Dirichlet distribution

A few months ago, I built a recommender system that employed topic modelling to display relevant tasks to employees. The algorithm used was Latent Dirichlet Allocation (LDA), a generative model that has been around since the early 2000s¹. Of course, I didn't rewrite LDA from scratch but used the implementation in Python's scikit-learn. But it started me thinking about the sequence of research that lead to the creation of the LDA model. The problem with such libraries is that it's all too easy to include a few lines in your code and just move on, so I dug out my old machine learning books with the goal of knowing enough to be able to explain LDA in all its gory probabilistic detail.