Multiple directed edges igraph
<p>I would like to express the edges between vertices 1 and 2 in the following graph as two separate edges with arrows in opposite directions.  </p>

<pre><code>require(igraph) 
e &lt;-  c(1,2, 2,3, 3,1, 3,4 , 4,1 , 2,1)
g &lt;- graph(e, n=5, directed = TRUE)
tkplot(g, layout=layout.circle )
</code></pre>

<p>What I get is just one edge with an arrow on both ends. It should be easy but I haven't found it anywhere and can't figure it out. Any idea? </p>