ClassErrorCostFunction.cc

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// -*- C++ -*-

// PLearn (A C++ Machine Learning Library)
// Copyright (C) 1998 Pascal Vincent
// Copyright (C) 1999-2002 Pascal Vincent, Yoshua Bengio, Rejean Ducharme and University of Montreal
// Copyright (C) 2001-2002 Nicolas Chapados, Ichiro Takeuchi, Jean-Sebastien Senecal
// Copyright (C) 2002 Xiangdong Wang, Christian Dorion

// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
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//  1. Redistributions of source code must retain the above copyright
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/* *******************************************************      
   * $Id: ClassErrorCostFunction.cc,v 1.4 2004/04/07 23:15:17 morinf Exp $
   * This file is part of the PLearn library.
   ******************************************************* */

#include "ClassErrorCostFunction.h"

namespace PLearn {
using namespace std;


// **** ClassErrorCostFunction ****

PLEARN_IMPLEMENT_OBJECT(ClassErrorCostFunction, "ONE LINE DESCR", "NO HELP");

real ClassErrorCostFunction::evaluate(const Vec& output, const Vec& target) const
{
  if(output_is_classnum)
  {
    if(is_integer(output[0]))
      return output[0]==target[0] ?0 :1;
    else if(target[0]==1.)
      return output[0]>0.5 ?0 :1;
    else // target[0]==0 or -1
      return output[0]<=0.5 ?0 :1;
  }

  if(output.length()==1) // we assume the sign of output indicates the chosen class 
  {
    if(target[0]>0)
      return output[0]>0 ?0. :1.;
    else
      return output[0]<0 ?0. :1.;
  }
  else // we assume output gives a score for each class
  {
    int trueclass;
    if(target.length()==1)
      trueclass = int(target[0]);
    else
      trueclass = argmax(target);
    return argmax(output)==trueclass ?0. :1.;
  }
  return 1.; // to make the compiler happy
}

void
ClassErrorCostFunction::declareOptions(OptionList &ol)
{
    declareOption(ol, "output_is_classnum", &ClassErrorCostFunction::output_is_classnum, OptionBase::buildoption, "Output of learner is class number");
    inherited::declareOptions(ol);
}



} // end of namespace PLearn

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