Quad4F.h

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// @(#)root/minuit2:$Id: Quad4F.h 23073 2008-04-09 08:23:25Z moneta $
// Authors: M. Winkler, F. James, L. Moneta, A. Zsenei   2003-2005  

/**********************************************************************
 *                                                                    *
 * Copyright (c) 2005 LCG ROOT Math team,  CERN/PH-SFT                *
 *                                                                    *
 **********************************************************************/

#include "Minuit2/FCNGradientBase.h"

namespace ROOT {

   namespace Minuit2 {


class Quad4F : public FCNBase {

public:

  Quad4F() {}

  ~Quad4F() {}

  double operator()(const std::vector<double>& par) const {

    double x = par[0];
    double y = par[1];
    double z = par[2];
    double w = par[3];

    return ( (1./70.)*(21*x*x + 20*y*y + 19*z*z - 14*x*z - 20*y*z) + w*w );
  }

  double Up() const {return 1.;}

private:

};

// same function implementing the derivatives too 
class Quad4FGrad : public FCNGradientBase {

public:

  Quad4FGrad() {}

  ~Quad4FGrad() {}

  double operator()(const std::vector<double>& par) const {

    double x = par[0];
    double y = par[1];
    double z = par[2];
    double w = par[3];

    return ( (1./70.)*(21*x*x + 20*y*y + 19*z*z - 14*x*z - 20*y*z) + w*w );
  }

  std::vector<double> Gradient(const std::vector<double>& par) const {
    
    double x = par[0];
    double y = par[1];
    double z = par[2];
    double w = par[3];


    std::vector<double> g(4);
    g[0] = (1./70.) * ( 42. * x - 14. * z ); 
    g[1] = (1./70.) * ( 40. * y - 20. * z ); 
    g[2] = (1./70.) * ( 38. * z - 14. * x - 20. * y ); 
    g[3] = 2. * w; 
    return g;  
  }

  double Up() const {return 1.;}

private:

};


  }  // namespace Minuit2

}  // namespace ROOT

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