ParameterResolutions.cxx

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#include "AtlfastAlgs/ParameterResolutions.h"
#include <cmath>

namespace Atlfast 
{

  double ParameterResolutions::resolution( const TrackTrajectory& traj ) const
  {
    // resolutions are given by c0(eta) + c1(eta)/sqrt(pT) + c2(eta)/pT + c3(eta)/pT/sqrt(pT) + c4(eta)/pT^2
    // have to interpolate eta between bin edges for coefficients
    TrackParameters track = traj.parameters();
    double eta = std::abs( track.eta() );
    double pT  = track.pT();

    std::vector<BinID>::const_iterator iter = m_coefficientBins.begin();
    std::vector<BinID>::const_iterator end  = m_coefficientBins.end();
    std::vector<double> coefficients;
    for ( ; iter != end; ++iter ) 
    {
      double value = this->interpolate( eta, iter->low(), iter->high() );
      coefficients.push_back(value);
    }
    return calculateResolution( pT, coefficients );
  }

  
  double ParameterResolutions::interpolate( double eta, double coeffLow, double coeffHigh ) const 
  {
    double slope = ( coeffHigh - coeffLow ) / ( m_etaHigh - m_etaLow );
    double value = coeffLow + slope * ( eta - m_etaLow );
    return value;
  }
  
  double ParameterResolutions::calculateResolution( double pT, const std::vector<double>& coefficients ) const
  {
    if ( pT == 0 ) return 0;
    double resolution = 0;
    std::vector<double>::const_iterator powerSeries = m_powerSeries.begin();
    std::vector<double>::const_iterator iter = coefficients.begin();
    std::vector<double>::const_iterator end  = coefficients.end();
    
    for ( ; iter != end; ++iter )
    {
        resolution += (*iter) / std::pow( pT, (*powerSeries) ); 
        ++powerSeries;
    }   
    return resolution;
  }

}

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