ErfVariable.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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// modification, are permitted provided that the following conditions are met:
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/* *******************************************************      
   * $Id: ErfVariable.cc,v 1.7 2004/07/21 16:30:54 chrish42 Exp $
   * This file is part of the PLearn library.
   ******************************************************* */

#include "ErfVariable.h"
#include "ExpVariable.h"
#include <plearn/math/pl_erf.h>
#include "Var_operators.h"
//#include "Var_utils.h"

namespace PLearn {
using namespace std;


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

ErfVariable::ErfVariable(Variable* input) 
  : inherited(input, input->length(), input->width())
{}

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

void ErfVariable::fprop()
{
  for(int i=0; i<nelems(); i++)
    valuedata[i] = pl_erf(input->valuedata[i]);
}


void ErfVariable::bprop()
{
  real cst = 2.0/sqrt(Pi);
  for(int i=0; i<nelems(); i++)
    input->gradientdata[i] += gradientdata[i] * cst*exp(input->valuedata[i]*input->valuedata[i]);
}


void ErfVariable::symbolicBprop()
{
  Var v(this);
  input->accg(g * 2.0/sqrt(Pi)*exp(square(input)));
}


} // end of namespace PLearn

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