title: creating a layout for graph nodes with constraints
body: <p>I want to draw a graph. However, I have some constraints about the layout of nodes. namely, the y coordinate of each node is given in advance, and cannot be moved. I want to find suitable x coordinate for each node, so that there will be no/minimal crossing when drawing the (straight) edges of the graph. I know it will not be always possible, but my graphs are likely be rather sparse, so I believe that in practice this will be possible.</p>
  
  <p>Any suggestion regarding how to approach this, hopefully with the igraph package which I use, but I'm flexible if you have other suggestions.</p>
  
  <p>No example because this a rather generic question about generating layouts.</p>