src/WeakLearners/BaseLearner.cpp

/*
* This file is part of MultiBoost, a multi-class 
* AdaBoost learner/classifier
*
* Copyright (C) 2005 Norman Casagrande
* For informations write to nova77@gmail.com
*
* 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 St, Fifth Floor, Boston, MA  02110-1301  USA
*
*/

#include <cmath> // for log

#include "WeakLearners/BaseLearner.h"
#include "Utils/Utils.h" // for is_zero
#include "IO/Serialization.h" // for the helper function "standardTag"

namespace MultiBoost {

// -----------------------------------------------------------------------

InputData* BaseLearner::createInputData()
{
   return new InputData();
}

// -----------------------------------------------------------------------

double BaseLearner::getAlpha(const double error)
{
   return 0.5 * log( (1-error)/error );
}

// -----------------------------------------------------------------------

double BaseLearner::getAlpha(const double eps_min, const double eps_pls)
{
   return 0.5 * log( (eps_pls + _smoothingVal) / (eps_min + _smoothingVal) );
}

// -----------------------------------------------------------------------

double BaseLearner::getAlpha(const double eps_min, const double eps_pls, 
                             const double theta)
{
   // if theta == 0
   if ( nor_utils::is_zero(theta) )
      return getAlpha( eps_min, eps_pls );

   const double eps_zero = 1 - eps_min - eps_pls;

   if (eps_min < _smallVal)
   {
      // if eps_min == 0
      return log( ( (1-theta)* eps_pls ) / (theta * eps_zero) );
   }
   else
   {
      // ln( -b + sqrt( b^2 + c) );
      const double denom = (1+theta) * eps_min;
      const double b = ((theta) * eps_zero) / (2*denom);
      const double c = ((1-theta) * eps_pls) / denom;

      return log( -b + sqrt( b * b + c ) );
   }

}

// -----------------------------------------------------------------------

void BaseLearner::save(ofstream& outputStream, const int numTabs)
{
   // save alpha
   outputStream << Serialization::standardTag("alpha", _alpha, numTabs) << endl;
}

// -----------------------------------------------------------------------

void BaseLearner::load(nor_utils::StreamTokenizer& st)
{
   _alpha = UnSerialization::seekAndParseEnclosedValue<double>(st, "alpha");
}

// -----------------------------------------------------------------------

} // end of namespace MultiBoost

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