[Tex/LaTex] Arrow tips in TiKZ appearing where I do not specify them

arrowsautomatatikz-pgf

In a simple drawing like this (I use automata library):

\begin{tikzpicture}[shorten >=1pt,node
  distance=2cm,auto,initial text=]
  \tikzstyle{every state}=[draw=blue!50,very thick,fill=blue!20]
  \node[state] (a) {};
  \node[coordinate] (b) [right of=a] {};
  \node[state] (c) [right of=b] {};
  \draw[-] (a) edge node {a} (b);
  \draw[->] (b) edge (c);
\end{tikzpicture}

I get a tip in node b even though I do not specify it there. I create an additional node (here: b) to have a segmented line, and I don't want any tips there. How can I get rid of that tip? Interestingly, if I put a star at the end of - as an option for \draw, I get both a filled circle and an arrow tip at b, but if I keep - option, and prepend a star to ->, I get two filled circles at b.

I don't know how to mark a comment as a good answer, but the right (and the simplest) answer was among comments. I replaced \draw[-] (a) edge with \path (a) edge[-] and draw[->] (b) edge with \path (b) edge[->]. I also had to remove the global option shorten >=1pt which gave me still small gaps in lines. What I wanted to achieve was several lines going horizontally, and then converging at various angles (with an arrow tip at the end) at a single state. Thanks for all the comments and answers.

Best Answer

To remove the tip at node b, first remove the coordinate option in that command. This will leave a short segment of space. Then use calc for calculaion of a new coordinate to fill the space by line.

enter image description here

Code: method 1

\documentclass[border=1cm]{standalone}
\usepackage{tikz}
\usetikzlibrary{automata,arrows,calc}

\begin{document}
\begin{tikzpicture}[shorten >=0pt, node distance=2cm,auto]
  \tikzstyle{every state}=[draw=blue!50,very thick,fill=blue!20]
  \node[state] (a) {};
  % method 1: remove the coordinate definition
  \node [] (b) [right of=a] {};           
  \node[state] (c) [right of=b] {};
  \draw (a) edge node{a} ($(b)+(0.2,0)$); % an extra line is drawn to fill the blank
  \draw[->] (b) edge (c);
\end{tikzpicture}
\end{document}

Edit (2014/01/23): Method 2

\documentclass[border=1cm]{standalone}
\usepackage{tikz}
\usetikzlibrary{automata,arrows}

\begin{document}
\begin{tikzpicture}[shorten >=1pt, node distance=2cm,auto]
  \tikzstyle{every state}=[draw=blue!50,very thick,fill=blue!20]
  \node[state] (a) {};
  % method 2: remove the coordinate definition and set outer sep=-4pt.
  \node[outer sep=-4pt] (b) [right of=a] {}; 
  \node[state] (c) [right of=b] {};
  \draw (a) edge node{a} (b);     % method 2: no extended draw.
  \draw[->] (b) edge (c);
\end{tikzpicture}
\end{document}
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