include/Geant4/G4TExplicitEuler.hh

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0025 //
0026 // G4TExplicitEuler
0027 //
0028 // Class description:
0029 //
0030 // Templated version of G4ExplicitEuler
0031 //
0032 //
0033 // Created: Josh Xie, June 2014  (supported by Google Summer of Code 2014 )
0034 //
0035 // Supervisors:  Sandro Wenzel, John Apostolakis (CERN)
0036 // Adapted from G4G4TExplicitEuler class
0037 // -------------------------------------------------------------------
0038 //
0039 // Information from G4Explicit Euler:
0040 // ----------------------------------
0041 // Explicit Euler stepper for magnetic field: x_1 = x_0 + h * dx_0.
0042 // The simplistic approach to solving linear differential equations.
0043 // Take the current derivative and add it to the current position.
0044 //
0045 // Created: W.Wander <wwc@mit.edu>, 12.09.1997
0046 // -------------------------------------------------------------------
0047
0048 // --------------------------------------------------------------------
0049 #ifndef G4TExplicitEuler_HH
0050 #define G4TExplicitEuler_HH
0051
0052 #include "G4TMagErrorStepper.hh"
0053 #include "G4ThreeVector.hh"
0054
0055 template <class T_Equation, int N>
0056 class G4TExplicitEuler
0057   : public G4TMagErrorStepper<G4TExplicitEuler<T_Equation, N>, T_Equation, N>
0058 {
0059  public:  // with description
0060   static constexpr double IntegratorCorrection = 1.;
0061
0062   G4TExplicitEuler(T_Equation* EqRhs, G4int numberOfVariables = N)
0063     : G4TMagErrorStepper<G4TExplicitEuler<T_Equation, N>, T_Equation, N>(
0064         EqRhs, numberOfVariables)
0065     , fEquation_Rhs(EqRhs)
0066   {
0067     if( numberOfVariables != N ){
0068        G4ExceptionDescription msg;
0069        msg << "Equation has an incompatible number of variables." ;
0070        msg << "   template N = " << N << " equation-Nvar= "
0071            << numberOfVariables;
0072        G4Exception("G4TExplicitEuler: constructor", "GeomField0003",
0073                    FatalErrorInArgument, msg );
0074     }
0075   }
0076
0077   ~G4TExplicitEuler() { ; }
0078
0079   inline void DumbStepper(const G4double yIn[],
0080                           const G4double dydx[],
0081                           G4double h, G4double yOut[]) // override final
0082   {
0083     // Initialise time to t0, needed when it is not updated by the integration.
0084     // yOut[7] = yIn[7];   //  Better to set it to NaN;  // TODO
0085
0086     for(G4int i = 0; i < N; ++i)
0087     {
0088       yOut[i] = yIn[i] + h * dydx[i];  // 1st and only Step
0089     }
0090
0091     return;
0092   }
0093
0094  public:  // without description
0095   G4int IntegratorOrder() const { return 1; }
0096
0097  private:
0098   T_Equation* fEquation_Rhs;
0099 };
0100
0101 #endif /* G4TExplicitEuler_HH */