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25 //
26 // G4ClassicalRK4 implementation
27 //
28 // Created: J.Apostolakis, V.Grichine - 30.01.1997
29 // -------------------------------------------------------------------
30
31 #include "G4ClassicalRK4.hh"
32 #include "G4ThreeVector.hh"
33
34 //////////////////////////////////////////////////////////////////
35 //
36 // Constructor sets the number of variables (default = 6)
37 //
38 G4ClassicalRK4::
39 G4ClassicalRK4(G4EquationOfMotion* EqRhs, G4int numberOfVariables)
40 : G4MagErrorStepper(EqRhs, numberOfVariables)
41 {
42 unsigned int noVariables= std::max(numberOfVariables,8); // For Time .. 7+1
43
44 dydxm = new G4double[noVariables];
45 dydxt = new G4double[noVariables];
46 yt = new G4double[noVariables];
47 }
48
49 ////////////////////////////////////////////////////////////////
50 //
51 // Destructor
52 //
53 G4ClassicalRK4::~G4ClassicalRK4()
54 {
55 delete [] dydxm;
56 delete [] dydxt;
57 delete [] yt;
58 }
59
60 //////////////////////////////////////////////////////////////////////
61 //
62 // Given values for the variables y[0,..,n-1] and their derivatives
63 // dydx[0,...,n-1] known at x, use the classical 4th Runge-Kutta
64 // method to advance the solution over an interval h and return the
65 // incremented variables as yout[0,...,n-1], which not be a distinct
66 // array from y. The user supplies the routine RightHandSide(x,y,dydx),
67 // which returns derivatives dydx at x. The source is routine rk4 from
68 // NRC p. 712-713 .
69 //
70 void
71 G4ClassicalRK4::DumbStepper( const G4double yIn[],
72 const G4double dydx[],
73 G4double h,
74 G4double yOut[])
75 {
76 const G4int nvar = GetNumberOfVariables(); // fNumberOfVariables();
77 G4int i;
78 G4double hh = h*0.5, h6 = h/6.0;
79
80 // Initialise time to t0, needed when it is not updated by the integration.
81 // [ Note: Only for time dependent fields (usually electric)
82 // is it neccessary to integrate the time.]
83 yt[7] = yIn[7];
84 yOut[7] = yIn[7];
85
86 for(i=0; i<nvar; ++i)
87 {
88 yt[i] = yIn[i] + hh*dydx[i] ; // 1st Step K1=h*dydx
89 }
90 RightHandSide(yt,dydxt) ; // 2nd Step K2=h*dydxt
91
92 for(i=0; i<nvar; ++i)
93 {
94 yt[i] = yIn[i] + hh*dydxt[i] ;
95 }
96 RightHandSide(yt,dydxm) ; // 3rd Step K3=h*dydxm
97
98 for(i=0; i<nvar; ++i)
99 {
100 yt[i] = yIn[i] + h*dydxm[i] ;
101 dydxm[i] += dydxt[i] ; // now dydxm=(K2+K3)/h
102 }
103 RightHandSide(yt,dydxt) ; // 4th Step K4=h*dydxt
104
105 for(i=0; i<nvar; ++i) // Final RK4 output
106 {
107 yOut[i] = yIn[i]+h6*(dydx[i]+dydxt[i]+2.0*dydxm[i]); //+K1/6+K4/6+(K2+K3)/3
108 }
109 if ( nvar == 12 ) { NormalisePolarizationVector ( yOut ); }
110
111 } // end of DumbStepper ....................................................
112
113 ////////////////////////////////////////////////////////////////////
114 //
115 // StepWithEst
116
117 void
118 G4ClassicalRK4::StepWithEst( const G4double*,
119 const G4double*,
120 G4double,
121 G4double*,
122 G4double&,
123 G4double&,
124 const G4double*,
125 G4double* )
126 {
127 G4Exception("G4ClassicalRK4::StepWithEst()", "GeomField0001",
128 FatalException, "Method no longer used.");
129
130 } // end of StepWithEst ......................................................
131