QratCscClusterFitter.cxx

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/*
  Copyright (C) 2002-2025 CERN for the benefit of the ATLAS collaboration
*/
 
#include "QratCscClusterFitter.h"
 
#include <iomanip>
#include <sstream>
 
#include "EventPrimitives/EventPrimitives.h"
#include "EventPrimitives/EventPrimitivesHelpers.h"
#include "MuonPrepRawData/CscClusterStatus.h"
#include "MuonPrepRawData/CscPrepData.h"
#include "MuonPrepRawData/CscStripPrepData.h"
#include "MuonReadoutGeometry/CscReadoutElement.h"
#include "TrkEventPrimitives/LocalDirection.h"
#include "TrkEventPrimitives/ParamDefs.h"
#include "CxxUtils/trapping_fp.h"
 
using Muon::CscClusterStatus;
using Muon::CscPrepData;
using Muon::CscStripPrepData;
using MuonGM::CscReadoutElement;
 
using DataNames = ICscClusterFitter::DataNames;
using Result = ICscClusterFitter::Result;
using Results = std::vector<Result>;
 
enum CscStation { UNKNOWN_STATION, CSS, CSL };
enum CscPlane { CSS_ETA, CSL_ETA, CSS_PHI, CSL_PHI, UNKNOWN_PLANE };
 
namespace {
    std::string splane(CscPlane plane) {
        switch (plane) {
            case CSS_ETA: return "CSS eta";
            case CSL_ETA: return "CSL eta";
            case CSS_PHI: return "CSS phi";
            case CSL_PHI: return "CSL phi";
            case UNKNOWN_PLANE: return "no such plane";
        }
        return "no such plane";
    }
 
    CscPlane findPlane(int station, bool measphi) {
        if (station == 1) {
            if (measphi)
                return CSS_PHI;
            else
                return CSS_ETA;
        } else if (station == 2) {
            if (measphi)
                return CSL_PHI;
            else
                return CSL_ETA;
        }
        return UNKNOWN_PLANE;
    }
}  // namespace
 
//******************************************************************************
 
int qrat_correction(CscPlane plane, double qrat, double& cor, double& dcordqrat) {
    std::vector<double> pfac;
    if (plane == CSS_ETA) {
        if (qrat < 0.095) return 1;
        if (qrat > 1.01) return 1;
        if (qrat < 0.15) {
            pfac.push_back(-5.483);
            pfac.push_back(130.6);
            pfac.push_back(-1296.);
            pfac.push_back(5994.);
            pfac.push_back(-10580.);
        } else if (qrat < 0.30) {
            pfac.push_back(-0.9225);
            pfac.push_back(5.569);
            pfac.push_back(2.908);
            pfac.push_back(-66.19);
            pfac.push_back(108.5);
        } else {
            pfac.push_back(-0.4246);
            pfac.push_back(2.619);
            pfac.push_back(-3.642);
            pfac.push_back(2.837);
            pfac.push_back(-0.8916);
        }
    } else if (plane == CSL_ETA) {
        if (qrat < 0.105) return 1;
        if (qrat > 1.01) return 1;
        if (qrat < 0.25) {
            pfac.push_back(-2.823);
            pfac.push_back(42.71);
            pfac.push_back(-279.1);
            pfac.push_back(879.2);
            pfac.push_back(-1062.);
        } else {
            pfac.push_back(-0.5409);
            pfac.push_back(3.110);
            pfac.push_back(-4.630);
            pfac.push_back(3.800);
            pfac.push_back(-1.241);
        }
    } else {
        return 3;
    }
    cor = 0.0;
    dcordqrat = 0.0;
    double term = 1.0;
    for (unsigned int ipow = 0; ipow < pfac.size(); ++ipow) {
        dcordqrat += ipow * pfac[ipow] * term;
        if (ipow) term *= qrat;
        cor += pfac[ipow] * term;
    }
    return 0;
}
 
