mirror of
https://github.com/moses-smt/mosesdecoder.git
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313 lines
12 KiB
C++
313 lines
12 KiB
C++
/***********************************************************************
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Moses - statistical machine translation system
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Copyright (C) 2006-2014 University of Edinburgh
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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This library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with this library; if not, write to the Free Software
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Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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***********************************************************************/
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#include "ChartKBestExtractor.h"
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#include "ChartHypothesis.h"
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#include "ScoreComponentCollection.h"
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#include "StaticData.h"
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#include <boost/scoped_ptr.hpp>
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#include <vector>
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using namespace std;
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namespace Moses
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{
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// Extract the k-best list from the search graph.
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void ChartKBestExtractor::Extract(
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const std::vector<const ChartHypothesis*> &topLevelHypos, std::size_t k,
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KBestVec &kBestList)
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{
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kBestList.clear();
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if (topLevelHypos.empty()) {
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return;
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}
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// Create a new ChartHypothesis object, supremeHypo, that has the best
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// top-level hypothesis as its predecessor and has the same score.
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std::vector<const ChartHypothesis*>::const_iterator p = topLevelHypos.begin();
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const ChartHypothesis &bestTopLevelHypo = **p;
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boost::scoped_ptr<ChartHypothesis> supremeHypo(
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new ChartHypothesis(bestTopLevelHypo, *this));
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// Do the same for each alternative top-level hypothesis, but add the new
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// ChartHypothesis objects as arcs from supremeHypo, as if they had been
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// recombined.
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for (++p; p != topLevelHypos.end(); ++p) {
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// Check that the first item in topLevelHypos really was the best.
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UTIL_THROW_IF2((*p)->GetTotalScore() > bestTopLevelHypo.GetTotalScore(),
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"top-level hypotheses are not correctly sorted");
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// Note: there's no need for a smart pointer here: supremeHypo will take
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// ownership of altHypo.
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ChartHypothesis *altHypo = new ChartHypothesis(**p, *this);
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supremeHypo->AddArc(altHypo);
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}
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// Create the target vertex then lazily fill its k-best list.
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boost::shared_ptr<Vertex> targetVertex = FindOrCreateVertex(*supremeHypo);
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LazyKthBest(*targetVertex, k, k);
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// Copy the k-best list from the target vertex, but drop the top edge from
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// each derivation.
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kBestList.reserve(targetVertex->kBestList.size());
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for (std::vector<boost::weak_ptr<Derivation> >::const_iterator
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q = targetVertex->kBestList.begin();
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q != targetVertex->kBestList.end(); ++q) {
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const boost::shared_ptr<Derivation> d(*q);
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assert(d);
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assert(d->subderivations.size() == 1);
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kBestList.push_back(d->subderivations[0]);
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}
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}
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// Generate the target-side yield of the derivation d.
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Phrase ChartKBestExtractor::GetOutputPhrase(const Derivation &d)
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{
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FactorType placeholderFactor = StaticData::Instance().GetPlaceholderFactor();
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Phrase ret(ARRAY_SIZE_INCR);
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const ChartHypothesis &hypo = d.edge.head->hypothesis;
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const TargetPhrase &phrase = hypo.GetCurrTargetPhrase();
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const AlignmentInfo::NonTermIndexMap &nonTermIndexMap =
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phrase.GetAlignNonTerm().GetNonTermIndexMap();
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for (std::size_t pos = 0; pos < phrase.GetSize(); ++pos) {
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const Word &word = phrase.GetWord(pos);
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if (word.IsNonTerminal()) {
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std::size_t nonTermInd = nonTermIndexMap[pos];
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const Derivation &subderivation = *d.subderivations[nonTermInd];
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Phrase subPhrase = GetOutputPhrase(subderivation);
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ret.Append(subPhrase);
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} else {
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ret.AddWord(word);
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if (placeholderFactor == NOT_FOUND) {
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continue;
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}
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std::set<std::size_t> sourcePosSet =
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phrase.GetAlignTerm().GetAlignmentsForTarget(pos);
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if (sourcePosSet.size() == 1) {
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const std::vector<const Word*> *ruleSourceFromInputPath =
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hypo.GetTranslationOption().GetSourceRuleFromInputPath();
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UTIL_THROW_IF2(ruleSourceFromInputPath == NULL,
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"Source Words in of the rules hasn't been filled out");
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std::size_t sourcePos = *sourcePosSet.begin();
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const Word *sourceWord = ruleSourceFromInputPath->at(sourcePos);
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UTIL_THROW_IF2(sourceWord == NULL,
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"Null source word at position " << sourcePos);
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const Factor *factor = sourceWord->GetFactor(placeholderFactor);
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if (factor) {
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ret.Back()[0] = factor;
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}
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}
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}
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}
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return ret;
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}
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// Generate the target tree of the derivation d.
