title: Plot several graphs with R igraph
body: <p>I would like to draw two graphs <code>g1</code> and <code>g2</code> on the same plot with the <code>R</code> version of <code>igraph</code>. However, if I just apply the <code>plot</code> (or <code>plot.igraph</code>) function twice, I just get two separate plots. Is there a way to have both graphs drawn on the same plot?</p>
  
  <p>Here's some minimal code:</p>
  
  <pre><code>library(igraph)
  g1 &lt;- barabasi.game(10)
  g2 &lt;- barabasi.game(5)
  plot(g1)
  plot(g2)
  </code></pre>
  
  <p>Edit: I want both graphs to be plotted in the same figure. So, one node from <code>g1</code> and another one from <code>g2</code> could very well overlap in this figure, if they hold close spatial positions in their respective graphs.</p>