//******************************************************************************
 
// Calculate QRAT correction by interpolation.
// Input array runs from 0.0 to 1.0.
// Output is shifted by 0.5.
// The value in each bin corresponds to upper edge of the bin.
//   qrmin = min value of the qrat distribution
//   corvals = array of corrections
//   qrat = input value of qrat
//   cor = output correction
//   dcordqrat = derivative of cor w.r.t. qrat
 
int qrat_interpolation(double qrmin, const std::vector<double>& corvals, double qrat, double& cor, double& dcordqrat) {
    int nbin = corvals.size();
    if (!nbin) return 1;
    // Treat any QRAT below the minimum as if it were at the minumum.
    if (qrat < qrmin) qrat = qrmin;
    // Find the bin holding dqrat.
    double dqrat = 1.0 / nbin;
    int bin = int(qrat / dqrat);
    // Extract the value for this bin (x1) and the preceding (x0)
    // and the following (x2).
    double x1 = corvals[bin];
    if (x1 == 0.0) return 2;
    double x0 = bin == 0 ? 0.0 : corvals[bin - 1];
    double x2 = bin == nbin - 1 ? 1.0 : corvals[bin + 1];
    // Assign the qrat values for these bins. If this is the first
    // bin with data, then use the input qrmin.
    double qrat0 = dqrat * bin;
    double qrat1 = qrat0 + dqrat;
 
    if (x0 == 0.0) {
        if (qrmin > qrat0 && qrmin < qrat1) { qrat0 = qrmin; }
    }
    // Calculate correction and derivative.
    // Use quadratic interpolation with the high edge of this bin,
    // the preceding and the following. For the last bin, use linear
    // interpolation.
    if (bin == nbin - 1) {
        double a = x0;
        double b = (x1 - x0) / dqrat;
        cor = a + b * (qrat - qrat0);
        dcordqrat = b;
    } else {
        double d0 = qrat1 - qrat0;
        double d = dqrat;
        double w = 1.0 / (d0 * d * d + d0 * d0 * d);
        double a = x1;
        double b = w * d * d * (x1 - x0) + w * d0 * d0 * (x2 - x1);
        double c = w * d0 * (x2 - x1) - w * d * (x1 - x0);
        cor = a + b * (qrat - qrat1) + c * (qrat - qrat1) * (qrat - qrat1);
        dcordqrat = b + 2.0 * c * (qrat - qrat1);
    }
    if (cor < 0.0) cor = 0.0;
    // Shift correction to center of bin.
    cor -= 0.50;
    return 0;
}
 
//****************************************************************************

int qrat_atanh(const double a, const double b, double c, const double x0, double qrat, double& cor, double& dcordqrat) {
    if (qrat <= 0) return 1;  // avoid trouble in error calculation
    // minimum qrat value (at pos=-1) or use pos = -0.5?
    double qrmin = a + b * tanh(c * (-1 - x0));
 
    // Treat any QRAT below the minimum as if it were at the minumum.
    if (qrat < qrmin) qrat = qrmin;
    double z = (qrat - a) / b;
    cor = atanh(z) / c + x0;
    dcordqrat = 1.0 / (1.0 - z * z) / b / c;
 
    return 0;
}
 
//****************************************************************************
 
QratCscClusterFitter::QratCscClusterFitter(const std::string& type, const std::string& aname, const IInterface* parent) :
    AthAlgTool(type, aname, parent) {
    declareInterface<ICscClusterFitter>(this);
    m_max_width.push_back(5);                   // CSS eta
    m_max_width.push_back(5);                   // CSL eta
    m_max_width.push_back(3);                   // CSS phi
    m_max_width.push_back(2);                   // CSL phi
    declareProperty("max_width", m_max_width);  // Maximum width (strips) for unspoiled clusters
    declareProperty("position_option_eta", m_posopt_eta = "ATANH");
    declareProperty("position_option_phi", m_posopt_phi = "NONE");
    declareProperty("error_option_eta", m_erropt_eta = "CHARGE");
    declareProperty("error_option_phi", m_erropt_phi = "NONE");
    declareProperty("error_eta", m_error_eta = 0.050);  // in mm this is for fixed error
    declareProperty("error_phi", m_error_phi = 0.140);  // in mm this is for fixed error
 
    declareProperty("precisionErrorScaler", m_precisionErrorScaler = 1.0);  // in mm this is for fixed error
 
    declareProperty("qrat_maxdiff", m_qrat_maxdiff = 0.15);                   // in strips
    declareProperty("qrat_maxsig", m_qrat_maxsig = 6.0);                      // in strips
    declareProperty("error_tantheta", m_error_tantheta = 0.57);               // in mm
    declareProperty("xtan_css_eta_offset", m_xtan_css_eta_offset = 0.0015);   // in mm
    declareProperty("xtan_css_eta_slope", m_xtan_css_eta_slope = 0.000137);   // in mm
    declareProperty("xtan_csl_eta_offset", m_xtan_csl_eta_offset = -0.0045);  // in mm
    declareProperty("xtan_csl_eta_slope", m_xtan_csl_eta_slope = 0.000131);   // in mm
    declareProperty("qratmin_css_eta", m_qratmin_css_eta = 0.0940459);
    declareProperty("qratmin_csl_eta", m_qratmin_csl_eta = 0.108975);
    declareProperty("qratcor_css_eta", m_qratcor_css_eta);  // in strips
    declareProperty("qratcor_csl_eta", m_qratcor_csl_eta);  // in strips
 
