1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
|
// push.h
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Copyright 2005-2010 Google, Inc.
// Author: allauzen@google.com (Cyril Allauzen)
//
// \file
// Class to reweight/push an FST.
#ifndef FST_LIB_PUSH_H__
#define FST_LIB_PUSH_H__
#include <vector>
using std::vector;
#include <fst/factor-weight.h>
#include <fst/fst.h>
#include <fst/arc-map.h>
#include <fst/reweight.h>
#include <fst/shortest-distance.h>
namespace fst {
// Private helper functions for Push
namespace internal {
// Compute the total weight (sum of the weights of all accepting paths) from
// the output of ShortestDistance. 'distance' is the shortest distance from the
// initial state when 'reverse == false' and to the final states when
// 'reverse == true'.
template <class Arc>
typename Arc::Weight ComputeTotalWeight(
const Fst<Arc> &fst,
const vector<typename Arc::Weight> &distance,
bool reverse) {
if (reverse)
return fst.Start() < distance.size() ?
distance[fst.Start()] : Arc::Weight::Zero();
typename Arc::Weight sum = Arc::Weight::Zero();
for (typename Arc::StateId s = 0; s < distance.size(); ++s)
sum = Plus(sum, Times(distance[s], fst.Final(s)));
return sum;
}
// Divide the weight of every accepting path by 'w'. The weight 'w' is
// divided at the final states if 'at_final == true' and at the
// initial state otherwise.
template <class Arc>
void RemoveWeight(MutableFst<Arc> *fst, typename Arc::Weight w, bool at_final) {
if ((w == Arc::Weight::One()) || (w == Arc::Weight::Zero()))
return;
if (at_final) {
// Remove 'w' from the final states
for (StateIterator< MutableFst<Arc> > sit(*fst);
!sit.Done();
sit.Next())
fst->SetFinal(sit.Value(),
Divide(fst->Final(sit.Value()), w, DIVIDE_RIGHT));
} else { // at_final == false
// Remove 'w' from the initial state
typename Arc::StateId start = fst->Start();
for (MutableArcIterator<MutableFst<Arc> > ait(fst, start);
!ait.Done();
ait.Next()) {
Arc arc = ait.Value();
arc.weight = Divide(arc.weight, w, DIVIDE_LEFT);
ait.SetValue(arc);
}
fst->SetFinal(start, Divide(fst->Final(start), w, DIVIDE_LEFT));
}
}
} // namespace internal
// Pushes the weights in FST in the direction defined by TYPE. If
// pushing towards the initial state, the sum of the weight of the
// outgoing transitions and final weight at a non-initial state is
// equal to One() in the resulting machine. If pushing towards the
// final state, the same property holds on the reverse machine.
//
// Weight needs to be left distributive when pushing towards the
// initial state and right distributive when pushing towards the final
// states.
template <class Arc>
void Push(MutableFst<Arc> *fst,
ReweightType type,
float delta = kDelta,
bool remove_total_weight = false) {
vector<typename Arc::Weight> distance;
ShortestDistance(*fst, &distance, type == REWEIGHT_TO_INITIAL, delta);
typename Arc::Weight total_weight = Arc::Weight::One();
if (remove_total_weight)
total_weight = internal::ComputeTotalWeight(*fst, distance,
type == REWEIGHT_TO_INITIAL);
Reweight(fst, distance, type);
if (remove_total_weight)
internal::RemoveWeight(fst, total_weight, type == REWEIGHT_TO_FINAL);
}
const uint32 kPushWeights = 0x0001;
const uint32 kPushLabels = 0x0002;
const uint32 kPushRemoveTotalWeight = 0x0004;
const uint32 kPushRemoveCommonAffix = 0x0008;
// OFST obtained from IFST by pushing weights and/or labels according
// to PTYPE in the direction defined by RTYPE. Weight needs to be
// left distributive when pushing weights towards the initial state
// and right distributive when pushing weights towards the final
// states.
template <class Arc, ReweightType rtype>
void Push(const Fst<Arc> &ifst,
MutableFst<Arc> *ofst,
uint32 ptype,
float delta = kDelta) {
if ((ptype & (kPushWeights | kPushLabels)) == kPushWeights) {
*ofst = ifst;
Push(ofst, rtype, delta, ptype & kPushRemoveTotalWeight);
} else if (ptype & kPushLabels) {
const StringType stype = rtype == REWEIGHT_TO_INITIAL
? STRING_LEFT
: STRING_RIGHT;
vector<typename GallicArc<Arc, stype>::Weight> gdistance;
VectorFst<GallicArc<Arc, stype> > gfst;
ArcMap(ifst, &gfst, ToGallicMapper<Arc, stype>());
if (ptype & kPushWeights ) {
ShortestDistance(gfst, &gdistance, rtype == REWEIGHT_TO_INITIAL, delta);
} else {
ArcMapFst<Arc, Arc, RmWeightMapper<Arc> >
uwfst(ifst, RmWeightMapper<Arc>());
ArcMapFst<Arc, GallicArc<Arc, stype>, ToGallicMapper<Arc, stype> >
guwfst(uwfst, ToGallicMapper<Arc, stype>());
ShortestDistance(guwfst, &gdistance, rtype == REWEIGHT_TO_INITIAL, delta);
}
typename GallicArc<Arc, stype>::Weight total_weight =
GallicArc<Arc, stype>::Weight::One();
if (ptype & (kPushRemoveTotalWeight | kPushRemoveCommonAffix)) {
total_weight = internal::ComputeTotalWeight(
gfst, gdistance, rtype == REWEIGHT_TO_INITIAL);
total_weight = typename GallicArc<Arc, stype>::Weight(
ptype & kPushRemoveCommonAffix ? total_weight.Value1()
: StringWeight<typename Arc::Label, stype>::One(),
ptype & kPushRemoveTotalWeight ? total_weight.Value2()
: Arc::Weight::One());
}
Reweight(&gfst, gdistance, rtype);
if (ptype & (kPushRemoveTotalWeight | kPushRemoveCommonAffix))
internal::RemoveWeight(&gfst, total_weight, rtype == REWEIGHT_TO_FINAL);
FactorWeightFst< GallicArc<Arc, stype>, GallicFactor<typename Arc::Label,
typename Arc::Weight, stype> > fwfst(gfst);
ArcMap(fwfst, ofst, FromGallicMapper<Arc, stype>());
ofst->SetOutputSymbols(ifst.OutputSymbols());
} else {
LOG(WARNING) << "Push: pushing type is set to 0: "
<< "pushing neither labels nor weights.";
*ofst = ifst;
}
}
} // namespace fst
#endif /* FST_LIB_PUSH_H_ */
|
