Coherence scores for each topic's top-M words, computed from the fit's
stored document-term matrix. "mimno" is the UMass-style score of
semantic_coherence(); "npmi" averages pairwise normalized PMI; "c_v" is
the Roeder et al. (2015) measure (one-set segmentation, NPMI confirmation,
cosine aggregation). NPMI/c_v use document co-occurrence as the probability
estimator. Higher is more coherent (npmi/c_v are roughly in -1, 1).
Usage
coherence(model, measure = c("mimno", "npmi", "c_v"), M = 10L)