    declareProperty("atanh_a_css_eta", m_atanh_a_css_eta = 1.5);
    declareProperty("atanh_b_css_eta", m_atanh_b_css_eta = 1.411);
    declareProperty("atanh_c_css_eta", m_atanh_c_css_eta = 2.329);
    declareProperty("atanh_x0_css_eta", m_atanh_x0_css_eta = 0.6601);
    declareProperty("atanh_a_csl_eta", m_atanh_a_csl_eta = 1.516);
    declareProperty("atanh_b_csl_eta", m_atanh_b_csl_eta = 1.427);
    declareProperty("atanh_c_csl_eta", m_atanh_c_csl_eta = 2.35);
    declareProperty("atanh_x0_csl_eta", m_atanh_x0_csl_eta = 0.6615);
 
    declareProperty("dposmin", m_dposmin = 0.082);
}
 
//**********************************************************************
 
StatusCode QratCscClusterFitter::initialize() {
    ATH_MSG_VERBOSE("Initalizing " << name());
 
    // retrieve MuonDetectorManager from the conditions store
    ATH_CHECK(m_DetectorManagerKey.initialize());
 
    ATH_CHECK(m_idHelperSvc.retrieve());
 
    if (m_alignmentTool.retrieve().isFailure()) {
        ATH_MSG_WARNING(name() << ": unable to retrieve cluster fitter " << m_alignmentTool);
    } else {
        ATH_MSG_DEBUG(name() << ": retrieved " << m_alignmentTool);
    }
 
    ATH_MSG_DEBUG("Properties for " << name() << ":");
    ATH_MSG_DEBUG("       Eta position option: " << m_posopt_eta);
    ATH_MSG_DEBUG("       Phi position option: " << m_posopt_phi);
    ATH_MSG_DEBUG("          Eta error option: " << m_erropt_eta);
    ATH_MSG_DEBUG("          Phi error option: " << m_erropt_phi);
    ATH_MSG_DEBUG("        Eta assigned error: " << m_error_eta);
    ATH_MSG_DEBUG("        Phi assigned error: " << m_error_phi);
    ATH_MSG_DEBUG("        Max strip pos diff: " << m_qrat_maxdiff);
    ATH_MSG_DEBUG("         Max strip pos sig: " << m_qrat_maxsig);
    ATH_MSG_DEBUG("    Non-normal error coeff: " << m_error_tantheta);
    ATH_MSG_DEBUG("  CSS eta pos-slope offset: " << m_xtan_css_eta_offset);
    ATH_MSG_DEBUG("   CSS eta pos-slope slope: " << m_xtan_css_eta_slope);
    ATH_MSG_DEBUG("  CSL eta pos-slope offset: " << m_xtan_csl_eta_offset);
    ATH_MSG_DEBUG("   CSL eta pos-slope slope: " << m_xtan_csl_eta_slope);
    ATH_MSG_DEBUG("      CSS eta table offset: " << m_qratmin_css_eta);
    ATH_MSG_DEBUG("      CSL eta table offset: " << m_qratmin_csl_eta);
    ATH_MSG_DEBUG("        CSS eta table size: " << m_qratcor_css_eta.size());
    ATH_MSG_DEBUG("        CSL eta table size: " << m_qratcor_csl_eta.size());
 
    ATH_MSG_DEBUG("atanh_a_css_eta:            " << m_atanh_a_css_eta);
    ATH_MSG_DEBUG("atanh_b_css_eta:            " << m_atanh_b_css_eta);
    ATH_MSG_DEBUG("atanh_c_css_eta:            " << m_atanh_c_css_eta);
    ATH_MSG_DEBUG("atanh_x0_css_eta:           " << m_atanh_x0_css_eta);
    ATH_MSG_DEBUG("atanh_a_csl_eta:            " << m_atanh_a_csl_eta);
    ATH_MSG_DEBUG("atanh_b_csl_eta:            " << m_atanh_b_csl_eta);
    ATH_MSG_DEBUG("atanh_c_csl_eta:            " << m_atanh_c_csl_eta);
    ATH_MSG_DEBUG("atanh_x0_csl_eta:           " << m_atanh_x0_csl_eta);
 
