Dot graph language - how to make bidirectional edges automatically?

Question

Here is a very simplified example of my Dot graph:

strict digraph graphName {
A->B
B->A
}

This creates alt text

Instead I want a single edge shown between A and B but with a double arrow head. I know how to get the double arrowhead as a global option:

strict digraph graphName {
  edge [dir="both"]
A->B
B->A
}

But that looks very ugly, and not all of my edges should be dual headed.

alt text

If I do more processing of the graph and detect the double reference myself and replace the two edges with a single edge, it looks OK. But I'd rather not have to do this extra step

strict digraph graphName {
A->B [dir="both"]
}

alt text

Any better solutions?

score 107 · Answer 1 · edited Nov 21 '19 at 23:23

107

You should just use:

A -> B [dir=both]

edited Nov 21 '19 at 23:23

Dan Rosenstark

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answered Jul 19 '13 at 09:07

user2598811

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This saved me some redundant lines, and I'm using it as well as the top answer where appropriate. – Aaron Hall Apr 25 '14 at 20:21
2

You don't need quotes around "both" – Yetti99 Dec 21 '18 at 20:27
@NoahSussman It can't be the accepted answer because it doesn't actually answer the question ;) – Dan Rosenstark Nov 21 '19 at 21:47

score 71 · Accepted Answer · edited Jan 17 '19 at 18:49

71

How about 'concentrate=true'?:

strict digraph graphName {
concentrate=true
A->B
B->A
}

with concentrate=true

From the documentation:

If true, use edge concentrators. This merges multiedges into a single edge and causes partially parallel edges to share part of their paths. The latter feature is not yet available outside of dot.

edited Jan 17 '19 at 18:49

Jon Clements

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answered Aug 11 '10 at 22:24

spenthil

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Works with a label for me, and I'm running an older version. – Aaron Hall Apr 25 '14 at 19:59
1

If it helps... this didn't work for me, in so much as it coalesced the edges, but only put a single arrow on the end. Then I tried to "strict digraph"... and it works perfectly then. – philw Mar 19 '15 at 13:48
This is silly but it's what the OP wanted, so big up! – Dan Rosenstark Nov 21 '19 at 23:22
@philw It does not work for me either, I get edges with a single arrowhead only. I am using pygraphviz, and I tried `pgv.AGraph(directed=True, strict=True)`, but it does not work either, i get two edges again... Any suggestions? – Tropilio Apr 28 '20 at 15:40

Dot graph language - how to make bidirectional edges automatically?

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