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
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
|
// $Id$
/***********************************************************************
Moses - factored phrase-based language decoder
Copyright (C) 2006 University of Edinburgh
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
***********************************************************************/
#include <algorithm>
#include <set>
#include <queue>
#include "HypothesisStack.h"
#include "TypeDef.h"
#include "Util.h"
#include "StaticData.h"
using namespace std;
HypothesisStack::HypothesisStack()
{
m_nBestIsEnabled = StaticData::Instance().IsNBestEnabled();
m_bestScore = -std::numeric_limits<float>::infinity();
m_worstScore = -std::numeric_limits<float>::infinity();
}
/** remove all hypotheses from the collection */
void HypothesisStack::RemoveAll()
{
while (m_hypos.begin() != m_hypos.end())
{
Remove(m_hypos.begin());
}
}
pair<HypothesisStack::iterator, bool> HypothesisStack::Add(Hypothesis *hypo)
{
std::pair<iterator, bool> ret = m_hypos.insert(hypo);
if (ret.second)
{ // equiv hypo doesn't exists
VERBOSE(3,"added hyp to stack");
// Update best score, if this hypothesis is new best
if (hypo->GetTotalScore() > m_bestScore)
{
VERBOSE(3,", best on stack");
m_bestScore = hypo->GetTotalScore();
// this may also affect the worst score
if ( m_bestScore + m_beamWidth > m_worstScore )
m_worstScore = m_bestScore + m_beamWidth;
}
// Prune only if stack is twice as big as needed (lazy pruning)
VERBOSE(3,", now size " << m_hypos.size());
if (m_hypos.size() > 2*m_maxHypoStackSize-1)
{
PruneToSize(m_maxHypoStackSize);
}
else {
VERBOSE(3,std::endl);
}
}
return ret;
}
void HypothesisStack::AddPrune(Hypothesis *hypo)
{
if (hypo->GetTotalScore() < m_worstScore)
{ // really bad score. don't bother adding hypo into collection
StaticData::Instance().GetSentenceStats().AddDiscarded();
VERBOSE(3,"discarded, too bad for stack" << std::endl);
FREEHYPO(hypo);
return;
}
// over threshold, try to add to collection
std::pair<iterator, bool> addRet = Add(hypo);
if (addRet.second)
{ // nothing found. add to collection
return;
}
// equiv hypo exists, recombine with other hypo
iterator &iterExisting = addRet.first;
Hypothesis *hypoExisting = *iterExisting;
assert(iterExisting != m_hypos.end());
StaticData::Instance().GetSentenceStats().AddRecombination(*hypo, **iterExisting);
// found existing hypo with same target ending.
// keep the best 1
if (hypo->GetTotalScore() > hypoExisting->GetTotalScore())
{ // incoming hypo is better than the one we have
VERBOSE(3,"better than matching hyp " << hypoExisting->GetId() << ", recombining, ");
if (m_nBestIsEnabled) {
hypo->AddArc(hypoExisting);
Detach(iterExisting);
} else {
Remove(iterExisting);
}
bool added = Add(hypo).second;
if (!added)
{
iterExisting = m_hypos.find(hypo);
TRACE_ERR("Offending hypo = " << **iterExisting << endl);
abort();
}
return;
}
else
{ // already storing the best hypo. discard current hypo
VERBOSE(3,"worse than matching hyp " << hypoExisting->GetId() << ", recombining" << std::endl)
if (m_nBestIsEnabled) {
hypoExisting->AddArc(hypo);
} else {
FREEHYPO(hypo);
}
return;
}
}
void HypothesisStack::PruneToSize(size_t newSize)
{
if (m_hypos.size() > newSize) // ok, if not over the limit
{
priority_queue<float> bestScores;
// push all scores to a heap
// (but never push scores below m_bestScore+m_beamWidth)
iterator iter = m_hypos.begin();
float score = 0;
while (iter != m_hypos.end())
{
Hypothesis *hypo = *iter;
score = hypo->GetTotalScore();
if (score > m_bestScore+m_beamWidth)
{
bestScores.push(score);
}
++iter;
}
// pop the top newSize scores (and ignore them, these are the scores of hyps that will remain)
// ensure to never pop beyond heap size
size_t minNewSizeHeapSize = newSize > bestScores.size() ? bestScores.size() : newSize;
for (size_t i = 1 ; i < minNewSizeHeapSize ; i++)
bestScores.pop();
// and remember the threshold
float scoreThreshold = bestScores.top();
// delete all hypos under score threshold
iter = m_hypos.begin();
while (iter != m_hypos.end())
{
Hypothesis *hypo = *iter;
float score = hypo->GetTotalScore();
if (score < scoreThreshold)
{
iterator iterRemove = iter++;
Remove(iterRemove);
StaticData::Instance().GetSentenceStats().AddPruning();
}
else
{
++iter;
}
}
VERBOSE(3,", pruned to size " << size() << endl);
IFVERBOSE(3)
{
TRACE_ERR("stack now contains: ");
for(iter = m_hypos.begin(); iter != m_hypos.end(); iter++)
{
Hypothesis *hypo = *iter;
TRACE_ERR( hypo->GetId() << " (" << hypo->GetTotalScore() << ") ");
}
TRACE_ERR( endl);
}
// set the worstScore, so that newly generated hypotheses will not be added if worse than the worst in the stack
m_worstScore = scoreThreshold;
}
}
const Hypothesis *HypothesisStack::GetBestHypothesis() const
{
if (!m_hypos.empty())
{
const_iterator iter = m_hypos.begin();
Hypothesis *bestHypo = *iter;
while (++iter != m_hypos.end())
{
Hypothesis *hypo = *iter;
if (hypo->GetTotalScore() > bestHypo->GetTotalScore())
bestHypo = hypo;
}
return bestHypo;
}
return NULL;
}
vector<const Hypothesis*> HypothesisStack::GetSortedList() const
{
vector<const Hypothesis*> ret; ret.reserve(m_hypos.size());
std::copy(m_hypos.begin(), m_hypos.end(), std::inserter(ret, ret.end()));
sort(ret.begin(), ret.end(), CompareHypothesisTotalScore());
return ret;
}
void HypothesisStack::CleanupArcList()
{
// only necessary if n-best calculations are enabled
if (!m_nBestIsEnabled) return;
iterator iter;
for (iter = m_hypos.begin() ; iter != m_hypos.end() ; ++iter)
{
Hypothesis *mainHypo = *iter;
mainHypo->CleanupArcList();
}
}
TO_STRING_BODY(HypothesisStack);
// friend
std::ostream& operator<<(std::ostream& out, const HypothesisStack& hypoColl)
{
HypothesisStack::const_iterator iter;
for (iter = hypoColl.begin() ; iter != hypoColl.end() ; ++iter)
{
const Hypothesis &hypo = **iter;
out << hypo << endl;
}
return out;
}
|