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// G4HelixMixedStepper
//
// Class description:
//
// G4HelixMixedStepper split the Method used for Integration in two:
//
// If Stepping Angle ( h / R_curve) < pi/3 : use Stepper for small step
// 
// Else use  HelixExplicitEuler Stepper
//
// Stepper for the small step is G4ClassicalRK4 by default, but
//  it possible to choose other stepper,like G4CashKarpRK45 or G4RKG3_Stepper,
//  by setting StepperNumber : new HelixMixedStepper(EqRhs,N)
//
//  N=2  G4SimpleRunge;            N=3  G4SimpleHeum;
//  N=4  G4ClassicalRK4;      
//  N=6  G4HelixImplicitEuler;     N=7  G4HelixSimpleRunge;
//  N=8  G4CashKarpRK45;           N=9  G4ExactHelixStepper;
//  N=10 G4RKG3_Stepper;           N=13 G4NystromRK4
//  N=23 BogackiShampine23         N=145 TsitourasRK45 
//  N=45 BogackiShampine45         N=745 DormandPrince745 (ie DoPri5)
//
//  For completeness also available are:
//  N=11 G4ExplicitEuler           N=12 G4ImplicitEuler;   -- Likely poor
//  N=5  G4HelixExplicitEuler (testing only)
//  For recommendations see comments in 'SetupStepper' method.
//
//  Note: Like other helix steppers, only applicable in pure magnetic field

// Created: T.Nikitina, CERN - 18.05.2007, derived from G4ExactHelicalStepper
// -------------------------------------------------------------------
#ifndef G4HELIXMIXEDSTEPPER_HH
#define G4HELIXMIXEDSTEPPER_HH

#include "G4MagHelicalStepper.hh"

class G4HelixMixedStepper: public G4MagHelicalStepper
{

  public:  

    G4HelixMixedStepper(G4Mag_EqRhs* EqRhs,
                        G4int StepperNumber = -1,
                        G4double Angle_threshold = -1.0);
   ~G4HelixMixedStepper();

    void Stepper( const G4double y[],
                  const G4double dydx[],
                        G4double h,
                        G4double yout[],
                        G4double yerr[] );
      // Step 'integration' for step size 'h'
      // If SteppingAngle= h/R_curve < pi/3 uses default RK stepper
      // else use Helix Fast Method 

    void DumbStepper( const G4double y[],
                            G4ThreeVector  Bfld,
                            G4double       h,
                            G4double       yout[]);

    G4double DistChord() const;
      // Estimate maximum distance of curved solution and chord ... 
    
  public:  // with description

    inline void SetVerbose (G4int newvalue) { fVerbose = newvalue; }
  
  public:  // without description

    void PrintCalls();
    G4MagIntegratorStepper* SetupStepper(G4Mag_EqRhs* EqRhs, G4int StepperName);

    inline void     SetAngleThreshold( G4double val ) { fAngle_threshold = val; }
    inline G4double GetAngleThreshold() { return fAngle_threshold; }
    inline G4int IntegratorOrder() const { return 4; }

  private:

      G4MagIntegratorStepper* fRK4Stepper = nullptr;
        // Mixed Integration RK4 for 'small' steps
      G4int fStepperNumber = -1;
        // Int ID of RK stepper 
   
      G4double fAngle_threshold = -1.0;
        // Threshold angle (in radians ) - above it Helical stepper is used

  private:

     G4int fVerbose = 0;

     G4int fNumCallsRK4 = 0;
     G4int fNumCallsHelix = 0;
       // Used for statistic = how many calls to different steppers
    
};

#endif