/afs/cern.ch/work/a/aaltunda/public/www/CMSSW_6_2_5/src/RecoPixelVertexing/PixelTriplets/plugins/ThirdHitZPrediction.cc

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#include "ThirdHitZPrediction.h"

namespace {
  template<class T> T sqr(T t) { return t * t; }
}


ThirdHitZPrediction::Range ThirdHitZPrediction::operator()(
   const GlobalPoint& thePoint3, float erroRPhi3) const
{
  double dR23 = (thePoint3-thePoint2).perp();

  double slope = dR23/dR12;
  if (    (theCurvature > 1.e-4) 
          && (std::abs(0.5*dR23*theCurvature) < 1.) 
          ) slope = std::asin(0.5*dR23*theCurvature)/dS12;

  double z3 = thePoint2.z() + dZ12*slope;

  double sqr_errorXY23 = sqr_errorXY2+sqr(erroRPhi3);
  double error = sqrt( sqr( (1+dR23/dR12)*theErrorZ2 )
                       + sqr( dR23/dR12 * theErrorZ1 )
                       + sqr(dZ12/dR12 )*sqr_errorXY23 
                       + sqr((dZ12/dR12)*(dR23/dR12))*sqr_errorXY12
                       );
  error *= theNSigma;
  return Range(z3-error,z3+error);
}