/home/bes3soft/bes3soft/Boss/7.0.2/dist/7.0.2/Reconstruction/TrkReco/TrkReco-00-08-59-patch4-slc6tag/src/TLineFitter.cxx

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//-----------------------------------------------------------------------------
// $Id: TLineFitter.cxx,v 1.8 2010/03/31 09:58:59 liucy Exp $
//-----------------------------------------------------------------------------
// Filename : TLineFitter.cc
// Section  : Tracking
// Owner    : Yoshi Iwasaki
// Email    : yoshihito.iwasaki@kek.jp
//-----------------------------------------------------------------------------
// Description : A class to fit a TTrackBase object to a line.
//               See http://bsunsrv1.kek.jp/~yiwasaki/tracking/
//-----------------------------------------------------------------------------

#include "TrkReco/TLineFitter.h"
#include "TrkReco/TTrackBase.h"
#include "TrkReco/TMLine.h"
#include "TrkReco/TMLink.h"

TLineFitter::TLineFitter(const std::string & name)
: TMFitter(name), _a(0.), _b(0.), _det(0.) {
}

TLineFitter::~TLineFitter() {
}

int
TLineFitter::fit(TTrackBase & t) const {

    //...Already fitted ?...
    if (t.fitted()) return TFitAlreadyFitted;

    //...Check # of hits...
    if (t.links().length() < 2) return TFitErrorFewHits;

    unsigned n = t.links().length();
    if (_det == 0. && n == 2) {
        double x0 = t.links()[0]->position().x();
        double y0 = t.links()[0]->position().y();
        double x1 = t.links()[1]->position().x();
        double y1 = t.links()[1]->position().y();
        if (x0 == x1) return TFitFailed;
        _a = (y0 - y1) / (x0 - x1);
        _b = - _a * x1 + y1;
    }
    else {
        double sum = (double) n;
        double sumX = 0., sumY = 0., sumX2 = 0., sumXY = 0., sumY2 = 0.;
        for (unsigned i = 0; i < n; i++) {
            const HepPoint3D & p = t.links()[i]->position();
            double x = p.x();
            double y = p.y();
            sumX  += x;
            sumY  += y;
            sumX2 += x * x;
            sumXY += x * y;
            sumY2 += y * y;
        }

        _det = sum * sumX2 - sumX * sumX;
#ifdef TRKRECO_DEBUG_DETAIL
        cout << "        TLineFitter::fit ... det=" << _det << std::endl;
#endif
        if (_det == 0.) {
            return TFitFailed;
        }
        else {
            _a = (sumXY * sum - sumX * sumY) / _det;
            _b = (sumX2 * sumY - sumX * sumXY) / _det;
        }
    }

    if (t.objectType() == Line)
        ((TMLine &) t).property(_a, _b, _det);
    fitDone(t);
    return 0;
}

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