AnalyticalCurvilinearJacobian.h

#ifndef AnalyticalCurvilinearJacobian_H
#define AnalyticalCurvilinearJacobian_H

#include "DataFormats/Math/interface/AlgebraicROOTObjects.h"
#include "DataFormats/GeometryVector/interface/GlobalPoint.h"
#include "DataFormats/GeometryVector/interface/GlobalVector.h"

/** \class AnalyticalCurvilinearJacobian 
 * Creating Jacobian of transformation within the curvilinear frame.
 * The basic functionality of this class is to provide the (analytical) Jacobian matrix
 * of the transformation within the curvilinear frame from the state defined
 * by globalParameters to the state defined by x and p. This Jacobian can then be used
 * to yield the corresponding error propagation. The current implementation
 * is based on the original derivations by W. Wittek. However, due to the implicit float
 * precision, two terms ((4,1) and (5,1)) have been modified in order to make the 
 * calculations more stable in a numerical sense.
 */

class GlobalTrajectoryParameters;

class AnalyticalCurvilinearJacobian {
public:
  /// default constructor (for tests)
  AnalyticalCurvilinearJacobian() : theJacobian(ROOT::Math::SMatrixNoInit()) {}

  /// get Field at starting state (internally)
  AnalyticalCurvilinearJacobian(const GlobalTrajectoryParameters& globalParameters,
                                const GlobalPoint& x,
                                const GlobalVector& p,
                                const double& s);
  /// new: give Field as a parameter
  AnalyticalCurvilinearJacobian(const GlobalTrajectoryParameters& globalParameters,
                                const GlobalPoint& x,
                                const GlobalVector& p,
                                const GlobalVector& theFieldInInverseGeV,
                                const double& s);

public:
  /// result for non-vanishing curvature
  void computeFullJacobian(
      const GlobalTrajectoryParameters&, const GlobalPoint&, const GlobalVector&, const GlobalVector&, const double& s);
  /// result for non-vanishing curvature and "small" step
  void computeInfinitesimalJacobian(
      const GlobalTrajectoryParameters&, const GlobalPoint&, const GlobalVector&, const GlobalVector&, const double& s);
  /// straight line approximation
  void computeStraightLineJacobian(const GlobalTrajectoryParameters&,
                                   const GlobalPoint&,
                                   const GlobalVector&,
                                   const double& s);

  const AlgebraicMatrix55& jacobian() const { return theJacobian; }

private:
  AlgebraicMatrix55 theJacobian;
};

#endif