where L(M ) is a function of the number of model parameters (≈ the product of the number of topics and the vocabulary size) and L(D|M ) is the negative log likelihood of the data given the model.
the goal is to jointly minimize the complexity of the model and maximize the likelihood of the data given the model, and the objective can be rewritten as: Figure 2: Two possible partitioning trees for the Amazon.com Books category tree (Figure 1).