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PosteriorWeightsCalculator.cc

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#include "TrackingTools/GsfTracking/interface/PosteriorWeightsCalculator.h"

#include "TrackingTools/PatternTools/interface/MeasurementExtractor.h"
#include "FWCore/MessageLogger/interface/MessageLogger.h"

#include <cfloat>

std::vector<double> PosteriorWeightsCalculator::weights(const TransientTrackingRecHit& recHit) const {
        switch (recHit.dimension()) {
                case 1: return weights<1>(recHit);
                case 2: return weights<2>(recHit);
                case 3: return weights<3>(recHit);
                case 4: return weights<4>(recHit);
                case 5: return weights<5>(recHit);
        }
        throw cms::Exception("Error: rechit of size not 1,2,3,4,5");
}

template<unsigned int D>
std::vector<double> PosteriorWeightsCalculator::weights(const TransientTrackingRecHit& recHit) const {
  typedef typename AlgebraicROOTObject<D,5>::Matrix MatD5;
  typedef typename AlgebraicROOTObject<5,D>::Matrix Mat5D;
  typedef typename AlgebraicROOTObject<D,D>::SymMatrix SMatDD;
  typedef typename AlgebraicROOTObject<D>::Vector VecD;
  
  std::vector<double> weights;
  if ( predictedComponents.empty() )  return weights;
  weights.reserve(predictedComponents.size());

  std::vector<double> detRs;
  detRs.reserve(predictedComponents.size());
  std::vector<double> chi2s;
  chi2s.reserve(predictedComponents.size());
  //
  // calculate chi2 and determinant / component and find
  //   minimum / maximum of chi2
  //  
  double chi2Min(DBL_MAX);
  for ( unsigned int i=0; i<predictedComponents.size(); i++ ) {
    MeasurementExtractor me(predictedComponents[i]);
    // Residuals of aPredictedState w.r.t. aRecHit, 
    VecD r = asSVector<D>(recHit.parameters()) - me.measuredParameters<D>(recHit);
    // and covariance matrix of residuals
    SMatDD V = asSMatrix<D>(recHit.parametersError());
    SMatDD R = V + me.measuredError<D>(recHit);
    double detR;
    if (! R.Det2(detR) ) {
      edm::LogError("PosteriorWeightsCalculator") << "PosteriorWeightsCalculator: determinant failed";
      return std::vector<double>();
    }
    detRs.push_back(detR);

    int ierr = ! R.Invert(); // if (ierr != 0) throw exception;
    if ( ierr!=0 ) {
      edm::LogError("PosteriorWeightsCalculator") 
        << "PosteriorWeightsCalculator: inversion failed, ierr = " << ierr;
      return std::vector<double>();
    }
    double chi2 = ROOT::Math::Similarity(r,R); 
    chi2s.push_back(chi2);
    if ( chi2<chi2Min )  chi2Min = chi2;
  }
  if ( detRs.size()!=predictedComponents.size() ||
       chi2s.size()!=predictedComponents.size() ) {
    edm::LogError("PosteriorWeightsCalculator") << "Problem in vector sizes";
    return std::vector<double>();
  }
  //
  // calculate weights (extracting a common factor
  //   exp(-0.5*chi2Min) to avoid numerical problems
  //   during exponentation
  //
  double sumWeights(0.);
  for ( unsigned int i=0; i<predictedComponents.size(); i++ ) {
    double priorWeight = predictedComponents[i].weight();

    double chi2 = chi2s[i] - chi2Min;

    double tempWeight(0.);
    if ( detRs[i]>FLT_MIN ) {
      //
      // Calculation of (non-normalised) weight. Common factors exp(-chi2Norm/2.) and
      // 1./sqrt(2*pi*recHit.dimension()) have been omitted
      //
      tempWeight = priorWeight * sqrt(1./detRs[i]) * exp(-0.5 * chi2); 
    }
    //      else {
    //        edm::LogInfo("PosteriorWeightsCalculator") << "PosteriorWeightsCalculator: detR < FLT_MIN !!";
    //      }
    weights.push_back(tempWeight);
    sumWeights += tempWeight;
  }
  if ( sumWeights<DBL_MIN ) {
    edm::LogInfo("PosteriorWeightsCalculator") << "PosteriorWeightsCalculator: sumWeight < DBL_MIN";
    return std::vector<double>();
  }

  if ( weights.size()!=predictedComponents.size() ) {
    edm::LogError("PosteriorWeightsCalculator") << "Problem in vector sizes (2)";
    return std::vector<double>();
  }
  for (std::vector<double>::iterator iter = weights.begin();
       iter != weights.end(); iter++) {
    (*iter) /= sumWeights;
  }

  return weights;
}

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