/data/refman/pasoursint/CMSSW_4_4_5_patch3/src/TrackingTools/TrajectoryState/src/FreeTrajectoryState.cc

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#include "TrackingTools/TrajectoryState/interface/FreeTrajectoryState.h"
#include "TrackingTools/AnalyticalJacobians/interface/JacobianCurvilinearToCartesian.h"
#include "TrackingTools/AnalyticalJacobians/interface/JacobianCartesianToCurvilinear.h"

#include <cmath>


void FreeTrajectoryState::missingError() {
 throw TrajectoryStateException(
      "FreeTrajectoryState: attempt to access errors when none available");
}

// implementation of non-trivial methods of FreeTrajectoryState

// Warning: these methods violate constness

// convert curvilinear errors to cartesian
void FreeTrajectoryState::createCartesianError() const{
  
  JacobianCurvilinearToCartesian curv2Cart(theGlobalParameters);
  const AlgebraicMatrix65& jac = curv2Cart.jacobian();

  theCartesianError = 
    ROOT::Math::Similarity(jac, theCurvilinearError.matrix());
  theCartesianErrorValid = true;
}

// convert cartesian errors to curvilinear
void FreeTrajectoryState::createCurvilinearError() const{
  
  JacobianCartesianToCurvilinear cart2Curv(theGlobalParameters);
  const AlgebraicMatrix56& jac = cart2Curv.jacobian();
  
  theCurvilinearError = 
    ROOT::Math::Similarity(jac, theCartesianError.matrix());
  theCurvilinearErrorValid = true;
} 


void FreeTrajectoryState::rescaleError(double factor) {
  bool zeroField = parameters().magneticFieldInInverseGeV(GlobalPoint(0,0,0)).mag2()==0;
  if unlikely(zeroField) {
    if (theCartesianErrorValid){
      if (!theCurvilinearErrorValid) createCurvilinearError();
      theCurvilinearError.zeroFieldScaling(factor*factor);
      createCartesianError();
    }else
      if (theCurvilinearErrorValid) theCurvilinearError.zeroFieldScaling(factor*factor);
  } else{
    if (theCartesianErrorValid){
      theCartesianError *= (factor*factor);
    }
    if (theCurvilinearErrorValid){
      theCurvilinearError *= (factor*factor);
    }
  }
}


// check if trajectory can reach given radius

bool FreeTrajectoryState::canReach(double radius) const {
  GlobalPoint x = position();
  GlobalVector p = momentum().unit();
  double rho = transverseCurvature()*p.perp();
  double rx = rho*x.x();
  double ry = rho*x.y();
  double rr = rho*radius;
  double ax = p.x()*rx + p.y()*ry;
  double ay = p.x()*ry - p.y()*rx + p.perp2();
  double cospsi = (.5*(rx*rx + ry*ry - rr*rr) + ay)/sqrt(ax*ax + ay*ay);
  return fabs(cospsi) <= 1.;
}