/** CbmLitRK4TrackExtrapolator.h
 *@author A.Lebedev <alebedev@jinr.ru>
 *@since 2007
 **
 ** The class performs track extrapolation in the magnetic field by solving
 ** the equation of motion of the charged  particle in the magnetic field
 ** with the 4th order Runge-Kutta method. The transport matrix is calculated
 ** by integrating the derivatives together with "zero trajectory"
 ** with the 4th order Runge-Kutta method.
 **/

#ifndef CBMLITRK4TRACKEXTRAPOLATOR_H_
#define CBMLITRK4TRACKEXTRAPOLATOR_H_

#include "CbmLitTrackExtrapolator.h"

#include "CbmLitTrackParam.h"

#include <vector>

class CbmLitField;

class CbmLitRK4TrackExtrapolator: public CbmLitTrackExtrapolator {
public:
	/* Constructor with field
	 *@param field Magnetic field.
	 */
	CbmLitRK4TrackExtrapolator(
			CbmLitField* field);

	/* Destructor */
	virtual ~CbmLitRK4TrackExtrapolator();

	/* Inherited from CbmLitTool */
	virtual LitStatus Initialize();

	/* Inherited from CbmLitTool */
	virtual LitStatus Finalize();

	/* Inherited from CbmLitTrackExtrapolation */
	virtual LitStatus Extrapolate(
		   const CbmLitTrackParam *parIn,
		   CbmLitTrackParam *parOut,
		   myf zOut,
		   std::vector<myf>* F);

	/* Inherited from CbmLitTrackExtrapolation */
	virtual LitStatus Extrapolate(
		   CbmLitTrackParam *par,
		   myf zOut,
		   std::vector<myf>* F);

protected:
	/* Calculates output track parameters and derivatives with the 4th order Runge-Kutta method.
	 * @param xIn Input track parameters vector (x, y, tx, ty, q/p).
	 * @param zIn Input Z position [cm].
	 * @param xOut Output track parameters vector (x, y, tx, ty, q/p)
	 * @param zOut Input Z position to extrapolate to [cm].
	 * @param derivs Vector with integrated derivatives.
	 */
	void RK4Order(
		   const std::vector<myf>& xIn,
		   myf zIn,
		   std::vector<myf>& xOut,
		   myf zOut,
		   std::vector<myf>& derivs) const;

	/* TODO: add comment */
	myf CalcOut(
		myf in,
		const myf k[4]) const;

	/* Transport the covariance matrix, using formula cOut = F*cIn*Ft.
	 * @param cIn Input covariance matrix.
	 * @param F Input transport matrix.
	 * @param cOut Output covariance matrix.
	 */
	void TransportC(
		const std::vector<myf>& cIn,
		const std::vector<myf>& F,
		std::vector<myf>& cOut) const;

private:
	CbmLitField* fField; // magnetic field
};

#endif //CBMLITRK4TRACKEXTRAPOLATOR_H_