FstPathFinder.cpp

/*
 FstPathFinder.cpp

 Copyright (c) [2012-], Josef Robert Novak
 All rights reserved.

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  are met:

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  notice, this list of conditions and the following disclaimer.
  * Redistributions in binary form must reproduce the above 
  copyright notice, this list of #conditions and the following 
    disclaimer in the documentation and/or other materials provided 
    with the distribution.

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  "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 
  LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 
 FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 
  COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, 
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#include "FstPathFinder.hpp"

FstPathFinder::FstPathFinder( ){
  //By default we'll just skip <eps>
  skip.insert(0);
  band = 999999;
}

FstPathFinder::FstPathFinder( set<int> _skip, unsigned int _band ){
  skip  = _skip;
  band  = _band;
}

void FstPathFinder::extract_all_paths( const VectorFst<StdArc>& ifst ){
  vector<int> path;
  //Extract the paths
  _extract_paths( ifst, ifst.Start(), path, LogWeight::One() );
  //Now resort them in case the order has changed
  ////This actually seems to make the results WORSE not better
  ////Maybe because we aren't normalizing the lattice?
  //// CHECK IT LATER
  ////sort(paths.begin(), paths.end(), pathdata_pred());
  return;
}

void FstPathFinder::_extract_paths( const VectorFst<StdArc>& ifst, StdArc::StateId id, vector<int>& path, LogWeight cost ){

  if( ifst.Final(id) != TropicalWeight::Zero() ){
    cost = Times(cost, ifst.Final(id).Value());
    //We will almost always have unique nbest<10 so this is actually pretty efficient
    bool equals = false;
    for( unsigned int i=0; i<paths.size(); i++ ){
      //If the path is redundant, sum the probability mass
      if( equal( path.begin(), path.end(), paths[i].path.begin() ) ){
	////This actually seems to make the results WORSE not better
	////Maybe because we aren't normalizing the lattice?
	//// CHECK IT LATER
	////paths[i].cost = Plus(paths[i].cost, cost);
	equals = true;
      }
    }

    //If this is a new path, add it to the vector
    if( equals==false )
      paths.push_back( PathData(path, cost) );
    //Now clear the path and terminate the recursion
    path.clear();
    return;
  }


  for( ArcIterator<VectorFst<StdArc> > aiter(ifst,id); !aiter.Done(); aiter.Next() ) {
    const StdArc& arc = aiter.Value();
    if( skip.count(arc.ilabel)==0 )
      path.push_back(arc.ilabel);
    if( paths.size()<=band )
      _extract_paths( ifst, arc.nextstate, path, Times(cost, arc.weight.Value()) );
  }

}