Edge Styling in Graph funciton

Question

Inside the Graph[] command, is there a way to "spread" multiedges apart? if you have many edges they get quite close together.

Specifically, I have many small graphs with multiedges which will themselves be vertices on a large graph, and I would like to be able to see all the edges even when the graph is small.

Answer 1

I do not know if there is an easy way with Graph, unfortunately.

The older (and deprecated) GraphPlot has this feature through the MultiedgeStyle option.

One way with Graph, which only works for some graph layouts, is the following:

Graph[{1 -> 2, 1 -> 2, 1 -> 2, 1 -> 2}, EdgeShapeFunction ->
  Function[{pts, edge},
   Module[
    {stretch = 2, first = First[pts], last = Last[pts], med, mid},
    med = Median[pts];
    mid = (first + last)/2;
    Arrow@BezierCurve[{first, mid + stretch (med - mid), last}]
    ]
   ]]

Set the stretch factor to spread the multi-edges.

This method assumes that multi edges are simple arcs from the starting point to the endpoint. With GraphLayouts such as "LayeredDigraphEmbedding", or with explicitly set "EdgeLayout"s, this is not the case. Thus if you use this in a general function, I recommend setting the GraphLayout explicitly to something which generally works well, such as "SpringElectricalEmbedding".