Netzwerk-Flussdiagramm

\documentclass[varwidth=true, border=2pt]{standalone}

\usepackage{tikz}
\usetikzlibrary{shapes,arrows}
\begin{document}
\pagestyle{empty}


% Define block styles
\tikzstyle{decision} = [diamond, draw, fill=blue!20,
    text width=4.5em, text badly centered, node distance=3cm, inner sep=0pt]
\tikzstyle{block} = [rectangle, draw, fill=blue!20,
    text width=5em, text centered, rounded corners, minimum height=4em]
\tikzstyle{line} = [draw, -latex']
\tikzstyle{cloud} = [draw, ellipse,fill=red!20, node distance=3cm,
    minimum height=2em]

\begin{tikzpicture}[node distance = 2cm, auto]
    % Place nodes
    \node [block] (init) {initialize model};
    % \node [cloud, left of=init] (expert) {expert};
    % \node [cloud, right of=init] (system) {system};
    \node [block, below of=init] (qualitycheck) {calculate $q$};
    \node [decision, below of=qualitycheck] (decide) {is $q$ reasonable};
    \node [block, left of=decide, node distance=3cm] (investigate) {investigate};
    \node [block, below of=decide, node distance=3cm] (train) {train};
    \node [decision, below of=train] (decide2) {is $q$ good enough};
    \node [block, left of=investigate, node distance=3cm] (update) {update model};
    \node [block, below of=decide2, node distance=3cm] (stop) {stop};
    % Draw edges
    \path [line] (init) -- (qualitycheck);
    \path [line] (qualitycheck) -- (decide);
    \path [line] (decide) -- node {yes} (train);
    \path [line] (decide) -- node {no} (investigate);
    \path [line] (investigate) -- (update);
    \path [line] (train) -- (decide2);
    % \path [line] (decide) -| node [near start] {yes} (update);
    % \path [line] (update) |- (init);
    \path [line] (decide2) -- node {yes}(stop);
    \path [line] (decide2) -| node {no}(update);
    \path [line] (update) |- (init);
    % \path [line,dashed] (expert) -- (init);
    % \path [line,dashed] (system) -- (init);
    % \path [line,dashed] (system) |- (evaluate);
\end{tikzpicture}
\end{document}