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25 // 25 //
26 // G4ClassicalRK4 implementation <<
27 // 26 //
28 // Created: J.Apostolakis, V.Grichine - 30.01. << 27 // $Id: G4ClassicalRK4.cc,v 1.14 2009/03/25 15:29:02 gcosmo Exp $
>> 28 // GEANT4 tag $Name: geant4-09-03-patch-01 $
>> 29 //
29 // ------------------------------------------- 30 // -------------------------------------------------------------------
30 31
31 #include "G4ClassicalRK4.hh" 32 #include "G4ClassicalRK4.hh"
32 #include "G4ThreeVector.hh" 33 #include "G4ThreeVector.hh"
33 34
34 ////////////////////////////////////////////// 35 //////////////////////////////////////////////////////////////////
35 // 36 //
36 // Constructor sets the number of variables (d 37 // Constructor sets the number of variables (default = 6)
37 // << 38
38 G4ClassicalRK4:: 39 G4ClassicalRK4::
39 G4ClassicalRK4(G4EquationOfMotion* EqRhs, G4in 40 G4ClassicalRK4(G4EquationOfMotion* EqRhs, G4int numberOfVariables)
40 : G4MagErrorStepper(EqRhs, numberOfVariables 41 : G4MagErrorStepper(EqRhs, numberOfVariables)
41 { 42 {
42 unsigned int noVariables= std::max(numberOf 43 unsigned int noVariables= std::max(numberOfVariables,8); // For Time .. 7+1
43 44
44 dydxm = new G4double[noVariables]; 45 dydxm = new G4double[noVariables];
45 dydxt = new G4double[noVariables]; 46 dydxt = new G4double[noVariables];
46 yt = new G4double[noVariables]; 47 yt = new G4double[noVariables];
47 } 48 }
48 49
49 ////////////////////////////////////////////// 50 ////////////////////////////////////////////////////////////////
50 // 51 //
51 // Destructor 52 // Destructor
52 // << 53
53 G4ClassicalRK4::~G4ClassicalRK4() 54 G4ClassicalRK4::~G4ClassicalRK4()
54 { 55 {
55 delete [] dydxm; << 56 delete[] dydxm;
56 delete [] dydxt; << 57 delete[] dydxt;
57 delete [] yt; << 58 delete[] yt;
58 } 59 }
59 60
60 ////////////////////////////////////////////// 61 //////////////////////////////////////////////////////////////////////
61 // 62 //
62 // Given values for the variables y[0,..,n-1] 63 // Given values for the variables y[0,..,n-1] and their derivatives
63 // dydx[0,...,n-1] known at x, use the classic 64 // dydx[0,...,n-1] known at x, use the classical 4th Runge-Kutta
64 // method to advance the solution over an inte 65 // method to advance the solution over an interval h and return the
65 // incremented variables as yout[0,...,n-1], w 66 // incremented variables as yout[0,...,n-1], which not be a distinct
66 // array from y. The user supplies the routine 67 // array from y. The user supplies the routine RightHandSide(x,y,dydx),
67 // which returns derivatives dydx at x. The so 68 // which returns derivatives dydx at x. The source is routine rk4 from
68 // NRC p. 712-713 . 69 // NRC p. 712-713 .
69 // << 70
70 void 71 void
71 G4ClassicalRK4::DumbStepper( const G4double yI << 72 G4ClassicalRK4::DumbStepper( const G4double yIn[],
72 const G4double dy << 73 const G4double dydx[],
73 G4double h, << 74 G4double h,
74 G4double yO << 75 G4double yOut[])
75 { 76 {
76 const G4int nvar = GetNumberOfVariables(); << 77 const G4int nvar = this->GetNumberOfVariables(); // fNumberOfVariables();
77 G4int i; 78 G4int i;
78 G4double hh = h*0.5, h6 = h/6.0; << 79 G4double hh = h*0.5 , h6 = h/6.0 ;
79 80
80 // Initialise time to t0, needed when it is 81 // Initialise time to t0, needed when it is not updated by the integration.
81 // [ Note: Only for time dependent fi 82 // [ Note: Only for time dependent fields (usually electric)
82 // is it neccessary to inte 83 // is it neccessary to integrate the time.]
83 yt[7] = yIn[7]; 84 yt[7] = yIn[7];
84 yOut[7] = yIn[7]; 85 yOut[7] = yIn[7];
85 86
86 for(i=0; i<nvar; ++i) << 87 for(i=0;i<nvar;i++)
87 { 88 {
88 yt[i] = yIn[i] + hh*dydx[i] ; 89 yt[i] = yIn[i] + hh*dydx[i] ; // 1st Step K1=h*dydx
89 } 90 }
90 RightHandSide(yt,dydxt) ; 91 RightHandSide(yt,dydxt) ; // 2nd Step K2=h*dydxt
91 92
92 for(i=0; i<nvar; ++i) << 93 for(i=0;i<nvar;i++)
93 { 94 {
94 yt[i] = yIn[i] + hh*dydxt[i] ; 95 yt[i] = yIn[i] + hh*dydxt[i] ;
95 } 96 }
96 RightHandSide(yt,dydxm) ; 97 RightHandSide(yt,dydxm) ; // 3rd Step K3=h*dydxm
97 98
98 for(i=0; i<nvar; ++i) << 99 for(i=0;i<nvar;i++)
99 { 100 {
100 yt[i] = yIn[i] + h*dydxm[i] ; << 101 yt[i] = yIn[i] + h*dydxm[i] ;
101 dydxm[i] += dydxt[i] ; 102 dydxm[i] += dydxt[i] ; // now dydxm=(K2+K3)/h
102 } 103 }
103 RightHandSide(yt,dydxt) ; 104 RightHandSide(yt,dydxt) ; // 4th Step K4=h*dydxt
104 105
105 for(i=0; i<nvar; ++i) // Final RK4 output << 106 for(i=0;i<nvar;i++) // Final RK4 output
106 { 107 {
107 yOut[i] = yIn[i]+h6*(dydx[i]+dydxt[i]+2.0* 108 yOut[i] = yIn[i]+h6*(dydx[i]+dydxt[i]+2.0*dydxm[i]); //+K1/6+K4/6+(K2+K3)/3
108 } 109 }
109 if ( nvar == 12 ) { NormalisePolarizationVe 110 if ( nvar == 12 ) { NormalisePolarizationVector ( yOut ); }
110 111
111 } // end of DumbStepper ..................... 112 } // end of DumbStepper ....................................................
112 113
113 ////////////////////////////////////////////// 114 ////////////////////////////////////////////////////////////////////
114 // 115 //
115 // StepWithEst 116 // StepWithEst
116 117
117 void 118 void
118 G4ClassicalRK4::StepWithEst( const G4double*, 119 G4ClassicalRK4::StepWithEst( const G4double*,
119 const G4double*, 120 const G4double*,
120 G4double, 121 G4double,
121 G4double*, 122 G4double*,
122 G4double&, 123 G4double&,
123 G4double&, 124 G4double&,
124 const G4double*, 125 const G4double*,
125 G4double* 126 G4double* )
126 { 127 {
127 G4Exception("G4ClassicalRK4::StepWithEst()", << 128 G4Exception("G4ClassicalRK4::StepWithEst()", "ObsoleteMethod",
128 FatalException, "Method no longe 129 FatalException, "Method no longer used.");
129 130
130 } // end of StepWithEst ..................... 131 } // end of StepWithEst ......................................................
>> 132
131 133