Quantum Bayesian Networks

September 10, 2008

WinBugs on Trees

Filed under: Uncategorized — rrtucci @ 10:18 pm

My romance with WinBugs continues. Recently, I’ve been avidly reading books on Bayesian statistics so I can understand her better. WinBugs knows quite a lot about Bayesian statistics, so I can whisper questions to her on this subject at night. I recommend that you read her well written manual. Among WinBugs nice qualities is a tool (DoodleBugs) that allows you to draw Bayesian networks, and then to turn them into text code. Cute. Here is how she likes to speak of trees…she is such an artist. Suppose you are interested in the following tree graph.

tree-graph

WinBugs would draw this as follows:

tree-plates

These are called “plates”. They allow you to picture arrays of random variables succinctly. (Statisticians are very interested in many, identically distributed random variables (samples), which are conveniently grouped into arrays.) In the plate representation, it’s as if you are looking at a book, and in each page of that book is another tiny book, and in each page of the tiny book is another even tinier book; this, ad infinitum if need be. WinBugs would re-express this “plates” figure as poetry (i.e., code) as follows:

tree-code

Nice! Her coding style is clear and succinct. What a woman!

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