G4BogackiShampine45.hh

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// G4BogackiShampine45
//
// Class description:
//
//  An implementation of the embedded RK method from the following paper 
//  by P. Bogacki and L. F. Shampine:
//     "An efficient Runge-Kutta (4,5) pair"
//     Comput. Math. with Appl., vol. 32, no. 6, pp. 15-28, Sep. 1996.
//
//  An interpolation method provides the value of an intermediate
//  point in a step -- if a step was sucessful.
//
//  This version can provide the FSAL property of the method,
//  which allows the reuse of the last derivative in the next step,
//  but only by using the additional method GetLastDyDx() (an alternative
//  interface for simpler use of FSAL is under development).
 
// Created: Somnath Banerjee, Google Summer of Code 2015, 25 May 2015
// Supervision: John Apostolakis, CERN
// --------------------------------------------------------------------
#ifndef BOGACKI_SHAMPINE_45_HH
#define BOGACKI_SHAMPINE_45_HH
 
#include "G4MagIntegratorStepper.hh"
 
class G4BogackiShampine45 : public G4MagIntegratorStepper
{
  public:
 
    G4BogackiShampine45(G4EquationOfMotion* EqRhs,
                        G4int numberOfVariables = 6,
                        G4bool primary =  true);
    ~G4BogackiShampine45() override;
    
    G4BogackiShampine45(const G4BogackiShampine45&) = delete;
    G4BogackiShampine45& operator=(const G4BogackiShampine45&) = delete;
 
    void Stepper( const G4double y[],
                  const G4double dydx[],
                        G4double h,
                        G4double yout[],
                        G4double yerr[] ) override ;
 
    // This Stepper provides 'dense output'. After a successful
    // step, it is possible to obtain an estimate of the value
    // of the function at an intermediate point of the interval.
    // This requires only two additional evaluations of the
    // derivative (and thus the field).
 
    inline void SetupInterpolation()
    {
      SetupInterpolationHigh(); // ( yInput, dydx, Step);
    }
    
    // For calculating the output at the tau fraction of Step
    //
    inline void Interpolate( G4double tau, 
                             G4double yOut[] ) // Output value
    {
      InterpolateHigh( tau, yOut);       
      // InterpolateHigh( yInput, dydx, Step, yOut, tau);
    }
    
    void SetupInterpolationHigh();
    
    // For calculating the output at the tau fraction of Step
    //
    void InterpolateHigh( G4double tau,
                          G4double yOut[] ) const;
    
    G4double  DistChord()   const override;
    G4int IntegratorOrder() const override { return 4; }
 
    void GetLastDydx( G4double dyDxLast[] );
 
    void PrepareConstants();  // Initialise the values of the bi[][] array
   
  private:
    
    G4double *ak2, *ak3, *ak4, *ak5, *ak6, *ak7, *ak8,
             *ak9, *ak10, *ak11, *yTemp, *yIn;
 
    G4double *p[6];
 
    G4double fLastStepLength = -1.0;
    G4double *fLastInitialVector, *fLastFinalVector, *fLastDyDx,
             *fMidVector, *fMidError;
      // For DistChord calculations
    
    G4BogackiShampine45* fAuxStepper = nullptr;
      // For chord - until interpolation is proven
    G4bool fPreparedInterpolation = false;
 
    // Class constants
    static G4bool fPreparedConstants;   
    static G4double bi[12][7];
};
 
#endif