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Determinize

Description

This operation determinizes a weighted transducer. The result will be an equivalent FST that has the property that no state has two transitions with the same input label. For this algorithm, epsilon transitions are treated as regular symbols (cf. RmEpsilon).

The transducer must be functional. The weights must be (weakly) left divisible (valid for TropicalWeight and LogWeight for instance) and zero-sum-free.

Usage

template <class Arc>
void Determinize(const Fst<Arc> &ifst, MutableFst<Arc> *ofst);
%DOX{namespacefst.html#Determinize[doc]}%
template <class Arc> DeterminizeFst<Arc>::
DeterminizeFst(const Fst<Arc> &fst);
%DOX{fst::DeterminizeFst[doc]}%
fstdeterminize a.fst out.fst
 

Examples

A:

determinize1.jpg

(TropicalWeight)

Determinize of A:

determinize2.jpg

Determinize(&A);
DeterminizeFst<Arc>(A);
fstdeterminize a.fst out.fst

Complexity

Determinize:
  • Determinizable: exponential (polynomial in the size of the output)
  • Non-determinizable: does not terminate
DeterminizeFst:
  • Determinizable: exponential (polynomial in the size of the output)
  • Non-determinizable: does not terminate

The determinizable automata include all unweighted and all acyclic input.

Caveats

Epsilons may be added as input labels at the ends of paths when determinizing transducers. If input transducer also contains epsilons, this may result in a non-deterministic result even when the epsilons are treated as regular symbols. The subsequential label can be chosen as a non-zero value to avoid this issue by passing it as an option (in a variant call to this function/class).

Non-functional transducers can be handled by passing the 'disambiguate_output' option when the semiring has the path property (in a variant call to this function/class). In this case, only the shortest path output for each input is retained.

See Also

Disambiguate, RmEpsilon

References

-- MichaelRiley - 20 Jun 2007

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JPEGjpg determinize1.jpg r2 r1 manage 12.5 K 2007-06-21 - 21:43 MichaelRiley  
JPEGjpg determinize2.jpg r2 r1 manage 13.7 K 2007-06-21 - 21:43 MichaelRiley  
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Topic revision: r13 - 2014-05-06 - MichaelRiley
 
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