DTLinearFit.cc

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/* This Class Header */
#include "RecoLocalMuon/DTSegment/src/DTLinearFit.h"
 
/* Collaborating Class Header */
 
/* C++ Headers */
#include <cmath>
using namespace std;
 
/* ====================================================================== */
 
DTLinearFit::DTLinearFit() {}
 
DTLinearFit::~DTLinearFit() {}
 
/* Operations */
void DTLinearFit::fit(const vector<float>& x,
                      const vector<float>& y,
                      int nptfit,
                      const vector<float>& sigy,
                      float& slope,
                      float& intercept,
                      double& chi2,
                      float& covss,
                      float& covii,
                      float& covsi) const {
  chi2 = 0;
  float sy = 0, sx = 0;
  float s11 = 0, sxy = 0, sxx = 0;
  for (int i = 0; i != nptfit; i++) {
    float sy2 = sigy[i] * sigy[i];
    sy += y[i] / sy2;
    sxy += x[i] * y[i] / sy2;
    s11 += 1. / sy2;
    sx += x[i] / sy2;
    sxx += x[i] * x[i] / sy2;
  }
 
  float delta = s11 * sxx - sx * sx;
 
  if (delta == 0)
    return;
 
  intercept = (sy * sxx - sxy * sx) / delta;
  slope = (sxy * s11 - sy * sx) / delta;
 
  covii = sxx / delta;
  covss = s11 / delta;
  covsi = -sx / delta;
 
  for (int j = 0; j < nptfit; j++) {
    const double ypred = intercept + slope * x[j];
    const double dy = (y[j] - ypred) / sigy[j];
    chi2 += dy * dy;
  }
}
 
void DTLinearFit::fitNpar(const int npar,
                          const vector<float>& xfit,
                          const vector<float>& yfit,
                          const vector<int>& lfit,
                          const vector<double>& tfit,
                          const vector<float>& sigy,
                          float& aminf,
                          float& bminf,
                          float& cminf,
                          float& vminf,
                          double& chi2fit,
                          const bool debug = false) const {
  int nptfit = xfit.size();
  if (nptfit < npar)
    return;
 
  double sx = 0.;
  double sxx = 0.;
  double sy = 0.;
  double sxy = 0.;
  double sl = 0.;
  double sl2 = 0.;
  double sly = 0.;
  double slx = 0.;
  double st = 0.;
  double st2 = 0.;
  double slt = 0.;
  double sltx = 0.;
  double slty = 0.;
 
  for (int j = 0; j < nptfit; j++) {
    sx += xfit[j];
    sy += yfit[j];
    sxx += xfit[j] * xfit[j];
    sxy += xfit[j] * yfit[j];
    sl += lfit[j];
    sl2 += lfit[j] * lfit[j];
    sly += lfit[j] * yfit[j];
    slx += lfit[j] * xfit[j];
    st += tfit[j];
    st2 += tfit[j] * tfit[j];
    slt += lfit[j] * tfit[j];
    sltx += lfit[j] * tfit[j] * xfit[j];
    slty += lfit[j] * tfit[j] * yfit[j];
  }  //end loop
 
  const double d1 = sy;
  const double d2 = sxy;
  const double d3 = sly;
  const double c1 = sl;
  const double c2 = slx;
  const double c3 = sl2;
  const double b1 = sx;
  const double b2 = sxx;
  const double b3 = slx;
  const double a1 = nptfit;
  const double a2 = sx;
  const double a3 = sl;
 
  const double b4 = b2 * a1 - b1 * a2;
  const double c4 = c2 * a1 - c1 * a2;
  const double d4 = d2 * a1 - d1 * a2;
  const double b5 = a1 * b3 - a3 * b1;
  const double c5 = a1 * c3 - a3 * c1;
  const double d5 = a1 * d3 - d1 * a3;
  const double a6 = slt;
  const double b6 = sltx;
  const double c6 = st;
  const double v6 = st2;
  const double d6 = slty;
 
  chi2fit = -1.;
 
