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

  Program:   Insight Segmentation & Registration Toolkit
  Module:    $RCSfile: itkForwardDifferenceOperator.h,v $
  Language:  C++
  Date:      $Date: 2003/09/10 14:29:08 $
  Version:   $Revision: 1.16 $

  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 __itkForwardDifferenceOperator_h
#define __itkForwardDifferenceOperator_h

#include "itkNeighborhoodOperator.h"
#include "itkExceptionObject.h"

namespace itk {

/**  
 * \class ForwardDifferenceOperator
 * \brief Operator whose inner product with a neighborhood returns
 * a "half" derivative at the center of the neighborhood.
 *
 * ForwardDifferenceOperator uses forward differences
 * i.e. F(x+1) - F(x) to calculate a "half" derivative useful, among
 * other things, in solving differential equations. It is a directional
 * NeighborhoodOperator that should be applied to a Neighborhood using the
 * inner product.
 *
 * \ingroup Operators
 */
template<class TPixel, unsigned int VDimension=2,
  class TAllocator = NeighborhoodAllocator<TPixel> >
class ITK_EXPORT ForwardDifferenceOperator
  : public NeighborhoodOperator<TPixel, VDimension, TAllocator>
{
public:
  /** Standard class typedefs. */
  typedef ForwardDifferenceOperator Self;
  typedef NeighborhoodOperator<TPixel, VDimension, TAllocator> Superclass;
  
  typedef typename Superclass::PixelType PixelType;

  /** Constructor. */
  ForwardDifferenceOperator() {}

  /** Copy constructor */
  ForwardDifferenceOperator(const Self& other)
    : NeighborhoodOperator<TPixel, VDimension, TAllocator>(other)
  {  }

  /** Assignment operator */
  Self &operator=(const Self& other)
  {
    Superclass::operator=(other);
    return *this;
  }
  
protected:
  /** Necessary to work around VC++ compiler bug. */
  typedef typename Superclass::CoefficientVector CoefficientVector;
  
  /** Calculates operator coefficients. */
  CoefficientVector GenerateCoefficients();
  
  /** Arranges coefficients spatially in the memory buffer. */
  void Fill(const CoefficientVector &coeff)

    { this->FillCenteredDirectional(coeff); }

};
  

} // namespace itk

#ifndef ITK_MANUAL_INSTANTIATION
#include "itkForwardDifferenceOperator.txx"
#endif

#endif


