Experimentation with learning a generative model for classes of trees with variable width, depth, and branching factor using a directed heirarchy of Markov random fields (semi-restricted Boltzmann machines).
See http://www.cs.toronto.edu/~hinton/absps/lateral.pdf for background details.
Credit The code used here is originally based off of ref work by Ruslan Salakhutdinov and Geoff Hinton. The original disclaimer included with the code follows:
Code provided by Ruslan Salakhutdinov and Geoff Hinton
Permission is granted for anyone to copy, use, modify, or distribute this program and accompanying programs and documents for any purpose, provided this copyright notice is retained and prominently displayed, along with a note saying that the original programs are available from our web page. The programs and documents are distributed without any warranty, express or implied. As the programs were written for research purposes only, they have not been tested to the degree that would be advisable in any important application. All use of these programs is entirely at the user's own risk.