    ATH_MSG_DEBUG("Minimum pos error:          " << m_dposmin);
 
    return StatusCode::SUCCESS;
}
 
//**********************************************************************
 
const DataNames& QratCscClusterFitter::dataNames() const {
    auto init = [&]() {
        DataNames dnames;
        bool dofixed = false;
        bool docharge = false;
        if (m_posopt_phi == "POLYNOMIAL" || m_posopt_phi == "TABLE" || m_posopt_phi == "ATANH") {
            if (m_erropt_phi == "FIXED") dofixed = true;
            if (m_erropt_phi == "CHARGE") docharge = true;
        }
        if (m_posopt_eta == "POLYNOMIAL" || m_posopt_eta == "TABLE" || m_posopt_eta == "ATANH") {
            if (m_erropt_eta == "FIXED") dofixed = true;
            if (m_erropt_eta == "CHARGE") docharge = true;
        }
        if (dofixed || docharge) {
            dnames.emplace_back("scor1");
            dnames.emplace_back("scor2");
            dnames.emplace_back("scor");
        }
        if (docharge) {
            dnames.emplace_back("dscor1");
            dnames.emplace_back("dscor2");
            dnames.emplace_back("dscor");
            dnames.emplace_back("scordiff");
            dnames.emplace_back("dscordiff");
        }
        return dnames;
    };
    static const DataNames dnames = init();
    return dnames;
}
 
//**********************************************************************
 
Results QratCscClusterFitter::fit(const StripFitList& sfits, double tantheta) const {
    ATH_MSG_VERBOSE("QRAT fit with tool " << name());
 
    Results results;
 
    // Check input has at least three strips.
    unsigned int nstrip = sfits.size();
    if (nstrip < 3) {
        ATH_MSG_VERBOSE("  Input has fewer than three strips.");
        if (nstrip == 2) {
            Muon::CscTimeStatus tstatus = (sfits[0].charge > sfits[1].charge) ? sfits[0].timeStatus : sfits[1].timeStatus;
            results.emplace_back(1, Muon::CscStatusNarrow, tstatus);
        } else if (nstrip == 1) {
            Muon::CscTimeStatus tstatus = sfits[0].timeStatus;
            results.emplace_back(1, Muon::CscStatusNarrow, tstatus);
        }
        return results;
    }
 
    // Fetch the number of strips and check the input arrays.
    for (unsigned int istrip = 0; istrip < nstrip; ++istrip) {
        if (sfits[istrip].strip == nullptr) {
            ATH_MSG_WARNING("Strip pointer is null.");
            results.emplace_back(2);
            return results;
        }
    }
 
    // Use the first strip to extract the layer parameters.
    const CscStripPrepData* pstrip = sfits[0].strip;
    Identifier idStrip0 = pstrip->identify();
 
    // retrieve MuonDetectorManager from the conditions store
    SG::ReadCondHandle<MuonGM::MuonDetectorManager> DetectorManagerHandle{m_DetectorManagerKey};
    const MuonGM::MuonDetectorManager* MuonDetMgr = DetectorManagerHandle.cptr();
    if (MuonDetMgr == nullptr) {
        ATH_MSG_ERROR("Null pointer to the MuonDetectorManager conditions object");
        return results;
    }
    const CscReadoutElement* pro = MuonDetMgr->getCscReadoutElement(idStrip0);
 
    bool measphi = m_idHelperSvc->cscIdHelper().CscIdHelper::measuresPhi(idStrip0);
    double pitch = pro->cathodeReadoutPitch(0, measphi);
    unsigned int maxstrip = pro->maxNumberOfStrips(measphi);
    unsigned int strip0 = m_idHelperSvc->cscIdHelper().strip(idStrip0) - 1;
    int station = m_idHelperSvc->cscIdHelper().stationName(idStrip0) - 49;  // 1=CSS, 2=CSL
 
    CscPlane plane = findPlane(station, measphi);
    if (plane == UNKNOWN_PLANE) {
        ATH_MSG_WARNING("Invalid CSC plane: station=" << station << "; measphi=" << measphi);
        results.emplace_back(3);
        return results;
    }
 
    // Display input strips.
    ATH_MSG_VERBOSE("QRAT fittter input has " << nstrip << " strips");
    for (unsigned int istrip = 0; istrip < nstrip; ++istrip) {
        Identifier id = sfits[istrip].strip->identify();
        ATH_MSG_VERBOSE("  " << station << " : " << measphi << "  " << m_idHelperSvc->cscIdHelper().wireLayer(id) << "  " << istrip << " "
                             << m_idHelperSvc->cscIdHelper().strip(id) << " " << sfits[istrip].charge);
    }
 
