/afs/cern.ch/work/a/aaltunda/public/www/CMSSW_5_3_14/src/RecoVertex/VertexTools/src/VertexDistanceXY.cc

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#include "RecoVertex/VertexTools/interface/VertexDistanceXY.h"
#include "DataFormats/GeometryVector/interface/GlobalVector.h"
#include "RecoVertex/VertexPrimitives/interface/VertexState.h"
#include "FWCore/Utilities/interface/Exception.h"
#include <cfloat>


using namespace reco;

Measurement1D
VertexDistanceXY::signedDistance(const Vertex& vtx1, const Vertex & vtx2,
                                         const GlobalVector & momentum) const
{
  Measurement1D unsignedDistance = distance(vtx1, vtx2);
  Basic3DVector<float> diff = Basic3DVector<float> (vtx2.position()) - 
    Basic3DVector<float> (vtx1.position());
  if ((momentum.x()*diff.x() + momentum.y()*diff.y()) < 0 )
    return Measurement1D(-1.0*unsignedDistance.value(),unsignedDistance.error());
  return unsignedDistance;
}



Measurement1D 
VertexDistanceXY::distance(const GlobalPoint & vtx1Position, 
                           const GlobalError & vtx1PositionError, 
                           const GlobalPoint & vtx2Position, 
                           const GlobalError & vtx2PositionError) const
{
    AlgebraicSymMatrix33 error = vtx1PositionError.matrix()
      + vtx2PositionError.matrix();
    GlobalVector diff = vtx1Position - vtx2Position;
    AlgebraicVector3 vDiff;
    vDiff[0] = diff.x();
    vDiff[1] = diff.y();
    vDiff[2] = 0.;
    
    double dist=sqrt(pow(diff.x(),2)+pow(diff.y(),2));
    
    double err2 =  ROOT::Math::Similarity(error,vDiff);
    double err  = 0;
    if( dist != 0) err = sqrt(err2)/dist;
       
    return Measurement1D(dist,err);
}


float 
VertexDistanceXY::compatibility(const GlobalPoint & vtx1Position, 
                                const GlobalError & vtx1PositionError, 
                                const GlobalPoint & vtx2Position, 
                                const GlobalError & vtx2PositionError) const
{
  // error matrix of residuals
  AlgebraicSymMatrix33 err1 = vtx1PositionError.matrix();
  AlgebraicSymMatrix33 err2 = vtx2PositionError.matrix();
  AlgebraicSymMatrix22 error; 
  error[0][0] = err1[0][0] + err2[0][0];
  error[0][1] = err1[0][1] + err2[0][1];
  error[1][1] = err1[1][1] + err2[1][1];
  if (error == theNullMatrix) return FLT_MAX;

  // position residuals
  GlobalVector diff = vtx2Position - vtx1Position;
  AlgebraicVector2 vDiff;
  vDiff[0] = diff.x();
  vDiff[1] = diff.y();

  // Invert error matrix of residuals
  bool ifail = !error.Invert();
  if (ifail) {
    throw cms::Exception("VertexDistanceXY::matrix inversion problem");
  }

  return ROOT::Math::Similarity(error,vDiff);
}