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// $Id: G4EquationOfMotion.hh,v 1.7 2002/06/11 08:38:56 japost Exp $
// GEANT4 tag $Name: geant4-05-01 $
//
//
// class G4EquationOfMotion
//
// Class description:
//
// Abstract Base Class for the right hand size of the equation of
// motion of a particle in a field.

// History:
// - Created. J.Apostolakis

#ifndef G4_EquationOfMotion_DEF
#define G4_EquationOfMotion_DEF

#include  "globals.hh"
#include  "G4Field.hh"

class G4EquationOfMotion 
{
  public:  // with description

     G4EquationOfMotion( G4Field *Field );
     virtual ~G4EquationOfMotion();
       // Constructor and virtual destructor. No operations.

     virtual void EvaluateRhsGivenB( const  G4double y[],
			             const  G4double B[3],
				     G4double dydx[] ) const = 0;
       // Given the value of the  field "B", this function 
       // calculates the value of the derivative dydx.
       // --------------------------------------------------------
       // This is the _only_ function a subclass must define.
       // The other two functions use Rhs_givenB.

     virtual void SetChargeMomentumMass(G4double particleCharge, // in e+ units
                                        G4double MomentumXc,
                                        G4double MassXc2) = 0;
       // Set the charge, momentum and mass of the current particle
       // --> used to set the equation's coefficients ...

     inline
     void RightHandSide( const  G4double y[],
				G4double dydx[] ) const;
       // This calculates the value of the derivative dydx at y.
       // It is the usual enquiry function.
       // ---------------------------
       // (It is not virtual, but calls the virtual function above.)

     void EvaluateRhsReturnB( const  G4double y[],
			      G4double dydx[],
			      G4double Field[]  ) const;
       // Same as RHS above, but also returns the value of B.
       // Should be made the new default ? after putting dydx & B in a class.

     void GetFieldValue( const  G4double Point[4],
			        G4double Field[] )  const;
       // Obtain only the field - the stepper assumes it is pure Magnetic.
       // Not protected, because G4RKG3_Stepper uses it directly.

     const G4Field* GetFieldObj() const;
     void           SetFieldObj(G4Field* pField);

  private:
     // static const int G4maximum_number_of_field_components = 16;
     enum { G4maximum_number_of_field_components = 16 } ;

     G4Field *itsField;

};

#include "G4EquationOfMotion.icc"

#endif /* G4_EquationOfMotion_DEF */