MarginPerceptronCostVariable.h

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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:
// 
//  1. Redistributions of source code must retain the above copyright
//     notice, this list of conditions and the following disclaimer.
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/* *******************************************************      
   * $Id: MarginPerceptronCostVariable.h,v 1.2 2004/04/27 16:03:35 morinf Exp $
   * This file is part of the PLearn library.
   ******************************************************* */

#ifndef MarginPerceptronCostVariable_INC
#define MarginPerceptronCostVariable_INC

#include "BinaryVariable.h"

namespace PLearn {
using namespace std;

  // cost = sum_i max(0,margin - signed_target[i]*output[i])
  // where signed_target is inferred from target as follows.
  // target must be in (0,1,...,nclasses-1).
  // If output.size()==1, signed_target[0] = target*2-1
  // else signed_target[i] = 1_{target==i} - 1_{target!=i}.
class MarginPerceptronCostVariable: public BinaryVariable
{
  typedef BinaryVariable inherited;

protected:  
  real margin;
  
public:
  MarginPerceptronCostVariable() {}
  MarginPerceptronCostVariable(Variable* output, Variable* target, real margin);

  PLEARN_DECLARE_OBJECT(MarginPerceptronCostVariable);
  static void declareOptions(OptionList &ol);

  virtual void build();

  virtual void recomputeSize(int& l, int& w) const;
  virtual void fprop();
  virtual void bprop();

protected:
  void build_();
};

DECLARE_OBJECT_PTR(MarginPerceptronCostVariable);

inline Var margin_perceptron_cost(Var output, Var target, real margin)
{
  return new MarginPerceptronCostVariable(output, target, margin);
}

} // end of namespace PLearn

#endif 

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