A Poisson distribution models how many events occur in a fixed interval when their average rate is specified. In latent Dirichlet allocation (LDiA), it supplies the document’s generated word count: one parameter sets the average document length. section 4.5.1
Generating documents
A document-generation process first draws its word count from a Poisson distribution, then draws a topic mixture from a Dirichlet distribution and selects words until that count is reached. For a comments corpus, the observed mean length is about 54.21 tokens. section 4.5.1






