Search for a graph package - see link

G?bor Cs?rdi schrieb:

The would prefer two parallel arrows one for each direction.
    

You can set 'curved' to a value close to zero and then the arrows will
be only a bit curved.

  

No I am lost ... do you mean?
...
E(g)$curved <- 0.5
...
plot.igraph(g, layout=layout.kamada.kawai, vertex.label.font=2)
I do not see any change ..
and I do not found any curved assignment in the plot.igraph function.

Its a very
 long mathematical formula to display those arrows, depending on the radius
of the circles, and there is a ...hidden...error in the formula.
    

I am a bit lost. What formula are we talking about?
  

http://www.equine-science.de/temp/r-graph.jpg
I tried to get the starting point of the arrows depending on the 
distance arrow-centerline node1/node2 and between the  tangent 
right-angled to the centerline  of both nodes automatically for all nodes.
(I hope you can understand my translated mathematics description...)
That's exactly what the team would like to get.

Regards Knut