  if (npar == 3) {
    if (((c5 * b4 - c4 * b5) * b4 * a1) != 0) {
      cminf = (d5 * b4 - d4 * b5) / (c5 * b4 - c4 * b5);
      if (fabs(cminf) < 0.000001)
        cminf = 0;
      aminf = d4 / b4 - cminf * c4 / b4;
      bminf = (d1 / a1 - cminf * c1 / a1 - aminf * b1 / a1);
 
      chi2fit = 0.;
      for (int j = 0; j < nptfit; j++) {
        const double ypred = aminf * xfit[j] + bminf;
        const double ycorr = yfit[j] - cminf * lfit[j];
        const double dy = (ycorr - ypred) / sigy[j];
        chi2fit += dy * dy;
 
        if (tfit[j] == 0.)
          continue;
        double xwire = yfit[j] - tfit[j];
 
        // define a small safety margin
        double margin = 0.1;
        //          cout << " pred: " << ypred << "  hit: " << ycorr << "chi2: " << dy*dy << " t0: " << -cminf/0.00543 << endl;
 
        // Sanity checks - check that the hit after the fit is still withing the DT cell volume
        if ((fabs(yfit[j] - xwire) > margin) && (fabs(ycorr - xwire) > margin) &&
            ((yfit[j] - xwire) * (ycorr - xwire) < 0)) {
          //          cout << " segmentpred: " << ypred << "   hit: " << ycorr << "   xwire: " << xwire << "   yhit: " << yfit[j] << "   t0: " << -cminf/0.00543 << endl;
          //          cout << " XXX hit moved across wire!!!" << endl;
          chi2fit = -1.;
          return;
        }
 
        if (fabs(ypred - xwire) > 2.1 + margin) {
          //          cout << " segmentpred: " << ypred << "   hit: " << ycorr << "   xwire: " << xwire << "   yhit: " << yfit[j] << "   t0: " << -cminf/0.00543 << endl;
          //          cout << " XXX segment outside chamber!!!" << endl;
          chi2fit = -1.;
          return;
        }
 
        if (fabs(ycorr - xwire) > 2.1 + margin) {
          //          cout << " segmentpred: " << ypred << "   hit: " << ycorr << "   xwire: " << xwire << "   yhit: " << yfit[j] << "   t0: " << -cminf/0.00543 << endl;
          //          cout << " XXX hit outside chamber!!!" << endl;
          chi2fit = -1.;
          return;
        }
        if (fabs(chi2fit < 0.0001))
          chi2fit = 0;
      }  //end loop chi2
    }
  } else if (npar == 4) {
    const double det =
        (a1 * a1 * (b2 * v6 - b6 * b6) -
         a1 * (a2 * a2 * v6 - 2 * a2 * a6 * b6 + a6 * a6 * b2 + b2 * c6 * c6 + b3 * (b3 * v6 - 2 * b6 * c6)) +
         a2 * a2 * c6 * c6 + 2 * a2 * (a3 * (b3 * v6 - b6 * c6) - a6 * b3 * c6) + a3 * a3 * (b6 * b6 - b2 * v6) +
         a6 * (2 * a3 * (b2 * c6 - b3 * b6) + a6 * b3 * b3));
 
