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/// \file field/BlineTracer/include/G4BlineEquation.hh
/// \brief Definition of the G4BlineEquation class
//
//
// $Id$
//
// 
// --------------------------------------------------------------------
//
// G4BlineEquation
//
// Class description:
//
// This class defines the equation of motion needed to trace magnetic
// field lines in the simulation. 

// --------------------------------------------------------------------
// Author: Laurent Desorgher (desorgher@phim.unibe.ch)
//         Created - 2003-10-06
// --------------------------------------------------------------------
#ifndef G4BlineEquation_h
#define G4BlineEquation_h 1

#include "G4Mag_EqRhs.hh"
#include "G4MagneticField.hh"

class G4BlineEquation : public G4Mag_EqRhs
{
  public:  // with description

    G4BlineEquation( G4MagneticField* MagField );
    virtual ~G4BlineEquation();
      // Constructor and destructor.

    virtual void EvaluateRhsGivenB( const G4double y[],
                            const G4double B[3],
                                  G4double dydx[] ) const;
      // Given the value of the magnetic field B, this function 
      // calculates the value of the derivative dydx.

    void SetBackwardDirectionOfIntegration(G4bool abool);  

  private:

    G4bool fBackward_direction;
    G4double fDirection;
};

#endif 
