CbmRichRingFitterCOP.cxx

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/* Copyright (C) 2005-2012 GSI Helmholtzzentrum fuer Schwerionenforschung, Darmstadt
   SPDX-License-Identifier: GPL-3.0-only
   Authors: Alexander Ayriyan, Gennadi Ososkov, Semen Lebedev, Denis Bertini [committer] */
 
#include "CbmRichRingFitterCOP.h"
 
#include "CbmRichRingLight.h"
 
#include <cmath>
#include <iostream>
 
using namespace std;
 
CbmRichRingFitterCOP::CbmRichRingFitterCOP() {}
 
CbmRichRingFitterCOP::~CbmRichRingFitterCOP() {}
 
void CbmRichRingFitterCOP::DoFit(CbmRichRingLight* ring) { FitRing(ring); }
 
void CbmRichRingFitterCOP::FitRing(CbmRichRingLight* ring)
{
  int nofHits = ring->GetNofHits();
  if (nofHits < 3) {
    ring->SetRadius(0.);
    ring->SetCenterX(0.);
    ring->SetCenterY(0.);
    return;
  }
 
  if (nofHits >= MAX_NOF_HITS_IN_RING) {
    cout << "-E- CbmRichRingFitterCOP::DoFit(), too many hits in the ring:" << nofHits << endl;
    ring->SetRadius(0.);
    ring->SetCenterX(0.);
    ring->SetCenterY(0.);
    return;
  }
  int iterMax = 4;
  float Xi, Yi, Zi;
  float M0, Mx, My, Mz, Mxy, Mxx, Myy, Mxz, Myz, Mzz, Mxz2, Myz2, Cov_xy;
  float A0, A1, A2, A22;
  float epsilon = 0.00001;
  float Dy, xnew, xold, ynew, yold = 10000000.;
 
  M0 = nofHits;
  Mx = My = 0.;
 
  // calculate center of gravity
  for (int i = 0; i < nofHits; i++) {
    Mx += ring->GetHit(i).fX;
    My += ring->GetHit(i).fY;
  }
  Mx /= M0;
  My /= M0;
 
  // computing moments (note: all moments are normed, i.e. divided by N)
  Mxx = Myy = Mxy = Mxz = Myz = Mzz = 0.;
 
  for (int i = 0; i < nofHits; i++) {
    // transform to center of gravity coordinate system
    Xi = ring->GetHit(i).fX - Mx;
    Yi = ring->GetHit(i).fY - My;
    Zi = Xi * Xi + Yi * Yi;
 
    Mxy += Xi * Yi;
    Mxx += Xi * Xi;
    Myy += Yi * Yi;
    Mxz += Xi * Zi;
    Myz += Yi * Zi;
    Mzz += Zi * Zi;
  }
  Mxx /= M0;
  Myy /= M0;
  Mxy /= M0;
  Mxz /= M0;
  Myz /= M0;
  Mzz /= M0;
 
  //computing the coefficients of the characteristic polynomial
  Mz     = Mxx + Myy;
  Cov_xy = Mxx * Myy - Mxy * Mxy;
  Mxz2   = Mxz * Mxz;
  Myz2   = Myz * Myz;
 
  A2 = 4. * Cov_xy - 3. * Mz * Mz - Mzz;
  A1 = Mzz * Mz + 4. * Cov_xy * Mz - Mxz2 - Myz2 - Mz * Mz * Mz;
  A0 = Mxz2 * Myy + Myz2 * Mxx - Mzz * Cov_xy - 2. * Mxz * Myz * Mxy + Mz * Mz * Cov_xy;
 
  A22  = A2 + A2;
  xnew = 0.;
 
  //Newton's method starting at x=0
  int iter;
  for (iter = 0; iter < iterMax; iter++) {
    ynew = A0 + xnew * (A1 + xnew * (A2 + 4. * xnew * xnew));
 
    if (fabs(ynew) > fabs(yold)) {
      //  printf("Newton2 goes wrong direction: ynew=%f  yold=%f\n",ynew,yold);
      xnew = 0.;
      break;
    }
 
    Dy   = A1 + xnew * (A22 + 16. * xnew * xnew);
    xold = xnew;
    xnew = xold - ynew / Dy;
    //cout << " xnew = " << xnew ;
    if (xnew == 0 || fabs((xnew - xold) / xnew) < epsilon) {
      //cout << "iter = " << iter << " N = " << fNhits << endl;
      break;
    }
  }
 
  //if (iter == iterMax - 1) {
  //  printf("Newton2 does not converge in %d iterations\n",iterMax);
  //    xnew = 0.;
  //}
 
  float radius  = 0.;
  float centerX = 0.;
  float centerY = 0.;
 
  //computing the circle parameters
  float GAM = -Mz - xnew - xnew;
  float DET = xnew * xnew - xnew * Mz + Cov_xy;
  if (DET != 0.) {
    centerX = (Mxz * (Myy - xnew) - Myz * Mxy) / DET / 2.;
    centerY = (Myz * (Mxx - xnew) - Mxz * Mxy) / DET / 2.;
    radius  = sqrt(centerX * centerX + centerY * centerY - GAM);
    centerX += Mx;
    centerY += My;
  }
 
  ring->SetRadius(radius);
  ring->SetCenterX(centerX);
  ring->SetCenterY(centerY);
 
  CalcChi2(ring);
}