    if (det != 0) {
      // computation of a, b, c and v
      bminf = (a1 * (a2 * (b6 * d6 - v6 * d2) + a6 * (b6 * d2 - b2 * d6) + d1 * (b2 * v6 - b6 * b6)) -
               a2 * (b3 * (c6 * d6 - v6 * d3) + c6 * (b6 * d3 - c6 * d2)) +
               a3 * (b2 * (c6 * d6 - v6 * d3) + b3 * (v6 * d2 - b6 * d6) + b6 * (b6 * d3 - c6 * d2)) +
               a6 * (b2 * c6 * d3 + b3 * (b3 * d6 - b6 * d3 - c6 * d2)) -
               d1 * (b2 * c6 * c6 + b3 * (b3 * v6 - 2 * b6 * c6))) /
              det;
      aminf =
          -(a1 * a1 * (b6 * d6 - v6 * d2) -
            a1 * (a2 * (a6 * d6 - v6 * d1) - a6 * a6 * d2 + a6 * b6 * d1 + b3 * (c6 * d6 - v6 * d3) +
                  c6 * (b6 * d3 - c6 * d2)) +
            a2 * (a3 * (c6 * d6 - v6 * d3) + c6 * (a6 * d3 - c6 * d1)) + a3 * a3 * (v6 * d2 - b6 * d6) +
            a3 * (a6 * (b3 * d6 + b6 * d3 - 2 * c6 * d2) - d1 * (b3 * v6 - b6 * c6)) - a6 * b3 * (a6 * d3 - c6 * d1)) /
          det;
      cminf = -(a1 * (b2 * (c6 * d6 - v6 * d3) + b3 * (v6 * d2 - b6 * d6) + b6 * (b6 * d3 - c6 * d2)) +
                a2 * a2 * (v6 * d3 - c6 * d6) +
                a2 * (a3 * (b6 * d6 - v6 * d2) + a6 * (b3 * d6 - 2 * b6 * d3 + c6 * d2) - d1 * (b3 * v6 - b6 * c6)) +
                a3 * (d1 * (b2 * v6 - b6 * b6) - a6 * (b2 * d6 - b6 * d2)) +
                a6 * (a6 * (b2 * d3 - b3 * d2) - d1 * (b2 * c6 - b3 * b6))) /
              det;
      vminf = -(a1 * a1 * (b2 * d6 - b6 * d2) -
                a1 * (a2 * a2 * d6 - a2 * (a6 * d2 + b6 * d1) + a6 * b2 * d1 + b2 * c6 * d3 +
                      b3 * (b3 * d6 - b6 * d3 - c6 * d2)) +
                a2 * a2 * c6 * d3 + a2 * (a3 * (2 * b3 * d6 - b6 * d3 - c6 * d2) - b3 * (a6 * d3 + c6 * d1)) +
                a3 * a3 * (b6 * d2 - b2 * d6) + a3 * (a6 * (b2 * d3 - b3 * d2) + d1 * (b2 * c6 - b3 * b6)) +
                a6 * b3 * b3 * d1) /
              det;
 
      chi2fit = 0.;
      for (int j = 0; j < nptfit; j++) {
        const double ypred = aminf * xfit[j] + bminf;
        const double dy = (yfit[j] + vminf * lfit[j] * tfit[j] - cminf * lfit[j] - ypred) / sigy[j];
        chi2fit += dy * dy;
      }  //end loop chi2
    }
  }
}
 
void DTLinearFit::fit3par(const vector<float>& xfit,
                          const vector<float>& yfit,
                          const vector<int>& lfit,
                          const int nptfit,
                          const vector<float>& sigy,
                          float& aminf,
                          float& bminf,
                          float& cminf,
                          double& chi2fit,
                          const bool debug = false) const {
  float vminf;
  vector<double> tfit(nptfit, 0.);
 
  fitNpar(3, xfit, yfit, lfit, tfit, sigy, aminf, bminf, cminf, vminf, chi2fit, debug);
}
 
void DTLinearFit::fit4Var(const vector<float>& xfit,
                          const vector<float>& yfit,
                          const vector<int>& lfit,
                          const vector<double>& tfit,
                          const int nptfit,
                          float& aminf,
                          float& bminf,
                          float& cminf,
                          float& vminf,
                          double& chi2fit,
                          const bool vdrift_4parfit = false,
                          const bool debug = false) const {
  if (debug)
    cout << "Entering Fit4Var" << endl;
 
  const double sigma =
      0.0295;  // FIXME errors can be inserted .just load them/that is the usual TB resolution value for DT chambers
  vector<float> sigy;
 
  aminf = 0.;
  bminf = 0.;
  cminf = -999.;
  vminf = 0.;
 
  int nppar = 0;
  double chi2fitN2 = -1.;
  double chi2fit3 = -1.;
  double chi2fitN3 = -1.;
  double chi2fitN4 = -1.;
  int nppar2 = 0;
  int nppar3 = 0;
  int nppar4 = 0;
 
  for (int j = 0; j < nptfit; j++)
    sigy.push_back(sigma);
 
  float a = 0.;
  float b = 0.;
  float covss, covii, covsi;
 
  fit(xfit, yfit, nptfit, sigy, b, a, chi2fit, covss, covii, covsi);
 
  bminf = b;
  aminf = a;
  nppar = 2;
  nppar2 = nppar;
  chi2fitN2 = chi2fit / (nptfit - nppar);
 
