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// G4ExplicitEuler
//
// Class description:
//
// Explicit Euler stepper for magnetic field: x_1 = x_0 + h * dx_0.
// The most simple approach for solving linear differential equations.
// Take the current derivative and add it to the current position.

// Author: W.Wander (MIT), 12.09.1997
// -------------------------------------------------------------------
#ifndef G4EXPLICITEULER_HH
#define G4EXPLICITEULER_HH

#include "G4MagErrorStepper.hh"

/**
 * @brief G4ExplicitEuler implements an Explicit Euler stepper for magnetic
 * field: x_1 = x_0 + h * dx_0. The most simple approach for solving linear
 * differential equations. Takes the current derivative and adds it to the
 * current position.
 */

class G4ExplicitEuler : public G4MagErrorStepper
{
  public:

    /**
     * Constructor for G4ExplicitEuler.
     *  @param[in] EqRhs Pointer to the provided equation of motion.
     *  @param[in] numberOfVariables The number of integration variables.
     */
    G4ExplicitEuler(G4EquationOfMotion* EqRhs,
                    G4int numberOfVariables = 6) ;

    /**
     * Default Destructor.
     */
    ~G4ExplicitEuler() override = default;

    /**
     * The stepper function for the integration.
     *  @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.
     */
    void DumbStepper( const G4double y[],
                       const G4double dydx[],
                             G4double h,
                             G4double yout[] ) override;

    /**
     * Returns the order, 1, of integration.
     */
    inline G4int IntegratorOrder() const override { return 1; }

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

#endif