strict graph {
    rankdir=RL;
    splines=false;

    subgraph cluster_visible {
        label = "Visible units";
        color=grey;
        node [style=filled, color=red, fontcolor=red];
        v1; v2; v3;
    }
    subgraph cluster_hidden {
        label = "Hidden units";
        color=grey;
        node [style=filled, color=lightblue, fontcolor=lightblue];
        h3; h4; h1; h2;
    }

    h1 -- v1;
    h1 -- v2;
    h1 -- v3;
    h2 -- v1;
    h2 -- v2;
    h2 -- v3;
    h3 -- v1;
    h3 -- v2;
    h3 -- v3;
    h4 -- v1;
    h4 -- v2;
    h4 -- v3;
}