For each variable in the model stages are joined iteratively.
At each iteration the two stages with minimum distance are selected and
joined if their distance is less than thr.
Available distances are: manhattan (manhattan), euclidean (euclidean),
Renyi divergence (reny), Kullback-Liebler (kullback),
total-variation (totvar), squared Hellinger (hellinger),
Bhattacharyya (bhatt), Chan-Darwiche (chandarw).
See also probdist.