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

Date:

2007/03/12 00:50:36

Revision:

1.4

Author

Aaron Dominguez (UNL)

Definition at line 19 of file PVPositionBuilder.h.

Constructor & Destructor Documentation

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

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.

References i, edm::RefVector< C, T, F >::size(), and mathSSE::sqrt().

Referenced by DivisiveVertexFinder::findVertexes().

                                                                             {
  // 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) );

}

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.

References i, edm::RefVector< C, T, F >::size(), and mathSSE::sqrt().

Referenced by DivisiveVertexFinder::findVertexes().

                                                                               {
  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 );
}