G4RK547FEq2.hh

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// $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