DivVariable.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

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/* *******************************************************      
   * $Id: DivVariable.cc,v 1.6 2004/04/27 15:58:16 morinf Exp $
   * This file is part of the PLearn library.
   ******************************************************* */

#include "DivVariable.h"
#include "InvertElementsVariable.h"
#include "Var_operators.h"

namespace PLearn {
using namespace std;


PLEARN_IMPLEMENT_OBJECT(DivVariable,
                        "Divide 2 matrix vars of same size elementwise",
                        "NO HELP");

DivVariable::DivVariable(Variable* input1, Variable* input2)
  : BinaryVariable(input1, input2, input1->length(), input1->width())
{
    build_();
}


void DivVariable::recomputeSize(int& l, int& w) const
{
    if (input1) {
        l = input1->length();
        w = input1->width();
    } else
        l = w = 0;
}

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

void
DivVariable::build_()
{
    if (input1 && input2)
        if(input1->length() != input2->length() || input1->width() != input2->width())
            PLERROR("In DivVariable: input1 and input2 must have exactly the same shape");
}

void DivVariable::fprop()
{
  for(int k=0; k<nelems(); k++)
    valuedata[k] = input1->valuedata[k]/input2->valuedata[k];
}


void DivVariable::bprop()
{
  for(int k=0; k<nelems(); k++)
    {
      real iv2k = 1.0/input2->valuedata[k];
      input1->gradientdata[k] += gradientdata[k] * iv2k;
      input2->gradientdata[k] -= gradientdata[k] * 
        input1->valuedata[k] * iv2k * iv2k;
    }
}


void DivVariable::symbolicBprop()
{
  Var iv2 = invertElements(input2);
  input1->accg(g * iv2);
  input2->accg(-g * input1 * square(iv2));
}


void DivVariable::rfprop()
{
  if (rValue.length()==0) resizeRValue();
  
  for(int k=0; k<nelems(); k++)
    {
      real iv2k = 1.0/input2->valuedata[k];
      rvaluedata[k] = input1->rvaluedata[k] * iv2k - input2->rvaluedata[k] * input1->valuedata[k] * iv2k * iv2k;
    }
}



} // end of namespace PLearn

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