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//
// G4ErrorMag_UsualEqRhs
//
// Class description:
//
// Serves to reverse the magnetic field when propagation is backwards
// for error propagation.

// Author: Pedro Arce (CIEMAT), September 2004.
// --------------------------------------------------------------------
#ifndef G4ERRORMAG_USUALEQRHS_HH
#define G4ERRORMAG_USUALEQRHS_HH

#include "G4Mag_UsualEqRhs.hh"
#include "G4MagneticField.hh"

/**
 * @brief G4ErrorMag_UsualEqRhs serves to reverse the magnetic field when
 * propagation is backwards. It is used for error propagation.
 */

class G4ErrorMag_UsualEqRhs : public G4Mag_UsualEqRhs
{
  public:

    /**
     * Constructor for G4ErrorMag_UsualEqRhs.
     *  @param[in] MagField Pointer to the magnetic field.
     */
    G4ErrorMag_UsualEqRhs( G4MagneticField* MagField );

    /**
     * Default Destructor.
     */
    ~G4ErrorMag_UsualEqRhs() override = default;

    /**
     * Calculates the value of the derivative, given the value of the
     * magnetic field. Reverses dedx if propagation is backwards.
     *  @param[in] y Coefficients array.
     *  @param[in] B Field value.
     *  @param[out] dydx Derivatives array.
     */
    void EvaluateRhsGivenB( const G4double y[],
                            const G4double B[3],
                                  G4double dydx[] ) const override;
};

#endif