include/Geant4/G4NystromRK4.hh

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0025 //
0026 // G4NystromRK4
0027 //
0028 // Class description:
0029 //
0030 // Integrates the equations of the motion of a particle in a magnetic field
0031 // using 4th Runge-Kutta-Nystrom method with errors estimation
0032 // (ATL-SOFT-PUB-2009-01)
0033 // Current form can be used only for 'pure' magnetic field.
0034 // Notes: 1) field must be time-independent.
0035 //        2) time is not integrated
0036
0037 // Created: I.Gavrilenko, 15.05.2009 (as G4AtlasRK4)
0038 // Adaptations: J.Apostolakis, November 2009
0039 // -------------------------------------------------------------------
0040
0041 #ifndef G4NYSTROMRK4_HH
0042 #define G4NYSTROMRK4_HH
0043
0044 #include "G4MagIntegratorStepper.hh"
0045 #include "G4Mag_EqRhs.hh"
0046 #include "G4CachedMagneticField.hh"
0047 #include "G4ThreeVector.hh"
0048
0049 #include <memory>
0050
0051 class G4NystromRK4 : public G4MagIntegratorStepper
0052 {
0053   public:
0054
0055     G4NystromRK4(G4Mag_EqRhs* EquationMotion,
0056                  G4double distanceConstField = 0.0);
0057       // Can be used only for Magnetic Fields - and for 6 variables (x,p)
0058    ~G4NystromRK4() override = default;
0059
0060     void Stepper(const G4double y[],
0061                  const G4double dydx[],
0062                        G4double hstep,
0063                        G4double yOut[],
0064                        G4double yError[]) override;
0065       // Single call for integration result and error
0066       // Provides error via analytical method
0067
0068     void SetDistanceForConstantField(G4double length);
0069     G4double GetDistanceForConstantField() const;
0070
0071     G4int IntegratorOrder() const override { return 4; }
0072     G4double DistChord() const override;
0073
0074   private:
0075
0076     inline void GetFieldValue(const G4double point[4], G4double field[3]);
0077     inline G4double GetFCof();
0078
0079     G4CachedMagneticField* GetField();
0080     const G4CachedMagneticField* GetField() const;
0081
0082     G4double fMomentum = 0.0;
0083     G4double fMomentum2 = 0.0;
0084     G4double fInverseMomentum = 0.0;
0085     G4double fCoefficient = 0.0;
0086     G4ThreeVector fInitialPoint;
0087     G4ThreeVector fMidPoint;
0088     G4ThreeVector fEndPoint;
0089
0090     std::unique_ptr<G4CachedMagneticField> fCachedField;
0091 };
0092
0093 #include "G4NystromRK4.icc"
0094
0095 #endif