  // cout << "dt0 = 0  chi2fit = " << chi2fit << "  slope = "<<b<<endl;
 
  if (nptfit >= 3) {
    fitNpar(3, xfit, yfit, lfit, tfit, sigy, bminf, aminf, cminf, vminf, chi2fit, debug);
    chi2fit3 = chi2fit;
 
    if (cminf != -999.) {
      nppar = 3;
    } else {
      bminf = b;
      aminf = a;
    }
    chi2fitN3 = (nptfit > nppar) ? chi2fit / (nptfit - nppar) : -1.;
 
    float aminf3 = aminf;
    float bminf3 = bminf;
    float cminf3 = cminf;
    nppar3 = nppar;
 
    if (debug) {
      cout << "dt0= 0 : slope 2 = " << b << " pos in  = " << a << " chi2fitN2 = " << chi2fitN2 << " nppar = " << nppar2
           << " nptfit = " << nptfit << endl;
      cout << "dt0 = 0 : slope 3 = " << bminf << " pos out = " << aminf << " chi2fitN3 = " << chi2fitN3
           << " nppar = " << nppar3 << " T0_ev ns = " << cminf / 0.00543 << endl;
      cout << " vdrift_4parfit " << vdrift_4parfit << endl;
    }
 
    if (nptfit >= 5) {
      fitNpar(4, xfit, yfit, lfit, tfit, sigy, bminf, aminf, cminf, vminf, chi2fit, debug);
 
      if (vminf != 0)
        nppar = 4;
 
      chi2fitN4 = (nptfit > nppar) ? chi2fit / (nptfit - nppar) : -1.;
 
      if (fabs(vminf) >= 0.29) {
        // for safety and for code construction..dont accept correction on dv/vdrift greater then 0.09
        vminf = 0.;
        aminf = aminf3;
        bminf = bminf3;
        cminf = cminf3;
        nppar = 3;
        chi2fit = chi2fit3;
      }
    }
 
    if (!vdrift_4parfit) {  //if not required explicitly leave the t0 and track step as at step 3
                            // just update vdrift value vmin for storing in the segments for monitoring
      aminf = aminf3;
      bminf = bminf3;
      cminf = cminf3;
      nppar = 3;
      chi2fit = chi2fit3;
    }
 
    nppar4 = nppar;
 
  }  //end nptfit >=3
 
  if (debug) {
    cout << "   dt0= 0 : slope 4  = " << bminf << " pos out = " << aminf << " chi2fitN4 = " << chi2fitN4
         << "  nppar= " << nppar4 << " T0_ev ns= " << cminf / 0.00543 << " delta v = " << vminf << endl;
    cout << nptfit << " nptfit "
         << " end  chi2fit = " << chi2fit / (nptfit - nppar) << " T0_ev ns= " << cminf / 0.00543
         << " delta v = " << vminf << endl;
  }
 
  if (fabs(vminf) >= 0.09 && debug) {  //checks only vdrift less then 10 % accepted
                                       //    cout << "vminf gt 0.09 det=  " << endl;
    //    cout << "dt0= 0 : slope 4 = "<< bminf << " pos out = " << aminf << " chi2fitN4 = " << chi2fitN4
    //   << " T0_ev ns = " << cminf/0.00543 << " delta v = "<< vminf << endl;
    //    cout << "dt0 = 0 : slope 2 = "<< b << " pos in = " << a <<" chi2fitN2 = " << chi2fitN2
    //   << " nppar = " << nppar-1 << " nptfit = " << nptfit <<endl;
    //    cout << "dt0 = 0 : slope 3 = " << bminf << " pos out = " << aminf << " chi2fitN3 = "
    //   << chi2fitN3 << " T0_ev ns = " << cminf/0.00543 << endl;
    cout << nptfit << " nptfit "
         << "   end  chi2fit = " << chi2fit << "T0_ev ns= " << cminf / 0.00543 << "delta v = " << vminf << endl;
  }
 
  if (nptfit != nppar)
    chi2fit = chi2fit / (nptfit - nppar);
}