    // Find the peak strip and check the shape.
    unsigned int istrip_peak = 0;  // strip number within cluster
    // Loop over strips excluding the edges.
    for (unsigned int istrip = 1; istrip < nstrip - 1; ++istrip) {
        // Tell clang to optimize assuming that FP operations may trap.
        CXXUTILS_TRAPPING_FP;
        StripFit sfit = sfits[istrip];
        float qthis = sfit.charge;
        float qlast = sfits[istrip - 1].charge;
        float qnext = sfits[istrip + 1].charge;
        // Peak if the adjacent strips have less charge.
        bool ispeak = qthis > qlast && qthis > qnext;
        // Special case: next strip has the same charge.
        // Require the previous strip has less charge and the next following
        // strip be absent or have less charge.
        if (!ispeak) {
            if (qthis == qnext) { ispeak = (qthis > qlast) && (istrip + 2 == nstrip || sfits[istrip + 2].charge < qthis); }
        }
        // Special case: first and second strips have the same charge.
        // Require the third strip has less charge.
        if (!ispeak) {
            if (istrip == 1) {
                if (qthis == qlast) {
                    ispeak = qthis > qnext;  // bug found 10/13/07
                }
            }
        }
        // Record if peak.
        if (ispeak) {
            if (istrip_peak) {                                           // Error if multiple peaks are found.
                results.emplace_back(6, Muon::CscStatusMultiPeak);  // Time status should be defined in SimpleClusterFit...
                return results;
            }
            istrip_peak = istrip;
        }
    }
    ATH_MSG_VERBOSE("  Peak is at " << istrip_peak << "th strip in cluster");
 
    // Check we are not on the edge.
    if (strip0 <= 0 || strip0 + nstrip > maxstrip) {
        results.emplace_back(4, Muon::CscStatusEdge, sfits[istrip_peak].timeStatus);
        return results;
    }
 
    // MS: remove this check since width is amplitude dependent.
    // use saturation check instead
    /**************************************
    if ( nstrip > m_max_width[plane] ) {
      //  if ( nstrip_threshold > m_max_width[plane] ) {
      results.push_back(Result(5, Muon::CscStatusWide, sfits[istrip_peak].timeStatus));
      return results;
    }
    ***************************************/
 
    // Cluster is spoiled if peak is not at the center.
    bool is_even = 2 * (nstrip / 2) == nstrip;
    bool atcenter = istrip_peak == nstrip / 2 || (is_even && istrip_peak + 1 == nstrip / 2);
    if (!atcenter) {
        results.emplace_back(7, Muon::CscStatusSkewed, sfits[istrip_peak].timeStatus);
        return results;
    }
 
    if (sfits[istrip_peak].stripStatus == Muon::CscStrStatSaturated || sfits[istrip_peak - 1].stripStatus == Muon::CscStrStatSaturated ||
        sfits[istrip_peak + 1].stripStatus == Muon::CscStrStatSaturated) {
        results.emplace_back(15, Muon::CscStatusSaturated, sfits[istrip_peak].timeStatus);
        return results;
    }
 
    // left/peak/right strip should have good time information....
    if (sfits[istrip_peak].stripStatus != Muon::CscStrStatSuccess
        //       || sfits[istrip_peak-1].stripStatus != Muon::CscStrStatSuccess
        //       || sfits[istrip_peak+1].stripStatus != Muon::CscStrStatSuccess ) {
    ) {
        results.emplace_back(14, Muon::CscStatusStripFitFailed, sfits[istrip_peak].timeStatus);
        return results;
    } else if (sfits[istrip_peak - 1].stripStatus == Muon::CscStrStatHot || sfits[istrip_peak - 1].stripStatus == Muon::CscStrStatDead ||
               sfits[istrip_peak + 1].stripStatus == Muon::CscStrStatHot || sfits[istrip_peak + 1].stripStatus == Muon::CscStrStatDead) {
        results.emplace_back(14, Muon::CscStatusStripFitFailed, sfits[istrip_peak].timeStatus);
        return results;
    }

    // Set initial strip position.
    double savg = istrip_peak;
 
    // Calculate QRAT correction to strip position.
    std::string posopt = m_posopt_eta;
    std::string erropt = m_erropt_eta;
    double dpos = 0.0;
    if (measphi) {
        posopt = m_posopt_phi;
        erropt = m_erropt_phi;
    }
    double q1 = sfits[istrip_peak - 1].charge;
    double q0 = sfits[istrip_peak].charge;
    double q2 = sfits[istrip_peak + 1].charge;
    double qrat1 = q1 / q0;
    double qrat2 = q2 / q0;
    double dq1 = sfits[istrip_peak - 1].dcharge;
    double dq0 = sfits[istrip_peak].dcharge;
    double dq2 = sfits[istrip_peak + 1].dcharge;
 
