HardSlopeVariable.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:
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//  1. Redistributions of source code must retain the above copyright
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/* *******************************************************      
   * $Id: HardSlopeVariable.h,v 1.6 2004/04/27 16:02:26 morinf Exp $
   * This file is part of the PLearn library.
   ******************************************************* */

#ifndef HardSlopeVariable_INC
#define HardSlopeVariable_INC

#include "NaryVariable.h"
#include "Var_operators.h"
#include "Var_all.h"

namespace PLearn {
using namespace std;


// linear by part function that
// is 0 in [-infty,left], linear in [left,right], and 1 in [right,infty].
class HardSlopeVariable: public NaryVariable
{
  typedef NaryVariable inherited;

public:
  HardSlopeVariable() {}
  HardSlopeVariable(Variable* x, Variable* left, Variable* right);

  PLEARN_DECLARE_OBJECT(HardSlopeVariable);

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

DECLARE_OBJECT_PTR(HardSlopeVariable);

inline Var hard_slope(Var x, Var left, Var right)
{ return new HardSlopeVariable(x,left,right); }

// derivative of hard_slope wrt x
inline Var d_hard_slope(Var x, Var left, Var right)
{
  return ifThenElse((x>=left)*(x<=right), invertElements(right-left), var(0.0));
}

} // end of namespace PLearn

#endif 

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