Double arrow in TikZ?

Question

I'm trying to draw two arrows between nodes as follows:

A ------> B
  <--/---

The arrows should be parallel, in opposite directions but not on top of each other. (I can bend the arrows but that's not what I'm after.)

What's the cleanest way to do this in TikZ? And can I have just one of the arrows "struck out" as in the example?

Answer 1

With PSTricks. Unfortunately, no option to change the radius of \circlenode to be uniform.

\documentclass[pstricks,border=12pt]{standalone}
\usepackage{pst-node}
\psset{arrows=->,arrowinset=0}
\begin{document}
\begin{pspicture}[showgrid](5,2)
    \rput(1,1){\circlenode{Left}{left}}
    \rput(4,1){\circlenode{Right}{right}}
    \ncline[offset=5pt]{Left}{Right}
    \ncline[offset=5pt]{Right}{Left}
    \ncput{\psline[arrows=-](5pt;45)(5pt;-135)}
\end{pspicture}
\end{document}

Answer 2

Here is an idea that might answer both your questions. It uses yshift to move the start and end points of the two paths up/down by 5pt. The result could be further improved by shifting the start/end points along the x axis in order for the paths to really be in contact with the nodes' circles.

A custom TikZ style is used to add a strike-through marking at the middle of the second path. This could be parameterized further to allow moving the marking to any position on the path etc.

I cannot tell whether this is the most elegant solution though.

\documentclass{minimal}

\usepackage{tikz}

\usetikzlibrary{decorations,decorations.markings}

\tikzset{
  strike through/.style={
    postaction=decorate,
    decoration={
      markings,
      mark=at position 0.5 with {
        \draw[-] (-5pt,-5pt) -- (5pt, 5pt);
      }
    }
  }
}

\begin{document}
\begin{tikzpicture}
  \node[draw,circle] (foo) at (0,0) { foo };
  \node[draw,circle] (bar) at (4,0) { bar };

  \draw[>=latex,->]                ([yshift= 5pt] foo.east) -- ([yshift= 5pt] bar.west);
  \draw[>=latex,<-,strike through] ([yshift=-5pt] foo.east) -- ([yshift=-5pt] bar.west);
\end{tikzpicture}
\end{document}

Here is how it looks like: