baselearner.cpp

MultiBoost 是c++实现的多类adaboost酸法。与传统的adaboost算法主要解决二类分类问题不同

/*
* This file is part of MultiBoost, a multi-class 
* AdaBoost learner/classifier
*
* Copyright (C) 2005-2006 Norman Casagrande
* For informations write to [e-mail]
*
* 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 {

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

void BaseLearner::declareBaseArguments(nor_utils::Args& args)
{
   args.setGroup("I/O Options");

   args.declareArgument("d", "The separation characters between the fields (default: whitespaces).\nExample: -d \"\\t,.-\"\nNote: new-line is always included!", 1, "<separators>");
   args.declareArgument("classend", "The class is the last column instead of the first (or second if -examplelabel is active).");
   args.declareArgument("classmap", "Specify a file with the list of classes. Use it when the test set has less classes than the training set.", 1, "<filename>");
   args.declareArgument("examplelabel", "The data file has an additional column (the very first) which contains the label of the example.");
   args.declareArgument("shypname", "The name of output strong hypothesis (default: " + string(SHYP_NAME) + "." + string(SHYP_EXTENSION) + ").", 1, "<filename>");

   args.setGroup("Basic Algorithm Options");

   args.declareArgument("edgeoffset", "Defines the value of the edge offset (theta) (default: no edge offset).", 1, "<val>");
   args.declareArgument("resume", "Resumes a training process using the strong hypothesis file.", 1, "<shypFile>");
}

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

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

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

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

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

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

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

double BaseLearner::getAlpha(double eps_min, double eps_pls, 
                             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, 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