itkAtanRegularizedHeavisideStepFunction.h

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/*=========================================================================

  Program:   Insight Segmentation & Registration Toolkit
  Module:    $RCSfile: itkAtanRegularizedHeavisideStepFunction.h,v $
  Language:  C++
  Date:      $Date: 2009-05-09 21:12:23 $
  Version:   $Revision: 1.2 $

  Copyright (c) Insight Software Consortium. All rights reserved.
  See ITKCopyright.txt or http://www.itk.org/HTML/Copyright.htm for details.

     This software is distributed WITHOUT ANY WARRANTY; without even
     the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
     PURPOSE.  See the above copyright notices for more information.

=========================================================================*/

#ifndef __itkAtanRegularizedHeavisideStepFunction_h
#define __itkAtanRegularizedHeavisideStepFunction_h

#include "itkRegularizedHeavisideStepFunction.h"

namespace itk
{

template< class TInput = float, class TOutput = double >
class AtanRegularizedHeavisideStepFunction : 
 public RegularizedHeavisideStepFunction< TInput, TOutput >
{
public:
  typedef AtanRegularizedHeavisideStepFunction                  Self;
  typedef RegularizedHeavisideStepFunction< TInput, TOutput >   Superclass;
  typedef SmartPointer<Self>                                    Pointer;
  typedef SmartPointer<const Self>                              ConstPointer;

  itkNewMacro( Self );
 
  itkTypeMacro( AtanRegularizedHeavisideStepFunction, RegularizedHeavisideStepFunction );

  typedef typename Superclass::InputType                        InputType;
  typedef typename Superclass::OutputType                       OutputType;
  typedef typename Superclass::RealType                         RealType;

  virtual OutputType Evaluate( const InputType& input ) const
    {
    return 0.5 + ( vnl_math::one_over_pi * vcl_atan( input * this->GetOneOverEpsilon() ) );
    }

  virtual OutputType EvaluateDerivative( const InputType& input ) const
    {
    const RealType t = ( input * this->GetOneOverEpsilon() );
    return static_cast< OutputType>( vnl_math::one_over_pi / (1.0 + t * t ) );
    }

protected:
  AtanRegularizedHeavisideStepFunction() {}
  virtual ~AtanRegularizedHeavisideStepFunction() {}

private:
  AtanRegularizedHeavisideStepFunction(const Self& ); //purposely not implemented
  void operator=(const Self& ); //purposely not implemented

};

}

#endif