LiftOutputVariable.cc

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// -*- C++ -*-

// PLearn (A C++ Machine Learning Library)
// Copyright (C) 2003 Olivier Delalleau

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// modification, are permitted provided that the following conditions are met:
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// 
// THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
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// This file is part of the PLearn library. For more information on the PLearn
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/* *******************************************************      
   * $Id: LiftOutputVariable.cc,v 1.6 2004/04/27 15:58:16 morinf Exp $
   * This file is part of the PLearn library.
   ******************************************************* */

#include "LiftOutputVariable.h"

namespace PLearn {
using namespace std;

PLEARN_IMPLEMENT_OBJECT(
  LiftOutputVariable,
  "The result is the output if the target is 1, and the opposite of the output "
  "otherwise. This variable is to be used with a LiftStatsCollector, in a"
  "stochastic gradient descent.",
  "NO HELP"
);

// LiftOutputVariable //
LiftOutputVariable::LiftOutputVariable(Variable* netout, Variable* target)
  : inherited(netout,target,1,1)
{
    build_();
}

void
LiftOutputVariable::build()
{
    inherited::build();
    build_();
}

void
LiftOutputVariable::build_()
{
    if (input1 && input2) {
        // input1 and input2 are (respectively) netout and target from the constructor
        if(input1->size() != input2->size())
            PLERROR("In LiftOutputVariable: netout and target must have the same size");
    }
}

// recomputeSize //
void LiftOutputVariable::recomputeSize(int& l, int& w) const
{ l=1, w=1; }

// fprop //
void LiftOutputVariable::fprop()
{
  real output = input1->valuedata[0];
  real target = input2->valuedata[0];
  if (target == 1.0) {
    if (output == 0.0) {
      // We need to make sure the output is positive.
      output = 1e-10;
    }
    valuedata[0] = output;
  } else {
    valuedata[0] = -output;
  }
}

void LiftOutputVariable::bprop()
{
  // TODO Not really sure what to do here, bprop shouldn't be used anyway.
  // Actually it IS called, should investigate why and what it does.
  // PLWARNING("In LiftOutputVariable::bprop - You should not backprop on a LiftOutputVariable");
  real gr = *gradientdata;
  for (int i=0; i<input1->size(); i++)
  {
    input1->gradientdata[i] += gr;
  }
}

} // end of namespace PLearn

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