include/Geant4/G4TExplicitEuler.hh

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0025 //
0026 // G4TExplicitEuler
0027 //
0028 // Class description:
0029 //
0030 // Templated version of G4ExplicitEuler.
0031 // Adapted from G4G4TExplicitEuler class.
0032 //
0033 // Information from G4Explicit Euler:
0034 // ----------------------------------
0035 // Explicit Euler stepper for magnetic field: x_1 = x_0 + h * dx_0.
0036 // The simplistic approach to solving linear differential equations.
0037 // Take the current derivative and add it to the current position.
0038
0039 // Author: Josh Xie (CERN, Google Summer of Code 2014), June 2014
0040 // Supervisors:  Sandro Wenzel, John Apostolakis (CERN)
0041 // --------------------------------------------------------------------
0042 #ifndef G4TExplicitEuler_HH
0043 #define G4TExplicitEuler_HH
0044
0045 #include "G4TMagErrorStepper.hh"
0046 #include "G4ThreeVector.hh"
0047
0048 /**
0049  * @brief G4TExplicitEuler is a templated version of G4ExplicitEuler stepper.
0050  */
0051
0052 template <class T_Equation, int N>
0053 class G4TExplicitEuler
0054   : public G4TMagErrorStepper<G4TExplicitEuler<T_Equation, N>, T_Equation, N>
0055 {
0056   public:
0057
0058     static constexpr double IntegratorCorrection = 1.;
0059
0060     G4TExplicitEuler(T_Equation* EqRhs, G4int numberOfVariables = N)
0061       : G4TMagErrorStepper<G4TExplicitEuler<T_Equation, N>, T_Equation, N>
0062                            (EqRhs, numberOfVariables), fEquation_Rhs(EqRhs)
0063     {
0064       if( numberOfVariables != N )
0065       {
0066         G4ExceptionDescription msg;
0067         msg << "Equation has an incompatible number of variables." ;
0068         msg << "   template N = " << N << " equation-Nvar= "
0069             << numberOfVariables;
0070         G4Exception("G4TExplicitEuler: constructor", "GeomField0003",
0071                     FatalErrorInArgument, msg );
0072       }
0073     }
0074
0075     ~G4TExplicitEuler() = default;
0076
0077     inline void DumbStepper(const G4double yIn[],
0078                             const G4double dydx[],
0079                             G4double h, G4double yOut[]) // override final
0080     {
0081       // Initialise time to t0, needed when it is not updated by the integration.
0082       // yOut[7] = yIn[7];   //  Better to set it to NaN;  // TODO
0083
0084       for(G4int i = 0; i < N; ++i)
0085       {
0086         yOut[i] = yIn[i] + h * dydx[i];  // 1st and only Step
0087       }
0088
0089       return;
0090     }
0091
0092     G4int IntegratorOrder() const { return 1; }
0093
0094   private:
0095
0096     T_Equation* fEquation_Rhs;
0097 };
0098
0099 #endif