include/Geant4/G4TsitourasRK45.hh

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0025 //
0026 // G4TsitourasRK45
0027 //
0028 // Class description:
0029 //
0030 // Tsitouras - 5(4) RK stepper (non-FSAL version)
0031 // Implements RK tableau from 'Table 1' of:
0032 //    C. Tsitouras, "Runge-Kutta pairs of order 5(4) satisfying only
0033 //    the first column simplifying assumption"
0034 //    Computers & Mathematics with Applications,
0035 //    vol. 62, no. 2, pp. 770-775, 2011.
0036
0037 // Author: Somnath Banerjee (CERN, Google Summer of Code 2015), 11.06.2015
0038 // Supervision: John Apostolakis (CERN)
0039 // --------------------------------------------------------------------
0040 #ifndef TSITOURAS_RK45_HH
0041 #define TSITOURAS_RK45_HH
0042
0043 #include "G4MagIntegratorStepper.hh"
0044
0045 /**
0046  * @brief G4TsitourasRK45 is an implementation of the 5(4) Runge-Kutta
0047  * stepper (non-FSAL version).
0048  */
0049
0050 class G4TsitourasRK45 : public G4MagIntegratorStepper
0051 {
0052   public:
0053
0054     /**
0055      * Constructor for G4TsitourasRK45.
0056      *  @param[in] EqRhs Pointer to the provided equation of motion.
0057      *  @param[in] numberOfVariables The number of integration variables.
0058      *  @param[in] primary Flag for initialisation of the auxiliary stepper.
0059      */
0060     G4TsitourasRK45(G4EquationOfMotion* EqRhs,
0061                     G4int numberOfVariables = 6,
0062                     G4bool primary = true);
0063     /**
0064      * Destructor.
0065      */
0066     ~G4TsitourasRK45() override;
0067
0068     /**
0069      * Copy constructor and assignment operator not allowed.
0070      */
0071     G4TsitourasRK45(const G4TsitourasRK45&) = delete;
0072     G4TsitourasRK45& operator=(const G4TsitourasRK45&) = delete;
0073
0074     /**
0075      * The stepper for the Runge Kutta integration.
0076      * The stepsize is fixed, with the step size given by 'h'.
0077      * Integrates ODE starting values y[0 to 6].
0078      * Outputs yout[] and its estimated error yerr[].
0079      *  @param[in] y Starting values array of integration variables.
0080      *  @param[in] dydx Derivatives array.
0081      *  @param[in] h The given step size.
0082      *  @param[out] yout Integration output.
0083      *  @param[out] yerr The estimated error.
0084      */
0085     void Stepper( const G4double y[],
0086                   const G4double dydx[],
0087                         G4double h,
0088                         G4double yout[],
0089                         G4double yerr[] ) override;
0090
0091     /**
0092      * Setup all coefficients for interpolation.
0093      */
0094     void SetupInterpolation( /* const G4double yInput[],
0095                               const G4double dydx[],
0096                               const G4double Step */  );
0097
0098     /**
0099      * Calculates the output at the tau fraction of step.
0100      *  @param[in] yInput Starting values array of integration variables.
0101      *  @param[in] dydx Derivatives array.
0102      *  @param[in] Step The given step size.
0103      *  @param[out] yOut Interpolation output.
0104      *  @param[in] tau The tau fraction of the step.
0105      */
0106     void Interpolate( const G4double yInput[],
0107                       const G4double dydx[],
0108                       const G4double Step,
0109                             G4double yOut[],
0110                             G4double tau );
0111     void interpolate( const G4double yInput[],
0112                       const G4double dydx[],
0113                             G4double yOut[],
0114                             G4double Step,
0115                             G4double tau);
0116
0117     /**
0118      * Returns the distance from chord line.
0119      */
0120     G4double DistChord() const override;
0121
0122     /**
0123      * Returns the order, 4, of integration.
0124      */
0125     inline G4int IntegratorOrder() const override { return 4; }
0126
0127     /**
0128      * Returns the stepper type-ID, "kTsitourasRK45".
0129      */
0130     inline G4StepperType StepperType() const override { return kTsitourasRK45; }
0131
0132   private :
0133
0134     G4double *ak2, *ak3, *ak4, *ak5, *ak6, *ak7, *ak8, *yTemp, *yIn;
0135
0136     G4double fLastStepLength = 0.0;
0137     G4double *fLastInitialVector, *fLastFinalVector,
0138              *fLastDyDx, *fMidVector, *fMidError;
0139       // For DistChord calculations
0140
0141     G4TsitourasRK45* fAuxStepper = nullptr;
0142 };
0143
0144 #endif