Messy flowchart using tikz

Question

I have a beamer slide:

\documentclass{beamer}

\usepackage{tikz}
\usetikzlibrary{shapes,arrows}

\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]

\begin{document}

\begin{frame}{Simulated Annealing (SA)}
  \begin{center}
    \resizebox{0.4 \linewidth}{!}{%
      \begin{tikzpicture}[node distance = 2cm, auto]
        \node[block]                  (init){Init $n=0$, $T_0$, and $S_0$};
        \node[block, below of=init]   (nbrh){$S_{n+1}=N(S_n)$};
        \node[decision, below of=nbrh](ovgt){$f(S_{n+1}) \le f(S_n)$};
        \node[block, below of=ovgt]   (accp){Accept $S_{n+1}$};
        \node[decision, right of=ovgt](rand){Accept with $P = e^{-\frac{\Delta f}{t_n}}$};
        \node[block, right of=nbrh, anchor=west]   (rejj){Reject $S_{n+1}$};
        \node[block, below of=accp]   (incr){$T_{n+1} = K(T_n)$ and $n=n+1$};
        \node[block, below of=incr]   (stop){Stop};
        \node[decision, left of=stop] (stcd){Stop?};

        \path[line] (init) --          (nbrh);
        \path[line] (nbrh) --          (ovgt);
        \path[line] (ovgt) -- node{yes}(accp);
        \path[line] (ovgt) -- node{no} (rand);
        \path[line] (rand) -- node{no} (rejj);
        \path[line] (rejj) --          (nbrh);
        \path[line] (rand) |- node{yes}(accp);
        \path[line] (accp) --          (incr);
        \path[line] (incr) --          (stcd);
        \path[line] (stcd) -- node{yes}(stop);
        \path[line] (stcd) |- node{no} (nbrh);
      \end{tikzpicture}%
    }%
  \end{center}
\end{frame}

\end{document}

which gives:

There are a few things I'm not happy with in the output:

1. Simple equations like $S_{n+1}=N(S_n)% should be on 1 line. It's okay for the text to be smaller. Similarly, $T_{n+1}=K(T_n)$ should be on 1 line, 'and' can be on it's own line, and $n=n+1$ should be on it's own line. The inequality in the decision should also be on one line.

2. The vertical 'no' line connecting the "Accept" decision on the right, and the "Reject" action is not quite vertical. Also, this decision is larger than the decision immediately to the left.

3. There is very little space between these two decisions.

4. The "Accept" action under the inequality decision overlaps with the decision above. In contrast, that decision is quite far from the action above that.

5. Lastly, I'm not happy with the bottom two elements. I would have preferred to have the "Stop?" decision directly underneath, and the "Stop" action to the right. Unfortunately, I'm not sure how to put 2 bends in the "no" from "Stop?", meaning that the line actually cuts through everything above. I tried |-| and -|- but this doesn't work.

I asked a previous question here about scaling the whole tikzpicture to the height of the slide, however the solution that was presented did not work for me. It is still being cut off at the bottom. The problem may have to do with the fact that my actual beamer presentation uses the Hannover theme, and as such there is less usable space in the slide? I have gotten around it by using 0.4 \linewidth temporarily.

Answer 1

Some problems are avoided if you use the positioning library. You need to use the option on grid, you can modify locally the node distance. The width of the diamond node is not the same that the width of the rectangle, so you need to place the rectangle above the diamond if you want a vertical edge.

\documentclass{scrartcl}

\usepackage{tikz}
\usetikzlibrary{shapes,arrows,positioning}

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

\begin{document}

  \begin{center}
    \resizebox{0.4 \linewidth}{!}{%
      \begin{tikzpicture}[node distance = 2cm, auto]
        \node[block]                                (init) {Init $n=0$, $T_0$, and $S_0$};
        \node[block, below= of init]                (nbrh) {$S_{n+1}=N(S_n)$};
        \node[decision, below= of nbrh]             (ovgt) {$f(S_{n+1}) \le f(S_n)$};
        \node[block, below=2.5cm of ovgt]           (accp) {Accept $S_{n+1}$};
        \node[decision, right= 3.5cm of ovgt]       (rand) {Accept with $P = e^{-\frac{\Delta f}{t_n}}$};
        \node[block, above=3cm of rand]             (rejj) {Reject $S_{n+1}$};
        \node[block, below= of accp]                (incr) {$T_{n+1} = K(T_n)$ and $n=n+1$};
        \node[decision, below=2.5cm of incr]              (stcd) {Stop?};  
        \node[block, right=3cm of stcd]                (stop) {Stop};


        \path[line] (init) --          (nbrh);
        \path[line] (nbrh) --          (ovgt);
        \path[line] (ovgt) -- node{yes}(accp);
        \path[line] (ovgt) -- node{no} (rand);
        \path[line] (rand) -- node{no} (rejj);
        \path[line] (rejj) --          (nbrh);
        \path[line] (rand) |- node{yes}(accp);
        \path[line] (accp) --          (incr);
        \path[line] (incr) --          (stcd);
        \path[line] (stcd) -- node{yes}(stop);
        \path[line] (stcd) -- ++(-2,0) |- node[pos=.25]{no}  (nbrh);
      \end{tikzpicture}%
    }%
  \end{center}


\end{document}

Answer 2

My solution is similar to the last edit of Altermundus (I was too slow), but I address the problem of having equations in one line only. Moreover, instead of adopting \resizebox, I preferred \scalebox from the graphicx package.

