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2 | // ******************************************************************** |
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3 | // * License and Disclaimer * |
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15 | // * use. Please see the license in the file LICENSE and URL above * |
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24 | // ******************************************************************** |
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25 | // |
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26 | // |
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27 | // $Id: G4MagErrorStepper.cc,v 1.13 2006/06/29 18:24:18 gunter Exp $ |
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28 | // GEANT4 tag $Name: HEAD $ |
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29 | // |
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30 | // -------------------------------------------------------------------- |
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31 | |
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32 | #include "G4MagErrorStepper.hh" |
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33 | #include "G4LineSection.hh" |
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34 | |
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35 | G4MagErrorStepper::~G4MagErrorStepper() |
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36 | { |
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37 | delete[] yMiddle; |
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38 | delete[] dydxMid; |
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39 | delete[] yInitial; |
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40 | delete[] yOneStep; |
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41 | } |
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42 | |
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43 | void |
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44 | G4MagErrorStepper::Stepper( const G4double yInput[], |
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45 | const G4double dydx[], |
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46 | G4double hstep, |
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47 | G4double yOutput[], |
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48 | G4double yError [] ) |
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49 | { |
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50 | const G4int nvar = this->GetNumberOfVariables() ; |
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51 | const G4int maxvar= GetNumberOfStateVariables(); |
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52 | |
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53 | G4int i; |
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54 | // correction for Richardson Extrapolation. |
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55 | G4double correction = 1. / ( (1 << IntegratorOrder()) -1 ); |
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56 | |
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57 | // Saving yInput because yInput and yOutput can be aliases for same array |
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58 | |
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59 | for(i=0;i<nvar;i++) yInitial[i]=yInput[i]; |
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60 | yInitial[7]= yInput[7]; // Copy the time in case ... even if not really needed |
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61 | yMiddle[7] = yInput[7]; // Copy the time from initial value |
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62 | yOneStep[7] = yInput[7]; // As it contributes to final value of yOutput ? |
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63 | // yOutput[7] = yInput[7]; // -> dumb stepper does it too for RK4 |
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64 | for(i=nvar;i<maxvar;i++) yOutput[i]=yInput[i]; |
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65 | // yError[7] = 0.0; |
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66 | |
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67 | G4double halfStep = hstep * 0.5; |
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68 | |
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69 | // Do two half steps |
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70 | |
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71 | DumbStepper (yInitial, dydx, halfStep, yMiddle); |
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72 | RightHandSide(yMiddle, dydxMid); |
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73 | DumbStepper (yMiddle, dydxMid, halfStep, yOutput); |
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74 | |
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75 | // Store midpoint, chord calculation |
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76 | |
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77 | fMidPoint = G4ThreeVector( yMiddle[0], yMiddle[1], yMiddle[2]); |
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78 | |
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79 | // Do a full Step |
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80 | DumbStepper(yInitial, dydx, hstep, yOneStep); |
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81 | for(i=0;i<nvar;i++) { |
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82 | yError [i] = yOutput[i] - yOneStep[i] ; |
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83 | yOutput[i] += yError[i]*correction ; // Provides accuracy increased |
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84 | // by 1 order via the |
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85 | // Richardson Extrapolation |
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86 | } |
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87 | |
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88 | fInitialPoint = G4ThreeVector( yInitial[0], yInitial[1], yInitial[2]); |
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89 | fFinalPoint = G4ThreeVector( yOutput[0], yOutput[1], yOutput[2]); |
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90 | |
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91 | return ; |
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92 | } |
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93 | |
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94 | |
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95 | |
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96 | G4double |
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97 | G4MagErrorStepper::DistChord() const |
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98 | { |
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99 | // Estimate the maximum distance from the curve to the chord |
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100 | // |
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101 | // We estimate this using the distance of the midpoint to |
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102 | // chord (the line between |
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103 | // |
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104 | // Method below is good only for angle deviations < 2 pi, |
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105 | // This restriction should not a problem for the Runge cutta methods, |
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106 | // which generally cannot integrate accurately for large angle deviations. |
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107 | G4double distLine, distChord; |
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108 | |
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109 | if (fInitialPoint != fFinalPoint) { |
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110 | distLine= G4LineSection::Distline( fMidPoint, fInitialPoint, fFinalPoint ); |
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111 | // This is a class method that gives distance of Mid |
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112 | // from the Chord between the Initial and Final points. |
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113 | |
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114 | distChord = distLine; |
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115 | }else{ |
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116 | distChord = (fMidPoint-fInitialPoint).mag(); |
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117 | } |
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118 | |
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119 | return distChord; |
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120 | } |
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121 | |
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