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DiagonalPreconditioner.h

/****************************************************************************
 *                                                                          *
 *  Program: FDDlib                                                         *
 *  Version: 1.1                                                            *
 *                                                                          *
 *  Copyright (C) 2002 - 2004 by Eric Miller and Dana Brooks                *
 *  All rights reserved.                                                    *
 *                                                                          *
 *  This software is Version 1.1 of the fddlib tomography toolbox.          *
 *  It is not to be redistributed or used for any commercial purpose        *
 *  without the prior written consent of the authors and Northeastern       *
 *  University.                                                             *
 *                                                                          *
 *  This software is provided as is, and any express or implied warranties, *
 *  including but not limited to the implied warranty of merchantability    *
 *  and the implied warranty of fitness for a particular purpose, are dis-  *
 *  claimed.  In no event shall the authors or Northeastern University be   *
 *  liable for any direct, indirect, incidental, special, exemplary, or     *
 *  consequential damages (including but not limited to procurement of      * 
 *  substitute goods or services; loss of use, data, or profits; or busi-   *
 *  ness interruption) however caused and on any theory of liability,       *
 *  whether in contract, strict liability, or tort (including negligence or *
 *  otherwise) arising in any way from the use of this software, even if    *
 *  advised of the possibility of such damage.                              *
 *                                                                          *
 *  Portions of this code benefit from ideas from Kyle Guilbert, Greg       *
 *  Boverman, Derek Uluski, David Kaeli, and Jennifer Black                 *
 *                                                                          *
 ****************************************************************************/

#ifndef _DIAGONAL_PRECONDITIONER_H_
#define _DIAGONAL_PRECONDITIONER_H_

#include "Preconditioner.h"
#include "SparseRowMatrix.h"
#include "RealVector.h"
#include <string>

namespace FDDlib {

class DiagonalPreconditioner : public Preconditioner
{
private:
  double*   invDiag_;

public:

  DiagonalPreconditioner(SparseRowMatrix<double>& SRMD)
  {
    int i;

    len_ = SRMD.getNumRows();
    invDiag_ = new double[len_];
    for (i = 0; i < len_; i++)
    {
      invDiag_[i] = 1 / SRMD.val(i,i);
    }
  }

  DiagonalPreconditioner()
  {
    len_ = 0;
    invDiag_ = (double*) NULL;
  }

  void init(SparseRowMatrix<double>& SRMD) throw(std::string)
  {
    int i;

    len_ = SRMD.getNumRows();
    if (invDiag_ != (double*) NULL)
      delete invDiag_;
    invDiag_ = new double[len_];
    for (i = 0; i < len_; i++)
    {
      if (SRMD.val(i,i) == 0)
        throw std::string("DiagonalPreconditioner::init: zero on matrix diagonal.");
      invDiag_[i] = 1 / SRMD.val(i,i);
    }
  }

  ~DiagonalPreconditioner()
  {
    if (invDiag_ != (double*) NULL)
      delete[] invDiag_;
  }

  RealVector<double> solve(const RealVector<double>& x) const
  {

    RealVector<double> r(len_);
    int    i;

    for (i = 0; i < len_; i++)
    {
      r(i) = invDiag_[i]*x(i);
    }

    return r;
  }



};

// end namespace
}  
#endif

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