How to show arrows symmetrically for self-loops in a dot graph

Question

I am working with a DFA which I have described in the dot file format. One of the nodes in my DFA has two self-loops, which I originally described with the following way

digraph {
  rankdir=LR;
  a -> a [color=blue]
  a -> a [color=green]
}

Which produces this output when I run dot graph.gv -Tpng

For symmetry reasons, I'd like to have the blue and the green arrows on opposite sides of the node. I can modify the headport and tailport of the green arrow to force it to start from the bottom of the node as follows:

digraph {
  rankdir=LR;
  a -> a [color=blue]
  a:sw -> a:se [color=green]
}

Unfortunately, that produces an absolutely wonky output:

What's the correct way of getting the two arrows to be symmetrically opposite each other on the node?

Answer 1

I doubt you have a lot of control over the edge layout. But you can experiment with the headport attribute values. Here are some examples.

Example 1

digraph {
  rankdir=LR;

  a:n -> a [color=blue]
  a:s -> a [color=green headport=center]
}

View in editor

Example 2

digraph {
  rankdir=LR;

  a:ne -> a [color=blue]
  a:sw -> a [color=green headport=center]
}

View in editor

---

Other layouts

You can also experiment with different layouts. Here are some options for the circo layout.

Example 3

digraph {
  rankdir=LR;
  layout="circo"

  a:n -> a:_ [color=blue headport=n]
  a:s -> a:_ [color=green headport=s dir=back]
}

View in editor

Example 4

digraph {
  rankdir=LR;
  layout="circo"

  a:nw -> a:w [color=blue headport=_]
  a:se -> a:e [color=green headport=_]
}

View in editor