Implementation of the variational inference algorithms for probabilistic PCA and mixtures of probabilistic PCAs as found in:
- Bishop, Christopher M. "Variational principal components." (1999): 509-514.
- Bishop, C.M. and Winn, J.M., 2000, June. Non-linear Bayesian image modelling. In European Conference on Computer Vision (pp. 3-17). Springer, Berlin, Heidelberg.