MucRecQuadFit Class Reference

#include <MucRecQuadFit.h>

List of all members.

Public Member Functions
	MucRecQuadFit ()
	Constructor.
	~MucRecQuadFit ()
	Destructor.
int	QuadFit (float x[], float y[], float w[], int n, float *a, float *b, float *c, int *half, float *chisq, float *siga, float *sigb, float *sigc)

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Detailed Description

Definition at line 15 of file MucRecQuadFit.h.

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Constructor & Destructor Documentation

MucRecQuadFit::MucRecQuadFit

(

)

Constructor.

Definition at line 21 of file MucRecQuadFit.cxx.

{
    // Constructor.
}

MucRecQuadFit::~MucRecQuadFit

(

)

Destructor.

Definition at line 26 of file MucRecQuadFit.cxx.

{
  // Destructor.
}

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Member Function Documentation

int MucRecQuadFit::QuadFit	(	float	x[],
		float	y[],
		float	w[],
		int	n,
		float *	a,
		float *	b,
		float *	c,
		int *	half,
		float *	chisq,
		float *	siga,
		float *	sigb,
		float *	sigc
	)

Definition at line 67 of file MucRecQuadFit.cxx.

References EvtCyclic3::ABC, EvtCyclic3::C, and genRecEmupikp::i.

Referenced by MucRec2DRoad::SimpleFit(), and MucRec2DRoad::SimpleFitNoCurrentGap().

                                                         : left 2 : right
                       float *chisq,
                       float *siga, 
                       float *sigb,
                       float *sigc)
  
{
  double sumx, sumx2, sumx3, sumx4,sumy, sumyx, sumyx2, det;
  float chi;
  
  /* The variable "i" is declared 8 bytes long to avoid triggering an
     apparent alignment bug in optimized code produced by gcc-2.95.3.
     The bug doesn't seem to be present in gcc-3.2. */
  long i; 

  chi = 99999999.0;
  *a = 0; *b = 0; *c = 0;
  *half = 0;

  /* N must be >= 2 for this guy to work */
  if (n < 3) 
    {
      //cout << "utiQuadFit-W: Too few points for quad fit \n" << endl;
      return -1;
    }

  /* Initialization */
  sumx  = 0.0;
  sumx2 = 0.0;
  sumx3 = 0.0;
  sumx4 = 0.0;
  sumy  = 0.0;
  sumyx = 0.0;
  sumyx2 = 0.0;


  /* Find sum , sumx ,sumy, sumxx, sumxy */
  for (i = 0; i < n; i++)
    {
      sumx = sumx + w[i] * x[i];
      sumx2 = sumx2 + w[i] * x[i] * x[i];
      sumx3 = sumx3 + w[i] * x[i] * x[i] * x[i];
      sumx4 = sumx4 + w[i] * x[i] * x[i] * x[i] * x[i];
      sumy = sumy + w[i] * y[i];
      sumyx = sumyx + w[i] * y[i] * x[i];
      sumyx2 = sumyx2 + w[i] * y[i] * x[i] * x[i];      
      //cout<<"x : y "<<x[i]<<" "<<y[i]<<endl;

    }



  /* compute the best fitted parameters A,B,C */

    HepMatrix D(3,3,1);
    HepMatrix C(3,1), ABC(3,1);
    D(1,1) = sumx4; D(1,2) = D(2,1) = sumx3; D(1,3) = D(3,1) = D(2,2) = sumx2;
    D(3,2) = D(2,3) = sumx; D(3,3) = n;
    C(1,1) = sumyx2; C(2,1) = sumyx; C(3,1) = sumy;

    int ierr;
    ABC = (D.inverse(ierr))*C;

    *a = ABC(1,1);
    *b = ABC(2,1);
    *c = ABC(3,1);
    
    //judge which half parabola these points belone to
    float center = *b/(-2*(*a));
    float mean_x;
    for(i = 0; i < n; i++){
      mean_x += x[i]/n;
    }

    if(mean_x > center) *half = 2;//right half
    else *half = 1;//left half
    
    //cout<<"in MucRecQuadFit:: which half= "<<*half<<endl;

  /* calculate chi-square */
  chi = 0.0;
  for (i=0; i<n; i++) 
    {
      chi = chi+(w[i])*((y[i])-*a*(x[i])-*b)*
        ((y[i])-*a*(x[i])-*b);
    }
  
  //*siga = sum/det;
  //*sigb = sxx/det;
  
  *chisq = chi;
  return 1;
}   

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