G4TSimpleRunge.hh

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// G4TSimpleRunge
//
// Class description:
//
// Templated version of G4SimpleRunge
//
//
// Created: Josh Xie  (supported by Google Summer of Code 2014 )
// Supervisors:  Sandro Wenzel, John Apostolakis (CERN)
// Adapted from G4G4TSimpleRunge class
// --------------------------------------------------------------------
#ifndef G4TSimpleRunge_HH
#define G4TSimpleRunge_HH
 
#include <cassert>
#include "G4TMagErrorStepper.hh"
#include "G4ThreeVector.hh"
 
template <class T_Equation, int N>
class G4TSimpleRunge
  : public G4TMagErrorStepper<G4TSimpleRunge<T_Equation, N>, T_Equation, N>
{
 public:  // with description
  static constexpr double IntegratorCorrection = 1. / ((1 << 2) - 1);
 
  G4TSimpleRunge(T_Equation* EqRhs, G4int numberOfVariables = 6)
    : G4TMagErrorStepper<G4TSimpleRunge<T_Equation, N>, T_Equation, N>(
        EqRhs, numberOfVariables)
    , fNumberOfVariables(numberOfVariables)
    , fEquation_Rhs(EqRhs)
      
  {
    // default GetNumberOfStateVariables() == 12
    assert(this->GetNumberOfStateVariables() <= 12);
  }
 
  ~G4TSimpleRunge() { ; }
 
  inline void RightHandSide(G4double y[],
                            G4double dydx[])
  {
    fEquation_Rhs->T_Equation::RightHandSide(y, dydx);
  }
 
  inline void DumbStepper(const G4double yIn[],
                          const G4double dydx[],
                          G4double h, G4double yOut[]) // override final
  {
    // Initialise time to t0, needed when it is not updated by the integration.
    yTemp[7] = yOut[7] = yIn[7];  //  Better to set it to NaN;  // TODO
 
    for(G4int i = 0; i < N; ++i)
    {
      yTemp[i] = yIn[i] + 0.5 * h * dydx[i];
    }
 
    this->RightHandSide(yTemp, dydxTemp);
 
    for(G4int i = 0; i < N; ++i)
    {
      yOut[i] = yIn[i] + h * (dydxTemp[i]);
    }
  }
 
 public:  // without description
  inline G4int IntegratorOrder() const { return 2; }
 
 private:
  G4int fNumberOfVariables;
  G4double dydxTemp[N > 12 ? N : 12];
  G4double yTemp[N > 12 ? N : 12];
 
  T_Equation* fEquation_Rhs;
  // scratch space
};
 
#endif /* G4TSimpleRunge_HH */