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?

Dan Rosenstark · Accepted Answer · 2019-11-21 23:23:12Z

130

You should just use:

A -> B [dir=both]

edited Nov 21, 2019 at 23:23

Dan Rosenstark

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answered Jul 19, 2013 at 9:07

user2598811

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3 Comments

Aaron Hall Over a year ago

This saved me some redundant lines, and I'm using it as well as the top answer where appropriate.

Yetti99 Over a year ago

You don't need quotes around "both"

Dan Rosenstark Over a year ago

@NoahSussman It can't be the accepted answer because it doesn't actually answer the question ;)

Jon Clements · Accepted Answer · 2019-01-17 18:49:26Z

91

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, 2019 at 18:49

Jon Clements

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answered Aug 11, 2010 at 22:24

spenthil

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5 Comments

Aaron Hall Over a year ago

Works with a label for me, and I'm running an older version.

philw Over a year ago

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.

Dan Rosenstark Over a year ago

This is silly but it's what the OP wanted, so big up!

Tropilio Over a year ago

@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?

vorburger Over a year ago

It's noteworthy that this only works if without labels, as seen e.g. with magjac.com/graphviz-visual-editor, this works and does what you want: dot digraph { concentrate=true a -> b b -> a c -> b d -> b } whereas this does not: dot digraph { concentrate=true a -> b [label="1"] b -> a [label="2"] c -> b d -> b }

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