G4BogackiShampine23.hh

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// G4BogackiShampine23
//
// Class description:
//
//  Bogacki-Shampine - 4 - 3(2) non-FSAL implementation 
//
//  An implementation of the embedded RK method from the paper 
//  [1] P. Bogacki and L. F. Shampine,
//     "A 3(2) pair of Runge - Kutta formulas"
//     Appl. Math. Lett., vol. 2, no. 4, pp. 321-325, Jan. 1989.
//
//  This version does not utilise the FSAL property of the method,
//  which would allow the reuse of the last derivative in the next step.
//  (Alternative FSAL implementation created with revised interface)

// Created: Somnath Banerjee, Google Summer of Code 2015, 20 May 2015
// Supervision: John Apostolakis, CERN
// --------------------------------------------------------------------
#ifndef G4BOGACKI_SHAMPINE23_HH
#define G4BOGACKI_SHAMPINE23_HH

#include "G4MagIntegratorStepper.hh"
#include "G4FieldTrack.hh"

class G4BogackiShampine23 : public G4MagIntegratorStepper
{
  public:

    G4BogackiShampine23(G4EquationOfMotion* EqRhs,
                        G4int numberOfVariables = 6);

    virtual void Stepper(const G4double yInput[],
                         const G4double dydx[],
                         G4double hstep,
                         G4double yOutput[],
                         G4double yError[]) override;

    void Stepper(const G4double yInput[],
                 const G4double dydx[],
                 G4double hstep,
                 G4double yOutput[],
                 G4double yError[],
                 G4double dydxOutput[]);

    G4BogackiShampine23(const G4BogackiShampine23&) = delete;
    G4BogackiShampine23& operator = (const G4BogackiShampine23&) = delete;

    virtual G4double DistChord() const override;
    virtual G4int IntegratorOrder() const  override { return 3; }

  private:

    void makeStep(const G4double yInput[],
                  const G4double dydx[],
                  const G4double hstep,
                  G4double yOutput[],
                  G4double* dydxOutput = nullptr,
                  G4double* yError = nullptr) const;

    G4double fyIn[G4FieldTrack::ncompSVEC],
             fdydx[G4FieldTrack::ncompSVEC],
             fyOut[G4FieldTrack::ncompSVEC],
             fdydxOut[G4FieldTrack::ncompSVEC];
    G4double fhstep = -1.0;
};

#endif