    ATH_MSG_VERBOSE("  QRAT charge ratios: " << qrat1 << " " << qrat2);
    double scor1 = 0.;  // left side correction.
    double dscordqrat1 = 0.;
    double scor2 = 0;  // right side correction.
    double dscordqrat2 = 0.;
    int stat1 = 0;
    int stat2 = 0;
    if (posopt == "POLYNOMIAL") {
        stat1 = qrat_correction(plane, qrat1, scor1, dscordqrat1);
        stat2 = qrat_correction(plane, qrat2, scor2, dscordqrat2);
    } else if (posopt == "TABLE") {
        double qrmin = 0.0;
        const std::vector<double>* pcor = nullptr;
        if (plane == CSS_ETA) {
            qrmin = m_qratmin_css_eta;
            pcor = &m_qratcor_css_eta;
        } else if (plane == CSL_ETA) {
            qrmin = m_qratmin_csl_eta;
            pcor = &m_qratcor_csl_eta;
        } else {
            ATH_MSG_WARNING("    Invalid QRAT plane: " << splane(plane));
            results.emplace_back(8);
            return results;
        }
        if (pcor) {
            stat1 = qrat_interpolation(qrmin, *pcor, qrat1, scor1, dscordqrat1);
            stat2 = qrat_interpolation(qrmin, *pcor, qrat2, scor2, dscordqrat2);
        } else {
            stat1 = 99;
        }
    } else if (posopt == "ATANH") {  // MS: atanh parametrization
        double a, b, c, x0;          // parameters
        if (plane == CSS_ETA) {
            a = m_atanh_a_css_eta;
            b = m_atanh_b_css_eta;
            c = m_atanh_c_css_eta;
            x0 = m_atanh_x0_css_eta;
        } else if (plane == CSL_ETA) {
            a = m_atanh_a_csl_eta;
            b = m_atanh_b_csl_eta;
            c = m_atanh_c_csl_eta;
            x0 = m_atanh_x0_csl_eta;
        } else {
            ATH_MSG_WARNING("    Invalid QRAT plane: " << splane(plane));
            results.emplace_back(8);
            return results;
        }
        stat1 = qrat_atanh(a, b, c, x0, qrat1, scor1, dscordqrat1);
        stat2 = qrat_atanh(a, b, c, x0, qrat2, scor2, dscordqrat2);
 
    } else {
        ATH_MSG_WARNING("    Invalid position option: " << posopt);
        results.emplace_back(9);
        return results;
    }
    if (stat1 || stat2) {
        ATH_MSG_VERBOSE("    QRAT correction failed: SPOILED");
        results.emplace_back(10);
        return results;
    }
    ATH_MSG_VERBOSE("  QRAT strip corrs: " << scor1 << " " << scor2);
    ATH_MSG_VERBOSE("  QRAT derivatives: " << dscordqrat1 << " " << dscordqrat2);
 
