alternatively update Q_{\miu} and Q_{\sigma}
another example is the spin system:
a nasty thing here is the coupling term in E(x;J)
and we use another decoupling Q(x;a) to fit
two spin system example:
less on {-1,1} and {1,-1}, higher on {-1,-1} and {1,1}
[Information Theory] L14: Approximating Probability Distributions (IV): Variational Methods
原文：https://www.cnblogs.com/ecoflex/p/10880795.html