"[...] C implementation of variational EM for latent Dirichlet allocation [...]"

E.g.: http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Chomsky_hierarchy.html

About: http://www.cs.princeton.edu/~blei/lda-c/

(No links in submission text: https://news.ycombinator.com/formatdoc ...)