    // Compare left and right.
    // Flip sign of the left side correction.
    scor1 = -scor1;
    dscordqrat1 = -dscordqrat1;
    double scor = 0.0;
    DataMap dmap;
    // Calculation weighting corrections by their derivatives, i.e. assuming the
    // two charge ratios have the same error.
    if (erropt == "FIXED") {
        double w1 = 1 / (dscordqrat1 * dscordqrat1);
        double w2 = 1 / (dscordqrat2 * dscordqrat2);
        scor = (w1 * scor1 + w2 * scor2) / (w1 + w2);
        double scor_diff = std::abs(scor2 - scor1);
        ATH_MSG_VERBOSE("  Combined corr: " << scor);
        dpos = measphi ? m_error_phi : m_error_eta;
        // Fill data map.
        dmap["scor1"] = scor1;
        dmap["scor2"] = scor2;
        dmap["scor"] = scor;
        // Exit if measurements are inconsistent.
        if (scor_diff > m_qrat_maxdiff) {
            ATH_MSG_VERBOSE("  SPOILED (scor_diff=" << scor_diff << ")");
            results.emplace_back(11, Muon::CscStatusQratInconsistent);
            return results;
        }
        // Calculation using the (independent) errors in the three charges.
    } else if (erropt == "CHARGE") {
        // Calculate intermediate variables.
        double x1 = dscordqrat1 * qrat1;
        double x2 = dscordqrat2 * qrat2;
        double dqq0 = dq0 / q0;
        double dqq1 = dq1 / q1;
        double dqq2 = dq2 / q2;
        double rnum = (-x1 * x1 * dqq1 * dqq1 + x2 * x2 * dqq2 * dqq2 + (x2 * x2 - x1 * x1) * dqq0 * dqq0);
        double rden = (x1 * x1 * dqq1 * dqq1 + x2 * x2 * dqq2 * dqq2 + (x2 - x1) * (x2 - x1) * dqq0 * dqq0);
        double rfac = rnum / rden;
        // Calculate the significance of the difference between the measurements.
        double dscor_diff = sqrt(rden);
        double scor_diff = scor2 - scor1;
        double scor_sig = std::abs(scor_diff) / dscor_diff;
        // Calculate the weighted average of the corrections.
        double w1 = 0.5 * (1.0 + rfac);
        double w2 = 0.5 * (1.0 - rfac);
        scor = w1 * scor1 + w2 * scor2;
        // Calculate the error in this average.
        double ddscor1 = w1 * x1 * dqq1;
        double ddscor2 = w2 * x2 * dqq2;
        double ddscor0 = (w1 * x1 + w2 * x2) * dqq0;
        double dscor = sqrt(ddscor1 * ddscor1 + ddscor2 * ddscor2 + ddscor0 * ddscor0);
        dpos = pitch * dscor;
        // add minimum error (in mm) in quadrature:
        dpos = sqrt(dpos * dpos + m_dposmin * m_dposmin);
        // Fill data map.
        double dscor1 = std::abs(x1) * sqrt(dqq1 * dqq1 + dqq0 * dqq0);
        double dscor2 = std::abs(x2) * sqrt(dqq2 * dqq2 + dqq0 * dqq0);
        dmap["scor1"] = scor1;
        dmap["dscor1"] = dscor1;
        dmap["scor2"] = scor2;
        dmap["dscor2"] = dscor2;
        dmap["scordiff"] = scor_diff;
        dmap["dscordiff"] = dscor_diff;
        dmap["scor"] = scor;
        dmap["dscor"] = dscor;
        // Debugging.
        ATH_MSG_VERBOSE("QRAT CHARGE calculation");
        ATH_MSG_VERBOSE("       q1, q0, q2: " << q1 << " " << q0 << " " << q2);
        ATH_MSG_VERBOSE("    dq1, dq0, dq2: " << dq1 << " " << dq0 << " " << dq2);
        ATH_MSG_VERBOSE("  dscordqrat1, x1: " << dscordqrat1 << " " << x1);
        ATH_MSG_VERBOSE("  dscordqrat2, x2: " << dscordqrat2 << " " << x2);
        ATH_MSG_VERBOSE("     scor1 = " << scor1 << " +/- " << dscor1);
        ATH_MSG_VERBOSE("     scor2 = " << scor2 << " +/- " << dscor2);
        ATH_MSG_VERBOSE("      scor = " << scor << " +/- " << dscor);
        ATH_MSG_VERBOSE("  scordiff = " << scor_diff << " +/- " << dscor_diff);
        ATH_MSG_VERBOSE("  scor_sig = " << scor_sig);
 
        // Exit if measurements are inconsistent.
        if (scor_sig > m_qrat_maxsig) {
            ATH_MSG_VERBOSE("  SPOILED (scor_sig=" << scor_sig << ")");
            results.emplace_back(12, Muon::CscStatusQratInconsistent, sfits[istrip_peak].timeStatus);
            return results;
        }
    } else {
        ATH_MSG_WARNING("    Invalid error option: " << erropt);
        results.emplace_back(13, Muon::CscStatusUndefined, sfits[istrip_peak].timeStatus);
        return results;
    }
 
    // Correct strip position.
    savg += scor + strip0;
    ATH_MSG_VERBOSE("    QRAT corr " << splane(plane) << " nstrip=" << nstrip << " savg=" << savg << " qrat1=" << qrat1
                                     << " qrat2=" << qrat2 << " scor1=" << scor1 << " scor2=" << scor2);
 
    // Error due to incident angle.
    double dpostht = m_error_tantheta * std::abs(tantheta);
 
    // Scale error on dpos
    dpos = dpos * m_precisionErrorScaler;
 
    // Set return values.
    Result res(0, Muon::CscStatusUnspoiled);
    res.strip = istrip_peak;
    res.position = pitch * (savg + 0.5 - 0.5 * maxstrip);
 
