// This code implementation is the intellectual property of
// the GEANT4 collaboration.
//
// By copying, distributing or modifying the Program (or any work
// based on the Program) you indicate your acceptance of this statement,
// and all its terms.
//
// $Id: G4MagIntegratorStepper.hh,v 1.4 2000/04/27 09:14:06 gcosmo Exp $
// GEANT4 tag $Name: geant4-02-00 $
//
//
// class G4MagIntegratorStepper
//
// Class description:
//
// Abstract base class for integrator of particle's equation of motion,
// used in tracking in space dependent magnetic field

// History:
// - 15.01.97  J.Apostolakis (J.Apostolakis@cern.ch)

#ifndef G4MAGIntegratorSTEPPER
#define G4MAGIntegratorSTEPPER

#include "globals.hh"
#include "G4Mag_EqRhs.hh"

class G4MagIntegratorStepper
{
  public:  // with description

     G4MagIntegratorStepper(G4Mag_EqRhs *EqRhs, G4int num_variables);
     ~G4MagIntegratorStepper(){;}
       // Constructor and destructor. No actions.

     virtual  void  Stepper(  const G4double y[],
			      const G4double dydx[],
			      const G4double h,
				    G4double yout[],
				    G4double yerr[]  ) = 0 ;
       // The stepper for the Runge Kutta integration.
       // The stepsize is fixed, with the Step size given by h.
       // Integrates ODE starting values y[0 to 6].
       // Outputs yout[] and its estimated error yerr[].

     virtual  G4double  DistChord() const = 0; 
       // Estimate the maximum distance of a chord from the true path
       // over the segment last integrated.

     void NormaliseTangentVector( G4double vec[6] );
       // Simple utility function to (re)normalise 'unit velocity' vector.

     virtual void RightHandSide( const  double y[], double dydx[] );   
       // Utility method to supply the standard Evaluation of the
       // Right Hand side of the associated equation.

     G4int  GetNumberOfVariables();
     void   SetNumberOfVariables(G4int newNo);
       // Get/Set the number of variables that the stepper will compile over.

     virtual G4int IntegratorOrder() = 0;
       // Returns the order of the integrator
       // i.e. its error behaviour is of the order O(h^order).

     G4EquationOfMotion *GetEquationOfMotion() const; 
       // As some steppers (eg RKG3) require other methods of Eq_Rhs
       // this function allows for access to them.

  public:  // without description

#if 0
     void
     SetChargeAndMomentum( const G4double particleCharge, // in e+ units
			   const G4double MomentumXc)
       //  Supply the standard Evaluation of the Right Hand side 
       //   of the associated equation.
       {theEquation_Rhs -> SetChargeAndMomentum(particleCharge, MomentumXc);}
#endif 


  private:

     G4EquationOfMotion *fEquation_Rhs;
     G4int              fNumberOfVariables;

};

#include  "G4MagIntegratorStepper.icc"

#endif  /* G4MAGIntegratorSTEPPER */