// ********************************************************************
// * License and Disclaimer                                           *
// *                                                                  *
// * The  Geant4 software  is  copyright of the Copyright Holders  of *
// * the Geant4 Collaboration.  It is provided  under  the terms  and *
// * conditions of the Geant4 Software License,  included in the file *
// * LICENSE and available at  http://cern.ch/geant4/license .  These *
// * include a list of copyright holders.                             *
// *                                                                  *
// * Neither the authors of this software system, nor their employing *
// * institutes,nor the agencies providing financial support for this *
// * work  make  any representation or  warranty, express or implied, *
// * regarding  this  software system or assume any liability for its *
// * use.  Please see the license in the file  LICENSE  and URL above *
// * for the full disclaimer and the limitation of liability.         *
// *                                                                  *
// * This  code  implementation is the result of  the  scientific and *
// * technical work of the GEANT4 collaboration.                      *
// * By using,  copying,  modifying or  distributing the software (or *
// * any work based  on the software)  you  agree  to acknowledge its *
// * use  in  resulting  scientific  publications,  and indicate your *
// * acceptance of all terms of the Geant4 Software license.          *
// ********************************************************************
//
//
// $Id: $
//
// Helper namespace 'magneticfield'
//
// Description:
//    An implementation of the 7 stage embedded Runge-Kutta 4,5 pair (RK547FEq2)
//    from the paper D. J. Higham and G. Hall,
//    “Embedded Runge-Kutta formulae with stable equilibrium states”,
//    J. Comput. Appl. Math., vol. 29, no. 1, pp. 25–33, Jan. 1990.
//
//    Implementation by Dmitry Sorokin - GSoC 2017
//       Work supported by Google as part of Google Summer of Code 2017.
//    Supervision / code review: John Apostolakis

#ifndef G4RK547FEq2_HH
#define G4RK547FEq2_HH

#include "G4MagIntegratorStepper.hh"
#include "G4FieldTrack.hh"

class G4RK547FEq2 : public G4MagIntegratorStepper {
public:
    G4RK547FEq2(G4EquationOfMotion* EqRhs, G4int integrationVariables = 6);

    virtual void Stepper(
        const G4double yInput[],
        const G4double dydx[],
        G4double hstep,
        G4double yOutput[],
        G4double yError[]) override;

    void Stepper(
        const G4double yInput[],
        const G4double dydx[],
        G4double hstep,
        G4double yOutput[],
        G4double yError[],
        G4double dydxOutput[]);

    G4RK547FEq2 (const G4RK547FEq2&) = delete;
    G4RK547FEq2& operator = (const G4RK547FEq2&) = delete;

    virtual G4double DistChord() const override;
    virtual G4int IntegratorOrder() const override { return 4; }

private:
    void makeStep(
        const G4double yInput[],
        const G4double dydx[],
        const G4double hstep,
        G4double yOutput[],
        G4double* dydxOutput = nullptr,
        G4double* yError = nullptr) const;

    G4double fyIn[G4FieldTrack::ncompSVEC],
             fdydx[G4FieldTrack::ncompSVEC],
             fyOut[G4FieldTrack::ncompSVEC],
             fdydxOut[G4FieldTrack::ncompSVEC];
    G4double fhstep= -1.0;
};

#endif