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// $Id: G4ExactHelixStepper.hh,v 1.5 2007/05/18 12:50:31 tnikitin Exp $ 
// GEANT4 tag $Name: geant4-09-03 $
//
//
// class G4ExactHelixStepper
//       -------------------
// Class description:
//
// Concrete class for particle motion in constant magnetic field.

// History:
// - 28.Jan.05  J.Apostolakis   Creation of new concrete class
// --------------------------------------------------------------------

#ifndef G4ExactHelixStepper_hh
#define G4ExactHelixStepper_hh

#include "G4Types.hh"
#include "G4ThreeVector.hh"

#include "G4MagIntegratorStepper.hh"
#include "G4MagHelicalStepper.hh"
#include "G4Mag_EqRhs.hh"

class G4ExactHelixStepper : public G4MagHelicalStepper
{
  public:  // with description

    G4ExactHelixStepper(G4Mag_EqRhs *EqRhs);
    ~G4ExactHelixStepper();
  
    void Stepper( const G4double y[],
                  const G4double dydx[],
                        G4double h,
                        G4double yout[],
                        G4double yerr[]  );
      // Step 'integration' for step size 'h'
      // Provides helix starting at y[0 to 6]
      // Outputs yout[] and ZERO estimated error yerr[]=0.
  
    void DumbStepper( const G4double y[],
                            G4ThreeVector   Bfld,
                            G4double  h,
                            G4double yout[] );
      // Performs a 'dump' Step without error calculation.
  
    G4double DistChord() const;
      // Estimate maximum distance of curved solution and chord ... 

    virtual G4int IntegratorOrder() const;

  private:

    G4ExactHelixStepper(const G4ExactHelixStepper&);
    G4ExactHelixStepper& operator=(const G4ExactHelixStepper&);
      // Private copy constructor and assignment operator.
   
  private:
    G4ThreeVector    fBfieldValue;   //  Initial value of field at last step
    G4ThreeVector    yInitialEHS,  yFinalEHS;  
    G4ThreeVector    pInitial;
    G4double         fLastStepSize;  // Length of last step
    G4double         fYInSav[7];     // Starting state of  x, p, ...
     // Values saved for calculating mid-point for chord

     G4Mag_EqRhs*  fPtrMagEqOfMot;
};



#endif  /* G4ExactHelixStepper_hh */
