CbmRichRingFitterEllipseMinuit.cxx

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/* Copyright (C) 2011-2020 UGiessen/JINR-LIT, Giessen/Dubna
   SPDX-License-Identifier: GPL-3.0-only
   Authors: Semen Lebedev [committer], Florian Uhlig */
 
#include "CbmRichRingFitterEllipseMinuit.h"
 
#include "Minuit2/Minuit2Minimizer.h"
 
#include <Logger.h>
 
using std::cout;
using std::endl;
 
CbmRichRingFitterEllipseMinuit::CbmRichRingFitterEllipseMinuit() {}
 
CbmRichRingFitterEllipseMinuit::~CbmRichRingFitterEllipseMinuit() {}
 
void CbmRichRingFitterEllipseMinuit::DoFit(CbmRichRingLight* ring)
{
  int nofHits = ring->GetNofHits();
 
  if (nofHits <= 5) {
    ring->SetXYABP(-1., -1., -1., -1., -1.);
    ring->SetRadius(-1.);
    return;
  }
 
  vector<double> hitX;
  vector<double> hitY;
  hitX.clear();
  hitY.clear();
  for (int i = 0; i < nofHits; i++) {
    hitX.push_back(ring->GetHit(i).fX);
    hitY.push_back(ring->GetHit(i).fY);
  }
 
  vector<double> fpar = DoFit(hitX, hitY);
 
  TransformToRichRing(ring, fpar);
 
  CalcChi2(ring);
}
 
void CbmRichRingFitterEllipseMinuit::TransformToRichRing(CbmRichRingLight* ring, const vector<double>& fpar)
{
  // calculate center of the ellipse
  double xc = (fpar[0] + fpar[2]) / 2.;
  double yc = (fpar[1] + fpar[3]) / 2.;
  // calculate length of b axes
  double p1 = (fpar[0] - fpar[2]) * (fpar[0] - fpar[2]) + (fpar[1] - fpar[3]) * (fpar[1] - fpar[3]);
  if (p1 < 0.) {
    ring->SetXYABP(-1., -1., -1., -1., -1.);
    ring->SetRadius(-1.);
    return;
  }
 
  double c  = sqrt(p1) / 2.;
  double p2 = fpar[4] * fpar[4] - c * c;
  if (p2 < 0.) {
    ring->SetXYABP(-1., -1., -1., -1., -1.);
    ring->SetRadius(-1.);
    return;
  }
  double b = sqrt(p2);
  // calculate angle
  double p3 = fpar[2] - fpar[0];
  if (p3 == 0.) {
    ring->SetXYABP(-1., -1., -1., -1., -1.);
    ring->SetRadius(-1.);
    return;
  }
  double k   = (fpar[3] - fpar[1]) / (fpar[2] - fpar[0]);
  double ang = atan(k);
 
  ring->SetXYABP(xc, yc, fpar[4], b, ang);
  ring->SetRadius((b + fpar[4]) / 2.);
}
 
vector<double> CbmRichRingFitterEllipseMinuit::DoFit(const vector<double>& x, const vector<double>& y)
{
 
  // Create initial starting values for parameters
  double xf1 = 0.;
  double yf1 = 0.;
  for (unsigned int i = 0; i < x.size(); i++) {
    xf1 += x[i];
    yf1 += y[i];
  }
  double a   = 5.;
  xf1        = xf1 / x.size() - a;
  yf1        = yf1 / x.size();
  double xf2 = xf1 + a;
  double yf2 = yf1;
 
 
  ROOT::Minuit2::Minuit2Minimizer min;
 
 
  FCNEllipse2* theFCN = new FCNEllipse2(x, y);
 
  min.SetMaxFunctionCalls(1000000);
  min.SetMaxIterations(100000);
  min.SetTolerance(0.001);
 
  min.SetFunction(*theFCN);
 
  // Set the free variables to be minimized!
  min.SetVariable(0, "xf1", xf1, 0.1);
  min.SetVariable(1, "yf1", yf1, 0.1);
  min.SetVariable(2, "xf2", xf2, 0.1);
  min.SetVariable(3, "yf2", yf2, 0.1);
  min.SetVariable(4, "a", a, 0.1);
 
  min.Minimize();
 
  const double* xs = min.X();
 
  vector<double> fpar;
  fpar.clear();
  for (int i = 0; i < 5; i++) {
    fpar.push_back(xs[i]);
  }
  return fpar;
}