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// G4DormandPrinceRK78
//
// Class description:
//
// Dormand-Prince 8(7)13M non-FSAL RK method, a 13 stage embedded
// explicit Runge-Kutta method, using a pair of 7th and 8th order formulae.
//
// Paper proposing this RK scheme:
// P.J. Prince, J.R. Dormand, "High order embedded Runge-Kutta formulae",
// Journal of Computational and Applied Mathematics, Volume 7, Issue 1, 1981,
// Pages 67-75, ISSN 0377-0427, DOI: 10.1016/0771-050X(81)90010-3

// Created: Somnath Banerjee, Google Summer of Code 2015, 28 June 2015
// Supervision: John Apostolakis, CERN
// --------------------------------------------------------------------
#ifndef G4DORMAND_PRINCE_RK78_HH
#define G4DORMAND_PRINCE_RK78_HH

#include "G4MagIntegratorStepper.hh"

class G4DormandPrinceRK78 : public G4MagIntegratorStepper
{
  public:

    G4DormandPrinceRK78(G4EquationOfMotion* EqRhs,
                        G4int numberOfVariables = 6,
                        G4bool primary = true);
    ~G4DormandPrinceRK78();
    
    G4DormandPrinceRK78(const G4DormandPrinceRK78&) = delete;
    G4DormandPrinceRK78& operator=(const G4DormandPrinceRK78&) = delete;

    void Stepper( const G4double y[],
                  const G4double dydx[],
                  G4double h,
                  G4double yout[],
                  G4double yerr[]) ;

    G4double  DistChord()   const;
    inline G4int IntegratorOrder() const { return 7; }
    
 private :  
    
    G4double *ak2,   *ak3,  *ak4,  *ak5,  *ak6,  *ak7, *ak8,
             *ak9,   *ak10, *ak11, *ak12, *ak13,
             *yTemp, *yIn;

    G4double fLastStepLength = -1.0;
    G4double *fLastInitialVector, *fLastFinalVector,
             *fLastDyDx, *fMidVector, *fMidError;
      // For DistChord calculations

    G4DormandPrinceRK78* fAuxStepper = nullptr;
};

#endif
