G4DormandPrinceRK78.hh

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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
 
// Author: Somnath Banerjee (CERN, Google Summer of Code 2015), 28.06.2015
// Supervision: John Apostolakis (CERN)
// --------------------------------------------------------------------
#ifndef G4DORMAND_PRINCE_RK78_HH
#define G4DORMAND_PRINCE_RK78_HH
 
#include "G4MagIntegratorStepper.hh"
 
/**
 * @brief G4DormandPrinceRK78 implements the Dormand-Prince 8(7)13M non-FSAL
 * Runge-Kutta method, a 13 stage embedded explicit Runge-Kutta method, using
 * a pair of 7th and 8th order formulae.
 */
 
class G4DormandPrinceRK78 : public G4MagIntegratorStepper
{
  public:
 
    /**
     * Constructor for G4DormandPrince745.
     *  @param[in] EqRhs Pointer to the provided equation of motion.
     *  @param[in] numberOfVariables The number of integration variables.
     *  @param[in] primary Flag for initialisation of the auxiliary stepper.
     */
    G4DormandPrinceRK78(G4EquationOfMotion* EqRhs,
                        G4int numberOfVariables = 6,
                        G4bool primary = true);
 
    /**
     * Destructor.
     */
    ~G4DormandPrinceRK78() override;
    
    /**
     * Copy constructor and assignment operator not allowed.
     */
    G4DormandPrinceRK78(const G4DormandPrinceRK78&) = delete;
    G4DormandPrinceRK78& operator=(const G4DormandPrinceRK78&) = delete;
 
    /**
     * The stepper for the Runge Kutta integration.
     * The stepsize is fixed, with the step size given by 'h'.
     * Integrates ODE starting values y[0 to 6].
     * Outputs yout[] and its estimated error yerr[].
     *  @param[in] y Starting values array of integration variables.
     *  @param[in] dydx Derivatives array.
     *  @param[in] h The given step size.
     *  @param[out] yout Integration output.
     *  @param[out] yerr The estimated error.
     */
    void Stepper( const G4double y[],
                  const G4double dydx[],
                        G4double h,
                        G4double yout[],
                        G4double yerr[]) override ;
 
    /**
     * Returns the distance from chord line.
     */
    G4double  DistChord() const override;
 
    /**
     * Returns the order, 7, of integration.
     */
    inline G4int IntegratorOrder() const override { return 7; }
 
    /**
     * Returns the stepper type-ID, "kDormandPrinceRK78".
     */
    inline G4StepperType StepperType() const override { return kDormandPrinceRK78; }
    
  private :  
    
    G4double *ak2,   *ak3,  *ak4,  *ak5,  *ak6,  *ak7, *ak8,
             *ak9,   *ak10, *ak11, *ak12, *ak13,
             *yTemp, *yIn;
 
    G4double fLastStepLength = -1.0;
 
    /** For DistChord() calculations. */
    G4double *fLastInitialVector, *fLastFinalVector,
             *fLastDyDx, *fMidVector, *fMidError;
 
    G4DormandPrinceRK78* fAuxStepper = nullptr;
};
 
#endif