PVPositionBuilder Class Reference

#include <RecoPixelVertexing/PixelVertexFinding/PVPositionBuilder.h>

Public Member Functions
Measurement1D	average (const reco::TrackRefVector &trks) const
	Calculate unweighted average of Z of tracks from const collection of track pointers. More...
	PVPositionBuilder ()
	Constructor does nothing, no data members. More...
Measurement1D	wtAverage (const reco::TrackRefVector &trks) const
	Calculate Error-Weighted average of Z of tracks from const collection of track pointers. More...

Detailed Description

This helper class calculates the average Z position of a collection of tracks. You have the option of calculating the straight average, or making a weighted average using the error of the Z of the tracks. This class is used by the pixel vertexing to make a PVCluster and is used by other PVCluster-related classes

Author

Aaron Dominguez (UNL)

Definition at line 17 of file PVPositionBuilder.h.

Constructor & Destructor Documentation

PVPositionBuilder()

PVPositionBuilder::PVPositionBuilder

(

)

Constructor does nothing, no data members.

Constructor does nothing since this class has no data.

Definition at line 5 of file PVPositionBuilder.cc.

{}

Member Function Documentation

average()

Measurement1D PVPositionBuilder::average

(

const reco::TrackRefVector &

trks

)

const

Calculate unweighted average of Z of tracks from const collection of track pointers.

Definition at line 7 of file PVPositionBuilder.cc.

                                                                             {
  // Cut and paste (more or less) from same class in ORCA framework
  double ntracks = double(trks.size());
  if (ntracks == 0)
    return Measurement1D(0., 0.);
  double sumZIP = 0;
  double err = 0;
  for (unsigned int i = 0; i < trks.size(); i++) {
    sumZIP += trks[i]->dz();    // Z at IP
    err += trks[i]->dzError();  // error on Z at IP (I hope). Fix d.k.
  }
  return Measurement1D(sumZIP / ntracks, err / ntracks / std::sqrt(ntracks));
}

References submitPVResolutionJobs::err, mps_fire::i, vertices_cff::ntracks, edm::RefVector< C, T, F >::size(), and mathSSE::sqrt().

wtAverage()

Measurement1D PVPositionBuilder::wtAverage

(

const reco::TrackRefVector &

trks

)

const

Calculate Error-Weighted average of Z of tracks from const collection of track pointers.

Definition at line 21 of file PVPositionBuilder.cc.

                                                                               {
  double ntracks = double(trks.size());
  if (ntracks == 0)
    return Measurement1D(0.0, 0.0);
  double sumUp = 0;
  double sumDown = 0;
  double err = 0;
  for (unsigned int i = 0; i < trks.size(); i++) {
    //    double err2 = trks[i]->covariance(3,3); // error on Z at IP (I hope)
    double err2 = trks[i]->dzError();  // Fix d.k.
    err2 *= err2;
    if (err2 != 0) {
      sumUp += trks[i]->dz() * 1 / err2;  // error-weighted average of Z at IP
      sumDown += 1 / err2;
    }
    err += std::sqrt(err2);
  }
  if (sumDown > 0)
    return Measurement1D(sumUp / sumDown, err / ntracks / sqrt(ntracks));
  else
    return Measurement1D(0.0, 0.0);
}

References submitPVResolutionJobs::err, mps_fire::i, vertices_cff::ntracks, edm::RefVector< C, T, F >::size(), and mathSSE::sqrt().