fst-train is used to learn statistical weights for the transducers transitions based on training data.
Training is either unsupervised (default) or supervised (option -b).
In supervised mode, the input contains fully disambiguated data with the surface and the analysis form.
The format restrictions are identical to those applying for lexicon entries, i.e. all operators other
than the colon operator (:) are interpreted literally.
In unsupervised mode, the input data consists of surface strings. The format is identical to the input
format of fst-infl and fst-infl2.
The transducer weights are stored in files whose names are obtained by appending .prob to the names of
the transducer files.