I experimented with two Graphviz features that I thought might improve the appearance of my decision trees:

1. I wanted the connecting lines to be rectilinear rather than curvilinear. Unfortunately, I am not able to achieve this effect when I use labelled edges; rectilinear connections only works when labels are applied to nodes, when labels are applied to edges it may be more difficult to calculate line placement. Rectilinear connections might have looked better but I'll have to live with curvilinear connections because I prefer labelled edges for the decision trees I'm exploring right now.
2. I wanted to separately highlight actions, events, and outcome sections of the decision tree. I found a way to do this for the outcome nodes but have not found a way to apply further labelling or highlighting to labelled edges.

Todays blog shows how to use the "subgraph" feature of the dot language to highlite nodes that are related in some way. I used the subgraph feature to better highlite what the payoffs were for each separate action. The possible payoffs associated with each action option are distinguished by having a different color and bounding box for each set of payoffs.

Notice that the payoffs associated with each action are separately highlited and that I also add up the payoffs for each set of payoffs and report it as the expected value (EV) for that action. Here is where I get into calculating expected values manually because the dot language is not a general purpose programming language. For that I'll be using PHP in my next blog to compute expected values and supply them to the dot file that is generated.