MertPrune.cpp

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//Copyright (c) 2012, University of Cambridge
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#include "MertPrune.h"

PruneStats::PruneStats() :
  before (0), after (0) {
}
;

void Prune (fst::MutableFst<FunctionArc> *fst, PruneStats& stats) {
  stats.before += ArcCount (*fst);
  Prune (fst);
  stats.after += ArcCount (*fst);
}

void FullPrune (fst::MutableFst<FunctionArc> *fst,
                const std::vector<FunctionWeight>& distance, PruneStats& stats) {
  stats.before += ArcCount (*fst);
  FullPrune (fst, distance);
  stats.after += ArcCount (*fst);
}

void Prune (fst::MutableFst<FunctionArc> *fst) {
  std::map<StatePair, int> dupeArcs;
  std::map<StatePair, FunctionWeight> summedWeights;
  int totalArcs = 0;
  for (fst::StateIterator < fst::MutableFst<FunctionArc> > siter (*fst);
       !siter.Done(); siter.Next() ) {
    FunctionArc::StateId startState = siter.Value();
    int arcCount = 0;
    for (fst::ArcIterator < fst::MutableFst<FunctionArc> > aiter (*fst,
         siter.Value() ); !aiter.Done(); aiter.Next() ) {
      ++totalArcs;
      ++arcCount;
      const FunctionArc& arc = aiter.Value();
      FunctionArc::StateId endState = arc.nextstate;
      StatePair pair (startState, endState);
      if (summedWeights.count (pair) == 0) {
        summedWeights[pair] = arc.weight;
        dupeArcs[pair] = 1;
      } else {
        summedWeights[pair] = Plus (summedWeights[pair], arc.weight);
        dupeArcs[pair] += 1;
      }
    }
    //cout << startState << "\t" << arcCount << endl;
  }
  FunctionArc::StateId deadState = fst->AddState();
  for (std::map<StatePair, int>::iterator it = dupeArcs.begin(); it
       != dupeArcs.end(); ++it) {
    if (it->second > 1) {
      for (fst::MutableArcIterator < fst::MutableFst<FunctionArc> > aiter (fst,
           it->first.first); !aiter.Done(); aiter.Next() ) {
        FunctionArc arc = aiter.Value();
        bool keepArc = false;
        if (arc.nextstate == it->first.second) {
          for (MertList::const_iterator miter =
                 summedWeights[it->first].Value().begin(); miter
               != summedWeights[it->first].Value().end(); ++miter) {
            keepArc |= arc.weight.Value().front() == *miter;
          }
          if (!keepArc) {
            arc.nextstate = deadState;
            aiter.SetValue (arc);
          }
        }
      }
    }
    //cout << it->first.first << "->" << it->first.second << "\t"
    //    << it->second << endl;
  }
  Connect (fst);
}

void FullPrune (fst::MutableFst<FunctionArc> *fst,
                const std::vector<FunctionWeight>& distance) {
  FunctionArc::StateId deadState = fst->AddState();
  for (fst::StateIterator < fst::MutableFst<FunctionArc> > siter (*fst);
       !siter.Done(); siter.Next() ) {
    std::map<FunctionArc::StateId, FunctionWeight> otherArcs;
    for (fst::ArcIterator < fst::Fst<FunctionArc> > aiter (*fst, siter.Value() );
         !aiter.Done(); aiter.Next() ) {
      FunctionArc arc = aiter.Value();
      if (otherArcs.count (arc.nextstate) == 0) {
        otherArcs[arc.nextstate] = Times (arc.weight, distance[arc.nextstate]);
      } else {
        otherArcs[arc.nextstate] = Plus (otherArcs[arc.nextstate],
                                         Times (arc.weight, distance[arc.nextstate]) );
      }
    }
    /*for (map<FunctionArc::StateId, FunctionWeight>::iterator miter =
        otherArcs.begin(); miter != otherArcs.end(); ++miter) {
      miter->second = Times(miter->second, distance[miter->first]);
    }*/
    std::set<FunctionArc::StateId> toDelete;
    for (std::map<FunctionArc::StateId, FunctionWeight>::iterator outer =
           otherArcs.begin(); outer != otherArcs.end(); ++outer) {
      FunctionWeight otherSum = FunctionWeight::Zero();
      for (std::map<FunctionArc::StateId, FunctionWeight>::iterator inner =
             otherArcs.begin(); inner != otherArcs.end(); ++inner) {
        if (outer->first != inner->first) {
          otherSum = Plus (otherSum, inner->second);
        }
      }
      if (otherSum == distance[siter.Value()]) {
        toDelete.insert (outer->first);
      }
    }
    for (fst::MutableArcIterator < fst::MutableFst<FunctionArc> > aiter (fst,
         siter.Value() ); !aiter.Done(); aiter.Next() ) {
      FunctionArc arc = aiter.Value();
      if (toDelete.count (arc.nextstate) > 0) {
        arc.nextstate = deadState;
        aiter.SetValue (arc);
      }
    }
  }
  Connect (fst);
}

int ArcCount (const fst::Fst<FunctionArc>& fst) {
  int arcs = 0;
  for (fst::StateIterator < fst::Fst<FunctionArc> > siter (fst); !siter.Done();
       siter.Next() ) {
    FunctionArc::StateId startState = siter.Value();
    for (fst::ArcIterator < fst::Fst<FunctionArc> > aiter (fst, siter.Value() );
         !aiter.Done(); aiter.Next() ) {
      ++arcs;
    }
    //cout << startState << "\t" << arcCount << endl;
  }
  return arcs;
}