include/Geant4/G4BogackiShampine45.hh

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0025 //
0026 // G4BogackiShampine45
0027 //
0028 // Class description:
0029 //
0030 //  An implementation of the embedded RK method from the following paper
0031 //  by P. Bogacki and L. F. Shampine:
0032 //     "An efficient Runge-Kutta (4,5) pair"
0033 //     Comput. Math. with Appl., vol. 32, no. 6, pp. 15-28, Sep. 1996.
0034 //
0035 //  An interpolation method provides the value of an intermediate
0036 //  point in a step -- if a step was sucessful.
0037 //
0038 //  This version can provide the FSAL property of the method,
0039 //  which allows the reuse of the last derivative in the next step,
0040 //  but only by using the additional method GetLastDyDx() (an alternative
0041 //  interface for simpler use of FSAL is under development).
0042
0043 // Created: Somnath Banerjee, Google Summer of Code 2015, 25 May 2015
0044 // Supervision: John Apostolakis, CERN
0045 // --------------------------------------------------------------------
0046 #ifndef BOGACKI_SHAMPINE_45_HH
0047 #define BOGACKI_SHAMPINE_45_HH
0048
0049 #include "G4MagIntegratorStepper.hh"
0050
0051 class G4BogackiShampine45 : public G4MagIntegratorStepper
0052 {
0053   public:
0054
0055     G4BogackiShampine45(G4EquationOfMotion* EqRhs,
0056                         G4int numberOfVariables = 6,
0057                         G4bool primary =  true);
0058     ~G4BogackiShampine45() override;
0059
0060     G4BogackiShampine45(const G4BogackiShampine45&) = delete;
0061     G4BogackiShampine45& operator=(const G4BogackiShampine45&) = delete;
0062
0063     void Stepper( const G4double y[],
0064                   const G4double dydx[],
0065                         G4double h,
0066                         G4double yout[],
0067                         G4double yerr[] ) override ;
0068
0069     // This Stepper provides 'dense output'. After a successful
0070     // step, it is possible to obtain an estimate of the value
0071     // of the function at an intermediate point of the interval.
0072     // This requires only two additional evaluations of the
0073     // derivative (and thus the field).
0074
0075     inline void SetupInterpolation()
0076     {
0077       SetupInterpolationHigh(); // ( yInput, dydx, Step);
0078     }
0079
0080     // For calculating the output at the tau fraction of Step
0081     //
0082     inline void Interpolate( G4double tau,
0083                              G4double yOut[] ) // Output value
0084     {
0085       InterpolateHigh( tau, yOut);
0086       // InterpolateHigh( yInput, dydx, Step, yOut, tau);
0087     }
0088
0089     void SetupInterpolationHigh();
0090
0091     // For calculating the output at the tau fraction of Step
0092     //
0093     void InterpolateHigh( G4double tau,
0094                           G4double yOut[] ) const;
0095
0096     G4double  DistChord()   const override;
0097     G4int IntegratorOrder() const override { return 4; }
0098
0099     void GetLastDydx( G4double dyDxLast[] );
0100
0101     void PrepareConstants();  // Initialise the values of the bi[][] array
0102
0103   private:
0104
0105     G4double *ak2, *ak3, *ak4, *ak5, *ak6, *ak7, *ak8,
0106              *ak9, *ak10, *ak11, *yTemp, *yIn;
0107
0108     G4double *p[6];
0109
0110     G4double fLastStepLength = -1.0;
0111     G4double *fLastInitialVector, *fLastFinalVector, *fLastDyDx,
0112              *fMidVector, *fMidError;
0113       // For DistChord calculations
0114
0115     G4BogackiShampine45* fAuxStepper = nullptr;
0116       // For chord - until interpolation is proven
0117     G4bool fPreparedInterpolation = false;
0118
0119     // Class constants
0120     static G4bool fPreparedConstants;
0121     static G4double bi[12][7];
0122 };
0123
0124 #endif