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25 // 25 //
26 // G4MagErrorStepper implementation <<
27 // 26 //
28 // Author: W.Wander <wwc@mit.edu>, 09.12.1997 << 27 // $Id$
>> 28 //
29 // ------------------------------------------- 29 // --------------------------------------------------------------------
30 30
31 #include "G4MagErrorStepper.hh" 31 #include "G4MagErrorStepper.hh"
32 #include "G4LineSection.hh" 32 #include "G4LineSection.hh"
33 33
34 G4MagErrorStepper::~G4MagErrorStepper() 34 G4MagErrorStepper::~G4MagErrorStepper()
35 { 35 {
36 delete [] yMiddle; << 36 delete[] yMiddle;
37 delete [] dydxMid; << 37 delete[] dydxMid;
38 delete [] yInitial; << 38 delete[] yInitial;
39 delete [] yOneStep; << 39 delete[] yOneStep;
40 } 40 }
41 41
42 void G4MagErrorStepper::Stepper( const G4doubl << 42 void
43 const G4doubl << 43 G4MagErrorStepper::Stepper( const G4double yInput[],
44 G4doubl << 44 const G4double dydx[],
45 G4doubl << 45 G4double hstep,
46 G4doubl << 46 G4double yOutput[],
>> 47 G4double yError [] )
47 { 48 {
48 const G4int nvar = GetNumberOfVariables(); << 49 const G4int nvar = this->GetNumberOfVariables() ;
49 const G4int maxvar = GetNumberOfStateVariab << 50 const G4int maxvar= GetNumberOfStateVariables();
50 51
>> 52 G4int i;
51 // correction for Richardson Extrapolation. 53 // correction for Richardson Extrapolation.
52 // <<
53 G4double correction = 1. / ( (1 << Integra 54 G4double correction = 1. / ( (1 << IntegratorOrder()) -1 );
54 55
55 // Saving yInput because yInput and yOutpu 56 // Saving yInput because yInput and yOutput can be aliases for same array
56 // << 57
57 for(G4int i=0; i<nvar; ++i) << 58 for(i=0;i<nvar;i++) yInitial[i]=yInput[i];
58 { << 59 yInitial[7]= yInput[7]; // Copy the time in case ... even if not really needed
59 yInitial[i]=yInput[i]; <<
60 } <<
61 yInitial[7] = yInput[7]; // Copy the time i <<
62 yMiddle[7] = yInput[7]; // Copy the time f 60 yMiddle[7] = yInput[7]; // Copy the time from initial value
63 yOneStep[7] = yInput[7]; // As it contribut 61 yOneStep[7] = yInput[7]; // As it contributes to final value of yOutput ?
64 // yOutput[7] = yInput[7]; // -> dumb step 62 // yOutput[7] = yInput[7]; // -> dumb stepper does it too for RK4
65 << 63 for(i=nvar;i<maxvar;i++) yOutput[i]=yInput[i];
66 for(G4int i=nvar; i<maxvar; ++i) <<
67 { <<
68 yOutput[i]=yInput[i]; <<
69 } <<
70 // yError[7] = 0.0; 64 // yError[7] = 0.0;
71 65
72 G4double halfStep = hstep * 0.5; 66 G4double halfStep = hstep * 0.5;
73 67
74 // Do two half steps 68 // Do two half steps
75 // << 69
76 DumbStepper (yInitial, dydx, halfStep, 70 DumbStepper (yInitial, dydx, halfStep, yMiddle);
77 RightHandSide(yMiddle, dydxMid); 71 RightHandSide(yMiddle, dydxMid);
78 DumbStepper (yMiddle, dydxMid, halfStep, y 72 DumbStepper (yMiddle, dydxMid, halfStep, yOutput);
79 73
80 // Store midpoint, chord calculation 74 // Store midpoint, chord calculation
81 // << 75
82 fMidPoint = G4ThreeVector( yMiddle[0], yMi 76 fMidPoint = G4ThreeVector( yMiddle[0], yMiddle[1], yMiddle[2]);
83 77
84 // Do a full Step 78 // Do a full Step
85 // <<
86 DumbStepper(yInitial, dydx, hstep, yOneStep 79 DumbStepper(yInitial, dydx, hstep, yOneStep);
87 for(G4int i=0; i<nvar; ++i) << 80 for(i=0;i<nvar;i++) {
88 { <<
89 yError [i] = yOutput[i] - yOneStep[i] ; 81 yError [i] = yOutput[i] - yOneStep[i] ;
90 yOutput[i] += yError[i]*correction ; << 82 yOutput[i] += yError[i]*correction ; // Provides accuracy increased
91 // Provides accuracy increased by 1 or << 83 // by 1 order via the
>> 84 // Richardson Extrapolation
92 } 85 }
93 86
94 fInitialPoint = G4ThreeVector( yInitial[0], 87 fInitialPoint = G4ThreeVector( yInitial[0], yInitial[1], yInitial[2]);
95 fFinalPoint = G4ThreeVector( yOutput[0], 88 fFinalPoint = G4ThreeVector( yOutput[0], yOutput[1], yOutput[2]);
96 89
97 return; << 90 return ;
98 } 91 }
99 92
100 G4double G4MagErrorStepper::DistChord() const << 93
>> 94
>> 95 G4double
>> 96 G4MagErrorStepper::DistChord() const
101 { 97 {
102 // Estimate the maximum distance from the cu 98 // Estimate the maximum distance from the curve to the chord
103 // 99 //
104 // We estimate this using the distance of th << 100 // We estimate this using the distance of the midpoint to
105 // chord (the line between << 101 // chord (the line between
106 // 102 //
107 // Method below is good only for angle devia << 103 // Method below is good only for angle deviations < 2 pi,
108 // This restriction should not a problem for << 104 // This restriction should not a problem for the Runge cutta methods,
109 // which generally cannot integrate accurate << 105 // which generally cannot integrate accurately for large angle deviations.
110 <<
111 G4double distLine, distChord; 106 G4double distLine, distChord;
112 107
113 if (fInitialPoint != fFinalPoint) << 108 if (fInitialPoint != fFinalPoint) {
114 { << 109 distLine= G4LineSection::Distline( fMidPoint, fInitialPoint, fFinalPoint );
115 distLine = G4LineSection::Distline(fMidPo << 110 // This is a class method that gives distance of Mid
116 // This is a class method that gives di << 111 // from the Chord between the Initial and Final points.
117 // from the Chord between the Initial a <<
118 112
119 distChord = distLine; 113 distChord = distLine;
120 } << 114 }else{
121 else <<
122 { <<
123 distChord = (fMidPoint-fInitialPoint).mag 115 distChord = (fMidPoint-fInitialPoint).mag();
124 } 116 }
125 117
126 return distChord; 118 return distChord;
127 } 119 }
>> 120
128 121