    // internal alignment ...
    Identifier id = sfits[res.strip].strip->identify();
    double offset = m_alignmentTool->getAlignmentOffset(id);
    res.position -= offset;
 
    res.dposition = sqrt(dpos * dpos + dpostht * dpostht);
 
    res.fstrip = 0;
    res.lstrip = nstrip - 1;
    res.time = sfits[istrip_peak].time;
    res.time_beforeT0Corr = sfits[istrip_peak].time_beforeT0Corr;
    res.time_beforeBPCorr = sfits[istrip_peak].time_beforeBPCorr;
    res.timeStatus = sfits[istrip_peak].timeStatus;
 
    res.qleft = q1;
    res.qpeak = q0;
    res.qright = q2;
 
    //  res.diff = dmap["scordiff"];
    //  res.sig  = dmap["scordiff"]/dmap["dscordiff"];
 
    // cluster charge should be qsum over three strip... 3/21/2011
    res.charge = res.qleft + res.qpeak + res.qright;
    res.charge_beforeBPCorr =
        sfits[istrip_peak].charge_beforeBPCorr + sfits[istrip_peak - 1].charge_beforeBPCorr + sfits[istrip_peak + 1].charge_beforeBPCorr;
 
    res.dataMap = dmap;
 
    ATH_MSG_VERBOSE("   Position :: pos=" << res.position << " dpos:dtht=" << dpos << ":" << dpostht << " ==>" << res.dposition
                                          << "  at tanth=" << tantheta);
 
    results.push_back(res);
    return results;
}
// int QratCscClusterFitter::
// fit(const StripList&, const StripFitList& sfits,
//    double& pos, double& dpos, Muon::CscClusterStatus& clustatus,
//    unsigned int& /*istrip*/, double& /*charge*/, double& /*time*/, DataMap* /*pdmap*/) const { return 0;}
//**********************************************************************
 
double QratCscClusterFitter::getCorrectedError(const CscPrepData* pclu, double slope) const {
    // Cluster position.
    Trk::ParamDefs icor = Trk::loc1;
    Trk::ParamDefs ierr = Trk::loc1;
    double pos = pclu->localPosition()[icor];
    double dpos = Amg::error(pclu->localCovariance(), ierr);
 
    Identifier idStrip0 = pclu->identify();
    int station = m_idHelperSvc->cscIdHelper().stationName(idStrip0) - 49;  // 1=CSS, 2=CSL
    // Calculate the angle of incidence.
    double tantht = 0.0;
    if (station == 1) {
        tantht = m_xtan_css_eta_offset + m_xtan_css_eta_slope * pos;
    } else {
        tantht = m_xtan_csl_eta_offset + m_xtan_csl_eta_slope * pos;
    }
    // Correct the error using this angle.
    double old_dpostht = m_error_tantheta * std::abs(tantht);
 
    double new_dpostht = m_error_tantheta * std::abs(slope);
 
    double newError = sqrt(dpos * dpos - old_dpostht * old_dpostht + new_dpostht * new_dpostht);
 
    ATH_MSG_VERBOSE("   Position :: pos=" << pos << " dpos:newdpos=" << dpos << " : " << newError << "  " << old_dpostht << "  "
                                          << new_dpostht);
 
    if (slope < -990) { newError = sqrt(dpos * dpos + old_dpostht * old_dpostht); }
 
    return newError;
}
 
//**********************************************************************
 
Results QratCscClusterFitter::fit(const StripFitList& sfits) const {
    Results results = fit(sfits, 0.0);
    Results new_results;
    for (unsigned int iresult = 0; iresult < results.size(); ++iresult) {
        Result res = results[iresult];
        if (res.fitStatus) {
            new_results.push_back(res);
            continue;
        }
        // Fetch the chamber type.
        const CscStripPrepData* pstrip = sfits[0].strip;
        Identifier idStrip0 = pstrip->identify();
        int station = m_idHelperSvc->cscIdHelper().stationName(idStrip0) - 49;  // 1=CSS, 2=CSL
        // Calculate the angle of incidence.
        double tantht = 0.0;
        double pos = res.position;
        if (station == 1) {
            tantht = m_xtan_css_eta_offset + m_xtan_css_eta_slope * pos;
        } else {
            tantht = m_xtan_csl_eta_offset + m_xtan_csl_eta_slope * pos;
        }
        // Correct the error using this angle.
        double dpostht = m_error_tantheta * std::abs(tantht);
        double dpos = res.dposition;
 
        res.dposition = sqrt(dpos * dpos + dpostht * dpostht);
 
        // Return the updated result.
        new_results.push_back(res);
    }
 
    return new_results;
}