[Tex/LaTex] Make a TikZ automata edge pass “outside ” the automata

automatatikz-pgf

I am trying to draw a Moore machine with TikZ. This is what I have so far:

\documentclass{minimal}
\usepackage{tikz}
\usetikzlibrary{arrows,automata,positioning}

\begin{document}
\begin{tikzpicture}[>=latex',shorten >=1pt,node distance=3cm,on grid,auto]
  \node[state,initial] (q0-e) {$q_0/\epsilon$};
  \node[state] (q0-1) [below right=of q0-e] {$q_0'/1$};
  \node[state] (q1-0) [above right=of q0-1] {$q_1/0$};
  \node[state] (q2-1) [below right=of q1-0] {$q_2/1$};
  \node[state,accepting] (q3-0) [below left=of q0-1] {$q_3/0$};
  \node[state,accepting] (q3-1) [below right=of q0-1] {$q_3'/1$};
  \path[->] (q0-e) edge node {a} (q1-0);
  \path[->] (q0-e) edge node {b} (q3-0);
  \path[->] (q0-1) edge node {a} (q1-0);
  \path[->] (q0-1) edge [bend right] node {b} (q3-0);
  \path[->] (q1-0) edge [bend left=90,looseness=2.5] node {a} (q3-1);
  \path[->] (q1-0) edge node {b} (q2-1);
  \path[->] (q2-1) edge node {a} (q0-1);
  \path[->] (q2-1) edge node {b} (q3-1);
  \path[->] (q3-0) edge node {a} (q3-1);
  \path[->] (q3-0) edge [bend right] node {b} (q0-1);
  \path[->] (q3-1) edge [loop below] node {a} (q3-1);
  \path[->] (q3-1) edge node {b} (q0-1);
\end{tikzpicture}
\end{document}

And it produces the automaton below:

Moore machine

But I would like to have the edge from $q_1/0$ to $q_3'/1$ to pass "outside" the automaton, like shown by the red line of the following picture:

Moore machine with line indicating the desired drawing

Can anyone show how to achieve that? Thanks.

Best Answer

For that effect, extra points are needed. Here Bezier curve is used where two extra points are located 4cm to right of points (q1-0) and (q3-1) and then command (p1) .. controls (p2) and (p3) .. (p4); is applied. Also calc from tikzlibrary is used to compute the coordinates.

enter image description here

Code

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{automata,arrows,trees,positioning,shapes,calc}
\begin{document}

\begin{tikzpicture}[>=latex',shorten >=1pt,node distance=3cm,on grid,auto]
  \node[state,initial] (q0-e) {$q_0/\epsilon$};
  \node[state] (q0-1) [below right=of q0-e] {$q_0'/1$};
  \node[state] (q1-0) [above right=of q0-1] {$q_1/0$};
  \node[state] (q2-1) [below right=of q1-0] {$q_2/1$};
  \node[state,accepting] (q3-0) [below left=of q0-1] {$q_3/0$};
  \node[state,accepting] (q3-1) [below right=of q0-1] {$q_3'/1$};
  \path[->] (q0-e) edge node {a} (q1-0);
  \path[->] (q0-e) edge node {b} (q3-0);
  \path[->] (q0-1) edge node {a} (q1-0);
  \path[->] (q0-1) edge [bend right] node {b} (q3-0);
  \path[->] (q1-0) edge node {a} (q3-1);
  \path[->] (q1-0) edge node {b} (q2-1);
  \path[->] (q2-1) edge node {a} (q0-1);
  \path[->] (q2-1) edge node {b} (q3-1);
  \path[->] (q3-0) edge node {a} (q3-1);
  \path[->] (q3-0) edge [bend right] node {b} (q0-1);
  \path[->] (q3-1) edge [loop below] node {a} (q3-1);
  \path[->] (q3-1) edge node {b} (q0-1);
  \draw [->,thick,red] (q1-0) ..  controls  ($(q1-0)+(4cm,0)$) and
  ($(q3-1)+(4cm,0)$) ..  (q3-1);
\end{tikzpicture}

\end{document}
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