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TreePointer ChartKBestExtractor::GetOutputTree(const Derivation &d)
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{
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const ChartHypothesis &hypo = d.edge.head->hypothesis;
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const TargetPhrase &phrase = hypo.GetCurrTargetPhrase();
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if (const PhraseProperty *property = phrase.GetProperty("Tree")) {
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const std::string *tree = property->GetValueString();
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TreePointer mytree (boost::make_shared<InternalTree>(*tree));
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//get subtrees (in target order)
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std::vector<TreePointer> previous_trees;
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for (size_t pos = 0; pos < phrase.GetSize(); ++pos) {
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const Word &word = phrase.GetWord(pos);
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if (word.IsNonTerminal()) {
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size_t nonTermInd = phrase.GetAlignNonTerm().GetNonTermIndexMap()[pos];
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const Derivation &subderivation = *d.subderivations[nonTermInd];
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const TreePointer prev_tree = GetOutputTree(subderivation);
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previous_trees.push_back(prev_tree);
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}
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}
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mytree->Combine(previous_trees);
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return mytree;
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}
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else {
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UTIL_THROW2("Error: TreeStructureFeature active, but no internal tree structure found");
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}
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}
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// Create an unweighted hyperarc corresponding to the given ChartHypothesis.
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ChartKBestExtractor::UnweightedHyperarc ChartKBestExtractor::CreateEdge(
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const ChartHypothesis &h)
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{
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UnweightedHyperarc edge;
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edge.head = FindOrCreateVertex(h);
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const std::vector<const ChartHypothesis*> &prevHypos = h.GetPrevHypos();
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edge.tail.resize(prevHypos.size());
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for (std::size_t i = 0; i < prevHypos.size(); ++i) {
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const ChartHypothesis *prevHypo = prevHypos[i];
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edge.tail[i] = FindOrCreateVertex(*prevHypo);
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}
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return edge;
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}
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// Look for the vertex corresponding to a given ChartHypothesis, creating
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// a new one if necessary.
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boost::shared_ptr<ChartKBestExtractor::Vertex>
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ChartKBestExtractor::FindOrCreateVertex(const ChartHypothesis &h)
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{
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VertexMap::value_type element(&h, boost::shared_ptr<Vertex>());
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std::pair<VertexMap::iterator, bool> p = m_vertexMap.insert(element);
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boost::shared_ptr<Vertex> &sp = p.first->second;
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if (!p.second) {
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return sp; // Vertex was already in m_vertexMap.
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}
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sp.reset(new Vertex(h));
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// Create the 1-best derivation and add it to the vertex's kBestList.
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UnweightedHyperarc bestEdge;
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bestEdge.head = sp;
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const std::vector<const ChartHypothesis*> &prevHypos = h.GetPrevHypos();
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bestEdge.tail.resize(prevHypos.size());
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for (std::size_t i = 0; i < prevHypos.size(); ++i) {
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const ChartHypothesis *prevHypo = prevHypos[i];
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bestEdge.tail[i] = FindOrCreateVertex(*prevHypo);
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}
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boost::shared_ptr<Derivation> bestDerivation(new Derivation(bestEdge));
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#ifndef NDEBUG
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std::pair<DerivationSet::iterator, bool> q =
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#endif
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m_derivations.insert(bestDerivation);
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assert(q.second);
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sp->kBestList.push_back(bestDerivation);
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return sp;
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}
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// Create the 1-best derivation for each edge in BS(v) (except the best one)
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// and add it to v's candidate queue.
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void ChartKBestExtractor::GetCandidates(Vertex &v, std::size_t k)
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{
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// Create derivations for all of v's incoming edges except the best. This
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// means everything in v.hypothesis.GetArcList() and not the edge defined
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// by v.hypothesis itself. The 1-best derivation for that edge will already
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// have been created.
