include/Geant4/G4TSimpleHeum.hh

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0025 //
0026 // G4TSimpleHeum
0027 //
0028 // Class description:
0029 //
0030 // Templated version of G4SimpleHeum.
0031 // Adapted from G4G4TSimpleHeum class.
0032 // Original desription:
0033 //
0034 // Simple Heum stepper for magnetic field:
0035 //        x_1 = x_0  +
0036 //              h * 1/4 * dx(t0,x0)  +
0037 //                  3/4 * dx(t0+2/3*h, x0+2/3*h*(dx(t0+h/3,x0+h/3*dx(t0,x0))))
0038 //
0039 // Third order solver.
0040
0041 // Author: Josh Xie (CERN, Google Summer of Code 2014), June 2014
0042 // Supervisors:  Sandro Wenzel, John Apostolakis (CERN)
0043 // --------------------------------------------------------------------
0044 #ifndef G4TSIMPLEHEUM_HH
0045 #define G4TSIMPLEHEUM_HH
0046
0047 #include <cassert>
0048 #include "G4TMagErrorStepper.hh"
0049 #include "G4ThreeVector.hh"
0050
0051 /**
0052  * @brief G4TSimpleHeum is a templated version of G4SimpleHeum.
0053  */
0054
0055 template <class T_Equation, unsigned int N>
0056 class G4TSimpleHeum
0057   : public G4TMagErrorStepper<G4TSimpleHeum<T_Equation, N>, T_Equation, N>
0058 {
0059   public:
0060
0061     constexpr static unsigned int gIntegratorOrder = 3;
0062     static constexpr double IntegratorCorrection= 1.0 / ((1<<gIntegratorOrder) - 1);
0063
0064     G4TSimpleHeum(T_Equation* EqRhs, unsigned int numberOfVariables = 6);
0065
0066     ~G4TSimpleHeum() = default;
0067
0068     inline void RightHandSide(G4double y[],
0069                               G4double dydx[])
0070     {
0071       fEquation_Rhs->T_Equation::RightHandSide(y, dydx);
0072     }
0073
0074     inline void DumbStepper(const G4double yIn[],
0075                             const G4double dydx[],
0076                             G4double h, G4double yOut[]); // override final
0077
0078     inline G4int IntegratorOrder() const { return gIntegratorOrder; }
0079
0080   private:
0081
0082     G4int fNumberOfVariables;
0083
0084     G4double dydxTemp[N];
0085     G4double dydxTemp2[N];
0086     G4double yTemp[N];
0087     G4double yTemp2[N];
0088     // scratch space
0089
0090     T_Equation* fEquation_Rhs;
0091 };
0092
0093 template <class T_Equation, unsigned int N >
0094 G4TSimpleHeum<T_Equation,N>::G4TSimpleHeum(T_Equation* EqRhs,
0095                 unsigned int numberOfVariables )
0096     : G4TMagErrorStepper<G4TSimpleHeum<T_Equation, N>, T_Equation, N>(
0097         EqRhs, numberOfVariables)
0098     , fNumberOfVariables(numberOfVariables)
0099     , fEquation_Rhs(EqRhs)
0100 {
0101   assert(fNumberOfVariables == N);
0102   if( dynamic_cast<G4EquationOfMotion*>(EqRhs) == nullptr )
0103   {
0104     G4Exception("G4TSimpleHeum: constructor", "GeomField0001",
0105                 FatalException, "Equation is not an G4EquationOfMotion.");
0106   }
0107 }
0108
0109 template <class T_Equation, unsigned int N >
0110 inline void
0111 G4TSimpleHeum<T_Equation,N>::DumbStepper(const G4double yIn[],
0112                                          const G4double dydx[],
0113                                          G4double h, G4double yOut[])
0114 {
0115   for(unsigned int i = 0; i < N; ++i)
0116   {
0117      yTemp[i] = yIn[i] + (1.0 / 3.0) * h * dydx[i];
0118   }
0119
0120   this->RightHandSide(yTemp, dydxTemp);
0121
0122   for(unsigned int i = 0; i < N; ++i)
0123   {
0124      yTemp2[i] = yIn[i] + (2.0 / 3.0) * h * dydxTemp[i];
0125   }
0126
0127   this->RightHandSide(yTemp2, dydxTemp2);
0128
0129   for(unsigned int i = 0; i < N; ++i)
0130   {
0131      yOut[i] = yIn[i] + h * (0.25 * dydx[i] + 0.75 * dydxTemp2[i]);
0132   }
0133
0134   if(fNumberOfVariables == 12)
0135   {
0136      this->NormalisePolarizationVector(yOut);
0137   }
0138 }
0139
0140 #endif