Here is the code:

\documentclass{beamer}
\usepackage{lmodern}
\usepackage{graphicx}

\usepackage{tikz}
\usetikzlibrary{shapes,arrows,positioning}

\tikzset{decision/.style={diamond, draw, fill=blue!20, text width=4.5em, text badly centered, inner sep=0pt}}
\tikzset{block/.style={rectangle, draw, fill=blue!20, text width=5em, text centered, rounded corners,
 minimum width=3.5cm}}
\tikzset{line/.style={draw, -latex}}

\begin{document}

\begin{frame}{Simulated Annealing (SA)}
\begin{center}
\scalebox{0.6}{
      \begin{tikzpicture}[node distance=2.3cm]
        \node[block]                  (init){Init $n=0$, $T_0$, and $S_0$};
        \node[block, below of=init]   (nbrh){\footnotesize{$S_{n+1}=N(S_n)$}};
        \node[decision, below of=nbrh](ovgt){\footnotesize{$f(S_{n+1}) \le f(S_n)$}};
        \node[block, below of=ovgt]   (accp){Accept $S_{n+1}$};
        \node[decision, right=2cm of ovgt](rand){Accept with $P = e^{-\frac{\Delta f}{t_n}}$};
        \node[block,  above of=rand]   (rejj){Reject $S_{n+1}$};
        \node[block, below of=accp]   (incr){\scriptsize{$T_{n+1} = K(T_n)$} \\[1ex] and\\ \scriptsize{$n=n+1$}};       
        \node[decision, below of=incr] (stcd){Stop?};
        \node[block, right= 2cm of stcd]   (stop){Stop};
        % invisible node helpful later
        \node[left=1cm of accp,scale=0.05](inv){};

        \path[line] (init) --          (nbrh);
        \path[line] (nbrh) --          (ovgt);
        \path[line] (ovgt) -- node[left]{yes}(accp);
        \path[line] (ovgt) -- node[above]{no} (rand);
        \path[line] (rand) -- node[right]{no} (rejj);
        \path[line] (rejj) --          (nbrh);
        \path[line] (rand) |- node[below]{yes}(accp);
        \path[line] (accp) --          (incr);
        \path[line] (incr) --          (stcd);
        \path[line] (stcd) -- node[below]{yes}(stop);
       \path[-,draw] (stcd) -| node{} (inv.north);
       \path[line]{} (inv.north) |- node[above]{no} (nbrh);
      \end{tikzpicture}%
}      
\end{center}
\end{frame}

\end{document}

which gives:

Answer 3

You might find using a \matrix[matrix of nodes] for this easy, because then you can move around the nodes. That leaves drawing the paths which is boring no matter what.

To prohibit line breaks in math-mode, you could set \binoppenalty and \relpenalty to high values.

Example of the above (I've cut some corners with the path drawing):

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{matrix,shapes,arrows}

\tikzset{
  % re-usability is the key to happiness
  >=triangle 45,
  flowchart/.style={
    matrix of nodes,
    nodes=block,
    row sep=2\normalbaselineskip,
    column sep=3em,
  },
  block/.style={
    %font=\scriptsize, % <- that'd change font size
    draw,
    fill=blue!20,
    minimum height=3\normalbaselineskip,
    text width=7em,
    text badly centered,
    rounded corners,
    execute at begin node={
      \hskip0pt
      \binoppenalty=10000 % make it bad to break math line
      \relpenalty=10000},
  },
  decision/.style={% inherits from block via matrix
    diamond,
    sharp corners,
    inner sep=1pt,
  }
}

\begin{document}
\begin{tikzpicture}
  \matrix[flowchart] (fc) {
    Init $n=0$, $T_0$, and $S_0$ \\
    $S_{n+1}=N(S_n)$ & Reject $S_{n+1}$ \\
    |[decision]| $f(S_{n+1})\leq f(S_n)$ &
    |[decision]| Accept with $P=e^{-\frac{\Delta f}{t_n}}$ \\
    Accept $S_{n+1}$ \\
    $T_{n+1}=K(T_n)$ and $n=n+1$ \\
    |[decision]| Stop? & Stop \\
  };
  \begin{scope}[->]
    \draw (fc-1-1) -- (fc-2-1) edge (fc-3-1);
    \draw (fc-2-1) -- (fc-3-1) edge node[above] {no} (fc-3-2);
    \draw (fc-3-2) edge node[right] {no} (fc-2-2) |- node[below] {yes} (fc-4-1);
    \draw (fc-2-2) -- (fc-2-1);
    \draw (fc-3-1) -- node[right] {yes} (fc-4-1);
    \draw (fc-4-1) -- (fc-5-1) edge (fc-6-1);
    \draw (fc-6-1) edge node[above] {yes} (fc-6-2) -- +(-3,0) node[below] {no} |- (fc-2-1);
  \end{scope}
\end{tikzpicture}
\end{document}

(There's a small flaw in the first no-branch, I'll leave it as an exercise ;-).)