StateMap

Description

This operation transforms each state in the input FST. The transformation is specified by a function object called a state mapper.

For instance, ArcSumMapper combines arcs with the same input label, output label and destination state, ⊕-summing their weights.

A list of available state mappers and instructions on how to create them are given here.

Usage

template <class Arc, class StateMapper> StateMap(MutableFst<Arc> *fst, StateMapper *mapper);
template <class Arc, class StateMapper> StateMap(MutableFst<Arc> *fst, StateMapper mapper);
template <class Arc, class StateMapper> StateMap(const Fst<Arc> &ifst, MutableFst<Arc> *ofst, StateMapper *mapper);
template <class Arc, class StateMapper> StateMap(const Fst<Arc> &ifst, MutableFst<Arc> *ofst, StateMapper mapper);
template <class Arc, class StateMapper> StateMapFst<Arc>:: StateMapFst(const Fst<A> &fst, StateMapper *mapper);
template <class Arc, class StateMapper> StateMapFst<Arc>:: StateMapFst(const Fst<A> &fst, const StateMapper &mapper);
fstmap [--opts] in.fst out.fst -map_type (Map operation, one of: "identity", "arc_sum") type: string default: "identity" -weight (Weight parameter) type: string default: ""

Note fstmap also includes arc mappers.

Example

A:

(TropicalWeight)

StateMap(&A, ArcSumMapper(A)):

StateMap(&A, ArcSumMapper<StdArc>(A));
StateMap(A, &B, ArcSumMapper<StdArc>(A));
StateMapFst B(A, ArcSumMapper<StdArc>(A));

fstmap --map_type=arc_sum a.fst b.fst

Complexity

StateMap:

• Time: O(c*V)
• Space: O(m)

where V = # of states, c = cost of processing one state by the mapper and m = total memory usage for the mapper.

StateMapFst:

• Time: O(c*v)
• Space: O(m)

where v = # of visited states, c = cost of processing one state by the mapper and m = total memory usage for the mapper. Constant time and space to visit an input state is assumed and exclusive of caching.

For instance in the case of ArcSumMap, we have c = O(D log(D)) and m = O(D), where D = maximum out-degree.

See Also

ArcMap, State Mappers