G4ImplicitEuler.cc

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00026 //
00027 // $Id: G4ImplicitEuler.cc 69786 2013-05-15 09:38:51Z gcosmo $
00028 //
00029 //
00030 //  Implicit Euler:
00031 //
00032 //        x_1 = x_0 + h/2 * ( dx(t_0,x_0) + dx(t_0+h,x_0+h*dx(t_0,x_0) ) )
00033 //
00034 // Second order solver.
00035 // Take the current derivative and add it to the current position.
00036 // Take the output and its derivative. Add the mean of both derivatives
00037 // to form the final output.
00038 //
00039 // W.Wander <wwc@mit.edu> 12/09/97
00040 //
00041 // --------------------------------------------------------------------
00042 
00043 #include "G4ImplicitEuler.hh"
00044 #include "G4ThreeVector.hh"
00045 
00047 //
00048 // Constructor
00049 
00050 G4ImplicitEuler::G4ImplicitEuler(G4EquationOfMotion *EqRhs, 
00051                                  G4int numberOfVariables): 
00052 G4MagErrorStepper(EqRhs, numberOfVariables)
00053 {
00054   unsigned int noVariables= std::max(numberOfVariables,8); // For Time .. 7+1
00055   dydxTemp = new G4double[noVariables] ;
00056   yTemp    = new G4double[noVariables] ;
00057 }
00058 
00059 
00061 //
00062 // Destructor
00063 
00064 G4ImplicitEuler::~G4ImplicitEuler()
00065 {
00066   delete[] dydxTemp;
00067   delete[] yTemp;
00068 }
00069 
00071 //
00072 //
00073 
00074 void
00075 G4ImplicitEuler::DumbStepper( const G4double  yIn[],
00076                               const G4double  dydx[],
00077                                     G4double  h,
00078                                     G4double  yOut[])
00079 {
00080   G4int i;
00081   const G4int numberOfVariables= GetNumberOfVariables();
00082 
00083   // Initialise time to t0, needed when it is not updated by the integration.
00084   yTemp[7] = yOut[7] = yIn[7];   //  Better to set it to NaN;  // TODO
00085 
00086   for( i = 0; i < numberOfVariables; i++ ) 
00087   {
00088     yTemp[i] = yIn[i] + h*dydx[i] ;          
00089   }
00090   
00091   RightHandSide(yTemp,dydxTemp);
00092   
00093   for( i = 0; i < numberOfVariables; i++ ) 
00094   {
00095     yOut[i] = yIn[i] + 0.5 * h * ( dydx[i] + dydxTemp[i] );
00096   }
00097 
00098   return ;
00099 }  

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