Position a node to the right of a subgraph with graphviz

Question

I'm using graphviz to plot the DAG of a simple latent variable model:

digraph G {

    splines=line;

    subgraph cluster {
        node [style=filled, shape=circle];
        edge [color=blue]
        z[fillcolor=white, color=black, pos = "0,0!"]
        z -> x;
    }

    theta[label = "θ", shape=circle, pos = "10,0!"]
    edge [color=black, style="dashed"]
    theta->z
    theta->x

}

The output is decent:

but I'd like θ to be at the same height as z. Is that possible? I tried to use the pos attribute, but as you see, it's nicely ignored. I'm working in HackMD.

Answer 1

You can add constraint=false attribute to your theta edges so they won't affect layout and nodes will remain side by side:

digraph G {

    splines=line;

    subgraph cluster1 {
        node [style=filled, shape=circle];
        edge [color=blue]
        z[fillcolor=white, color=black, pos = "0,0!"]
        z -> x;
    }
    theta[label = "θ", shape=circle, pos = "10,0!"]
    edge [color=black, style="dashed"]
    theta -> z [constraint=false]
    theta -> x [constraint=false] // actually this one is unnecessary, may be omited in this example

}

Also, you may experiment with edge direction (e.g. change places a->b, b->a), this sometimes helps with positioning clusters.