We assume that π is a K-vector (where we take the limit as K → ∞) where π k describes the population proportion of documents that contain latent feature k. We suppose that π is generated by the stick-breaking construction (Doshi-Velez et al., 2009).
we suppose that η k ∼ Beta(α, 1) for all K. We label π 1 = η 1 and for each remaining topic, we assume that π k = k z=1 η z .