After learning expectation-propagation (EP) from PRML, I think it is possible to program EP algorithms designed for inference in factorized graphical models using GBR. However, the following issues are to be confirmed:
- There has no proof that EP converges to a (local or global) optima. However, the EP algorithm developed for LDA  seems converges.
- The EP for LDA  is in fact an extended EP algorithm, but not literally an EP algorithm. Need to make sure that this extended EP can be programmed using GBR.
- Need to estimate the number and size of messages need to passed between workers. This is an approximate estimate of the communication cost of the GBR program.
- Thomas Minka and John Lafferty, Expectation-propagation for the generative aspect model, UAI 2002