$S$};
\node (D) at (16,0.8) {$\overline{S}$};
\node (E) at (16,-1.2) {$S$};
\node (F) at (16,-5.2) {$\overline{S}$};
\node (G) at (5,1.5) {\scriptsize {\color{blue}$P(V)=0,4$}};
\node (G) at (5,-3.5) {\scriptsize {\color{blue}$P(\overline{V})=0,6$}};
\node (G) at (12,3.8) {\scriptsize {\color{blue}$P(S|V)=0,6$}};
\node (G) at (12,0) {\scriptsize {\color{blue}$P(\overline{S}|V)=0,4$}};
\node (G) at (12,-2) {\scriptsize {\color{blue}$P(S|\overline{V})=0,3$}};
\node (G) at (12,-6) {\scriptsize {\color{blue}$P(\overline{S}|\overline{V})=0,7$}};
\end{tikzpicture}
\caption{Baumdiagramm für Aufgabe 11}

\end{figure}

In short, to modify your code, replace all the instances where you have

\filldraw [red] (x,y) circle (2.8pt);

with

\node [draw=black,fill=red!10,circle] at (x,y) {$A$};

Except for the first red circle, that you can just remove. And of course replace $A$ with the appropriate symbol for the node in question. Here is a version of your code where I cleaned up a little bit. I didn't change the text in the nodes, but that you can manage.

\documentclass[border=5mm]{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}[line cap=round,line join=round,x=0.6cm,y=0.5cm]
\coordinate (O) at (2,-1);
\begin{scope}[every node/.style={circle,draw=black,fill=red!10}]
\node (A) at (9,2) {$V$};
\node (B) at (9,-4) {$\overline{V}$};
\node (C) at (16,4) {$S$};
\node (D) at (16,0) {$\overline{S}$};
\node (E) at (16,-2) {$S$};
\node (F) at (16,-6) {$\overline{S}$};
\end{scope}

\draw (O) -- (A) -- (C)
(A) -- (D)
(O) -- (B) -- (E)
(B) -- (F);

\begin{scope}[every node/.style={blue,font=\scriptsize}]
\node at (5,1.5) {$P(V)=0,4$};
\node at (5,-3.5) {$P(\overline{V})=0,6$};
\node at (12,3.8) {$P(S|V)=0,6$};
\node at (12,0) {$P(\overline{S}|V)=0,4$};
\node at (12,-2) {$P(S|\overline{V})=0,3$};
\node at (12,-6) {$P(\overline{S}|\overline{V})=0,7$};
\end{scope}
\end{tikzpicture}
\end{document}

# TikZ tree

However, this is a tree, so you could also use the tree drawing capabilities of TikZ, as such:

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

\begin{document}
\begin{tikzpicture}[
circ/.style={draw=black,fill=red!15,circle},
grow=right,
level 1/.style={sibling distance=2cm},
level 2/.style={sibling distance=1cm},
level distance=3cm]
\node [coordinate] {}
child {
node[circ] {$\bar{A}$}
child { node[circ] {$\bar{D}$}
edge from parent
node [below=2] {$0.9999$}}
child { node[circ] {$D$}
edge from parent
node [above=2] {$0.0001$}}
edge from parent
node [below=2] {$0.9999$}
}
child {
node[circ] {$A$}
child { node[circ] {$\bar{D}$}
edge from parent
node [below=2] {$0.0001$}}
child { node[circ] {$D$}
edge from parent
node [above=2] {$0.9999$}
}
edge from parent
node [above=2] {$0.0001$}
};
\end{tikzpicture}
\end{document}

# forest

Or using the more powerful forest package, which is rather popular I think. I'm no expert though, so it's quite possible the edge labels could be solved more elegantly.

\documentclass[border=5mm]{standalone}
\usepackage{forest}
\begin{document}
\begin{forest}
for tree={
math content,
if n=0{coordinate}{circle,draw=black,fill=red!10},
grow=0,
l=3cm
}
[
[\overline{A},edge label={node[midway,below=2pt]{0.9999}}
[\overline{D},edge label={node[midway,below]{0.9999}}]
[D,edge label={node[midway,above]{0.0001}}]
]
[A,edge label={node[midway,above=2pt]{0.0001}}
[\overline{D},edge label={node[midway,below]{0.0001}}]
[D,edge label={node[midway,above]{0.9999}}]
]
]
\end{forest}
\end{document}