Utilities for OpenFst
---------------------
Benoit Favre <benoit.favre@lif.univ-mrs.fr>
released under Apache License Version 2.0

This is a set of useful programs for manipulating Finite State Transducer with the OpenFst library.

* fstcompile-nolex [-t]: compile an acceptor [transducer], generate symbol lexicons on the fly and save them with the fst. Useful for quick hacks on a single fst.

* fstcompose-maplex <fst1> <fst2>: compose after mapping symbol tables (for use with fstcompile-nolex which generates different symbol tables) fst1 or fst2 can be "" (empty string) which means stdin.

* fstminimize-transducer: encode input/output, rmepsilon, determinize, minimize and decode in one pass.

* fstdeterminize-tc-lex: keep the best output for each input sequence in a transducer using determinization in the (Tropical, Categorial)-Lexicographic semiring. See "Efficient Determinization of Tagged Word Lattices using Categorial and Lexicographic Semirings", by Izhak Shafran et al, ASRU 2011.

* fstsuperfinal-noepsilon: add a superfinal state without adding epsilon arcs

* fstoracle <fst1> <fst2>: compute the shortest distance alignment between two transducers

* fstcompose-specials <fst1> <fst2>: compose two transducers using special <phi>, <rho> and <sigma> transitions. <sigma> can replace any input symbol; <rho> is like sigma but only if no other path can be followed; <phi> is an epsilon transition which can be followed if no other transition matches an input symbol. Note that lexicons from the two fsts are mapped.

fstprint sentence.fst:
0   1   the
1   2   boy
2   3   is
3   4   here
4

fstprint model.fst:
0   0   <rho> <eps>
0   1   boy XXX
1   2   is YYY
2   2   <rho> <eps>
2

./fstcompose-specials model.fst < sentence.fst | fstprint
0   1   the <eps>
1   2   boy XXX
2   3   is YYY
3   4   here <eps>
4

* fstposteriors: compute arc-level posterior probabilities from an automaton where weights are -log probs in the tropical semiring.

* fstprint-nbest-strings <n>: compute nbest and print string of input/output symbols (or input if input == output)

--- less useful / non-working stuff ---

* add-tags <dict>: generate a tagging transducer from a word acceptor according to a tab-separated, one-word-per-line tag dictionary

* ngram-expand: expand transducer so that each arc has a fixed context of up to n-1 arcs (so called ngramize) -- non functional at this time