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// G4HelixSimpleRunge
//
// Class description:
//
// Helix Simple Runge-Kutta stepper for magnetic field:
//       x_1 = x_0 + h * ( dx( t_0+h/2, x_0 + h/2 * dx( t_0, x_0) ) )
//
// Second order solver.
// Take the derivative at a position to be assumed at the middle of the
// Step and add it to the current position.

// Author: W.Wander (MIT), 03.12.1998
// -------------------------------------------------------------------
#ifndef G4HELIXSIMPLERUNGE_HH
#define G4HELIXSIMPLERUNGE_HH

#include "G4MagHelicalStepper.hh"

/**
 * @brief G4HelixSimpleRunge implements a simple Helix stepper for magnetic
 * field with 2nd order solver.
 */

class G4HelixSimpleRunge : public G4MagHelicalStepper
{
  public:

    /**
     * Constructor for G4HelixSimpleRunge.
     *  @param[in] EqRhs Pointer to the provided equation of motion.
     */
    G4HelixSimpleRunge(G4Mag_EqRhs* EqRhs);

    /**
     * Default Destructor.
     */
    ~G4HelixSimpleRunge() override = default;
  
    /**
     * The stepper function for the integration.
     *  @param[in] y Starting values array of integration variables.
     *  @param[in] Bfld The field vector.
     *  @param[in] h The given step size.
     *  @param[out] yout Integration output.
     */
    void  DumbStepper( const G4double y[],
                             G4ThreeVector Bfld,
                             G4double h,
                             G4double yout[] ) override;

    /**
     * Returns the order, 2, of integration.
     */
    inline G4int IntegratorOrder() const override { return 2; }

    /**
     * Returns the stepper type-ID, "kHelixSimpleRunge".
     */
    inline G4StepperType StepperType() const override { return kHelixSimpleRunge; }
};

#endif