partialtransloptcoll.cpp.svn-base

moses开源的机器翻译系统

// $Id$

/***********************************************************************
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 "PartialTranslOptColl.h"
#include <algorithm>

/** constructor, intializes counters and thresholds */
PartialTranslOptColl::PartialTranslOptColl()
{
	m_bestScore = -std::numeric_limits<float>::infinity();
	m_worstScore = -std::numeric_limits<float>::infinity();
	m_maxSize = StaticData::Instance().GetMaxNoPartTransOpt();
	m_totalPruned = 0;
}


/** add a partial translation option to the collection (without pruning) */
void PartialTranslOptColl::AddNoPrune(TranslationOption *partialTranslOpt)
{
	partialTranslOpt->CalcScore();
	if (partialTranslOpt->GetFutureScore() >= m_worstScore) 
	{
		m_list.push_back(partialTranslOpt);
		if (partialTranslOpt->GetFutureScore() > m_bestScore)
			m_bestScore = partialTranslOpt->GetFutureScore();
	}		
	else
	{
		m_totalPruned++;
		delete partialTranslOpt;
	}
}

/** add a partial translation option to the collection, prune if necessary.
 * This is done similar to the Prune() in TranslationOptionCollection */ 

void PartialTranslOptColl::Add(TranslationOption *partialTranslOpt)
{
	// add
	AddNoPrune( partialTranslOpt );
	
	// done if not too large (lazy pruning, only if twice as large as max)
	if ( m_list.size() > 2 * m_maxSize ) {
		Prune();
	}
}


/** helper, used by pruning */
bool ComparePartialTranslationOption(const TranslationOption *a, const TranslationOption *b)
{
	return a->GetFutureScore() > b->GetFutureScore();
}

/** pruning, remove partial translation options, if list too big */
void PartialTranslOptColl::Prune()
{
	// done if not too big
	if ( m_list.size() <= m_maxSize ) {
		return;
	}
	
	//	TRACE_ERR( "pruning partial translation options from size " << m_list.size() << std::endl);
	
	// find nth element
	nth_element(m_list.begin(), 
							m_list.begin() + m_maxSize, 
							m_list.end(), 
							ComparePartialTranslationOption);
	
	m_worstScore = m_list[ m_maxSize-1 ]->GetFutureScore();
	// delete the rest
	for (size_t i = m_maxSize ; i < m_list.size() ; ++i)
	{
		delete m_list[i];
		m_totalPruned++;
	}
	m_list.resize(m_maxSize);
	//	TRACE_ERR( "pruned to size " << m_list.size() << ", total pruned: " << m_totalPruned << std::endl);
}