AnalyticalErrorPropagation.h

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#ifndef AnalyticalErrorPropagation_H
#define AnalyticalErrorPropagation_H

#include "FWCore/Utilities/interface/Visibility.h"
#include "TrackingTools/AnalyticalJacobians/interface/AnalyticalCurvilinearJacobian.h"
#include "TrackingTools/TrajectoryParametrization/interface/GlobalTrajectoryParameters.h"
#include "TrackingTools/TrajectoryState/interface/FreeTrajectoryState.h"
#include "TrackingTools/TrajectoryState/interface/TrajectoryStateOnSurface.h"
#include "TrackingTools/TrajectoryState/interface/SurfaceSideDefinition.h"

class Surface;

inline
std::pair<TrajectoryStateOnSurface,double>
analyticalErrorPropagation( const FreeTrajectoryState& startingState, 
        const Surface& surface, SurfaceSideDefinition::SurfaceSide side,
        const GlobalTrajectoryParameters& destParameters, 
        const double& s) {
  if unlikely(!startingState.hasError()) 
     // return state without errors
    return std::pair<TrajectoryStateOnSurface,double>(TrajectoryStateOnSurface(destParameters,surface,side),s);

    //
    // compute jacobian
    //

    // FIXME: Compute mean B field between startingState and destParameters and pass it to analyticalJacobian
    //GlobalPoint xStart = startingState.position();
    //GlobalPoint xDest = destParameters.position();
    //GlobalVector h1  = destParameters.magneticFieldInInverseGeV(xStart);
    //GlobalVector h2  = destParameters.magneticFieldInInverseGeV(xDest);
    //GlobalVector h = 0.5*(h1+h2);
    //LogDebug("RungeKutta") << "AnalyticalErrorPropagation: The Fields are: " << h1 << ", " << h2 << ", " << h ; 
    
    // 
    AnalyticalCurvilinearJacobian analyticalJacobian(startingState.parameters(), 
                             destParameters.position(), 
                             destParameters.momentum(), s);
    auto const & jacobian = analyticalJacobian.jacobian();
    return std::pair<TrajectoryStateOnSurface,double>(
              TrajectoryStateOnSurface(destParameters,
                                        ROOT::Math::Similarity(jacobian, startingState.curvilinearError().matrix()),
                                        surface,side),
              s);
}

#endif