Graphviz FAQ 2001-02-10

Note: This is not a tutorial; to understand this you should know how to use the basic features of the tools and languages involved. Please see the user guides for further information.

General

See Dot.ref.

Q. Where can I discuss graphviz?

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Q. I'm trying to make a dot layout larger. How?

Magnification isn't directly supported. We admit this should be fixed. For now you have to adjust individual parameters fontsize, nodesep and ranksep. For example

           digraph G {
                graph [fontsize=24];
                edge  [fontsize=24];
                node  [fontsize=24];
                ranksep = 1.5;
                nodesep = .25;
                edge [style="setlinewidth(3)"];
                a -> b -> c;
           }

If you're using Postscript, you can just scale up the output by manually adding a command such as 2 2 scale where the Postscript environment is set up. Make sure to adjust the BoundingBox too if your tools look at this header.

Q. I'm trying to make a neato layout larger. How?

See above regarding font sizes.

You can generally push nodes further apart by changing elen (edge lengths). For example, to make it three times the default:

        graph G {
           edge [len=3]
           a -- { b c d }
        }

Clusters

This only works in graphviz version 1.7 and higher. To make edges between clusters, first set the graph attribute compound=true. Then, you can specify a cluster by name as a logical head or tail to an edge. This will cause the edge joining the two nodes to be clipped to the exterior of the box around the given cluster.

For example,

      digraph G {
        compound=true;
        nodesep=1.0;
        subgraph cluster_A {
          a -> b;
          a -> c;
        }
        subgraph cluster_B {
          d -> e;
          f -> e;
        }
        a -> e [ ltail=cluster_A,
                 lhead=cluster_B ];
      }

        a -> e [ltail=cluster_A];

Q. Clusters are hard to see.

Set bgcolor=grey (or some other color) in the cluster.

Output features

It's not us! It's probably your printer setup. If you don't believe this, run dot -Tps and looks for the tBoundingBox header. The coords are in 1/72ths of an inch.

Q. How do I create special symbols and accents in labels?

The following solution only works with the raster drivers that load Truetype or Type1 fonts! (That means, -Tgif, -Tpng, -Tjpeg, and possibly -Tbmp or -Txbm if enabled). Use UTF8 coding, e.g. ¥ for the Yen currency symbol. Example: graph G { yen [label="¥"] }

You can look up other examples in this handy character set reference .

Q. How do I get font and color changes in record labels or other labels?

There's no easy way right now. We're working on it. Sigh.

Q. In plain format, arrowheads are missing. It's a bug that may have solidified into a feature by now. A workaround is to set

      edge [dir=none]

Q. When I have a red edge it shows up as a solid red in PNG and GIF formats, but has a black border when rendered to JPEG.

This is an artifact of JPEG's lossy compression algorithm. JPEG isn't very good for line drawings. PNG is bitmap format of choice. John Ellson wants to deprecate and eventually remove the JPEG driver, but North is reluctant to change anything that people might already rely on.

Q. How can I get custom shapes in my graph?

Please see the Shape HowTo for some approaches. There is no easy way to create custom shapes that work with dot/neato, dotty (Unix or MS-Windows) and Grappa (the Java front end), because they don't share any universal back end structure. We're thinking about it.

Q. How can I get in dotty?

If it's not there already, there's probably no easy way to do it except by rolling up your sleeves and hacking the dotty (lefty script) code that interprets and renders graphical attributes. This is problematic for the same reason as above: there's no universal low-level driver layer that is shared across all the graphviz tools. Sorry, we already feel bad about it.

Q. I already have all the coordinates for the nodes and edges of my graph and just want to use dot, neato, or dotty to render it. How?

Put the graph with layout attributes into a dot file. Then run neato -s -nop, for example:

neato -s -nop -Tgif file.dot -o file.gif

Q. I already have all the coordinates for the nodes, and I want dot or neato to route the edges.

It's not really too convenient to use dot for this

Q. I already have all the coordinates for the nodes and edges of my graph and just want to use dotty to render it. How?

Problems

neato -Goverlap=false

Q. How can I avoid node-edge overlaps in neato?

neato -Goverlap=false -Gsplines=true -Gsep=.1

The sep argument is the node-edge separation as
a ratio of a node's bounding box. (Don't ask why this
isn't just a constant!)  Note that this option really
slows down neato, so should be used sparingly and only
with modest-sized graphs.

Q. Neato runs forever on a certain example.

It could be that your graph is too big, or it could be
that neato is cycling.
Run neato -v to observe its progress.
If your graph is small, we have a bug - neato needs an anti-cycling heuristic.
To defeat the bug, you can force neato to run differently to stop earlier
by tactics such as:
neato -Gstart=rand
neato -Gepsilon=.01
neato -Gmaxiter=500


If it's a large example, the problem is that neato (which is nearly the same
algorithm as multidimensional scaling) iis at least quadratic in time
complexity.  The spline router is even worse: O(N^3).  So don't run neato -Groutesplines=true unless you're willing to pay for it.

Q. Dot runs forever on a certain example.

Try dot -v to observe its progress.

Try 

Note that it's possible to make graphs whose layout or even parsing
is quadratic in the input size. For example, in dot, 

digraph G {
    a -> b -> c -> .... -> x -> y -> z
    a -> z
    b -> z
    c -> z
    /* and so on... */
	x -> z
}


The total edge length (therefore the layout time) of
this as a ranked graph is quadratic in the number of nodes.


You probably won't encounter the following, but it is also possible
to construct graphs whose parsing takes quadratic time, by appending
attributes to nodes and edges after the graph has been loaded.
For example:

digraph G {
    /* really big graph goes here... */
    n0 -> n1 -> ... -> n999999999;

    n0 [attr0="whatever"]
    n0 [attr1="something else"]
    /* and so on with many more attributes */
}

The addition of attr0 touches every node of the graph.
Then the addition of attr1 touches every node again, and so on.