Derivation of the Variational Bayes Equations

The derivation of key equations for the variational Bayes approach is well-known in certain circles. However, translating the fundamental derivations (e.g., as found in Beal (2003)) to the notation of Friston (2013, 2015) is somewhat delicate. Further, the notion of using variational Bayes in the context of a system with Markov blankets requires special attention. This Technical Report presents the derivation in detail. It further illustrates how the variational Bayes method provides a framework for a new computational engine, incorporating the 2-D cluster variation method (CVM), which provides a necessary free energy equation that can be minimized across both the external and representational system's states, respectively.