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const ChartArcList *arcList = v.hypothesis.GetArcList();
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if (arcList) {
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for (std::size_t i = 0; i < arcList->size(); ++i) {
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const ChartHypothesis &recombinedHypo = *(*arcList)[i];
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boost::shared_ptr<Vertex> w = FindOrCreateVertex(recombinedHypo);
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assert(w->kBestList.size() == 1);
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v.candidates.push(w->kBestList[0]);
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}
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}
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}
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// Lazily fill v's k-best list.
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void ChartKBestExtractor::LazyKthBest(Vertex &v, std::size_t k,
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std::size_t globalK)
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{
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// If this is the first visit to vertex v then initialize the priority queue.
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if (v.visited == false) {
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// The 1-best derivation should already be in v's k-best list.
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assert(v.kBestList.size() == 1);
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// Initialize v's priority queue.
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GetCandidates(v, globalK);
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v.visited = true;
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}
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// Add derivations to the k-best list until it contains k or there are none
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// left to add.
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while (v.kBestList.size() < k) {
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assert(!v.kBestList.empty());
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// Update the priority queue by adding the successors of the last
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// derivation (unless they've been seen before).
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boost::shared_ptr<Derivation> d(v.kBestList.back());
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LazyNext(v, *d, globalK);
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// Check if there are any derivations left in the queue.
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if (v.candidates.empty()) {
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break;
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}
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// Get the next best derivation and delete it from the queue.
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boost::weak_ptr<Derivation> next = v.candidates.top();
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v.candidates.pop();
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// Add it to the k-best list.
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v.kBestList.push_back(next);
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}
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}
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// Create the neighbours of Derivation d and add them to v's candidate queue.
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void ChartKBestExtractor::LazyNext(Vertex &v, const Derivation &d,
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std::size_t globalK)
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{
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for (std::size_t i = 0; i < d.edge.tail.size(); ++i) {
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Vertex &pred = *d.edge.tail[i];
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// Ensure that pred's k-best list contains enough derivations.
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std::size_t k = d.backPointers[i] + 2;
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LazyKthBest(pred, k, globalK);
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if (pred.kBestList.size() < k) {
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// pred's derivations have been exhausted.
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continue;
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}
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// Create the neighbour.
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boost::shared_ptr<Derivation> next(new Derivation(d, i));
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// Check if it has been created before.
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std::pair<DerivationSet::iterator, bool> p = m_derivations.insert(next);
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if (p.second) {
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v.candidates.push(next); // Haven't previously seen it.
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}
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}
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}
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// Construct the 1-best Derivation that ends at edge e.
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ChartKBestExtractor::Derivation::Derivation(const UnweightedHyperarc &e)
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{
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edge = e;
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std::size_t arity = edge.tail.size();
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backPointers.resize(arity, 0);
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subderivations.reserve(arity);
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for (std::size_t i = 0; i < arity; ++i) {
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const Vertex &pred = *edge.tail[i];
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assert(pred.kBestList.size() >= 1);
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boost::shared_ptr<Derivation> sub(pred.kBestList[0]);
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subderivations.push_back(sub);
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}
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scoreBreakdown = edge.head->hypothesis.GetScoreBreakdown();
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score = edge.head->hypothesis.GetTotalScore();
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}
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// Construct a Derivation that neighbours an existing Derivation.
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ChartKBestExtractor::Derivation::Derivation(const Derivation &d, std::size_t i)
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{
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edge.head = d.edge.head;
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edge.tail = d.edge.tail;
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backPointers = d.backPointers;
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subderivations = d.subderivations;
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std::size_t j = ++backPointers[i];
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scoreBreakdown = d.scoreBreakdown;
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// Deduct the score of the old subderivation.
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scoreBreakdown.MinusEquals(subderivations[i]->scoreBreakdown);
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// Update the subderivation pointer.
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boost::shared_ptr<Derivation> newSub(edge.tail[i]->kBestList[j]);
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subderivations[i] = newSub;
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// Add the score of the new subderivation.
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scoreBreakdown.PlusEquals(subderivations[i]->scoreBreakdown);
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score = scoreBreakdown.GetWeightedScore();
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}
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} // namespace Moses
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