1 | // |
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2 | // ******************************************************************** |
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3 | // * License and Disclaimer * |
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4 | // * * |
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6 | // * the Geant4 Collaboration. It is provided under the terms and * |
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8 | // * LICENSE and available at http://cern.ch/geant4/license . These * |
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9 | // * include a list of copyright holders. * |
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10 | // * * |
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11 | // * Neither the authors of this software system, nor their employing * |
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12 | // * institutes,nor the agencies providing financial support for this * |
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13 | // * work make any representation or warranty, express or implied, * |
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14 | // * regarding this software system or assume any liability for its * |
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15 | // * use. Please see the license in the file LICENSE and URL above * |
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16 | // * for the full disclaimer and the limitation of liability. * |
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17 | // * * |
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18 | // * This code implementation is the result of the scientific and * |
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19 | // * technical work of the GEANT4 collaboration. * |
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20 | // * By using, copying, modifying or distributing the software (or * |
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21 | // * any work based on the software) you agree to acknowledge its * |
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22 | // * use in resulting scientific publications, and indicate your * |
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23 | // * acceptance of all terms of the Geant4 Software license. * |
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24 | // ******************************************************************** |
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25 | // |
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26 | // |
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27 | // $Id: G4RKG3_Stepper.cc,v 1.15 2007/08/21 10:17:41 tnikitin Exp $ |
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28 | // GEANT4 tag $Name: geant4-09-04-beta-01 $ |
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29 | // |
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30 | // ------------------------------------------------------------------- |
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31 | |
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32 | #include "G4RKG3_Stepper.hh" |
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33 | #include "G4LineSection.hh" |
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34 | #include "G4Mag_EqRhs.hh" |
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35 | |
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36 | G4RKG3_Stepper::G4RKG3_Stepper(G4Mag_EqRhs *EqRhs) |
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37 | : G4MagIntegratorStepper(EqRhs,6) |
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38 | { |
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39 | |
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40 | fPtrMagEqOfMot=EqRhs; |
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41 | |
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42 | } |
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43 | |
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44 | G4RKG3_Stepper::~G4RKG3_Stepper() |
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45 | { |
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46 | } |
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47 | |
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48 | void G4RKG3_Stepper::Stepper( const G4double yInput[7], |
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49 | const G4double dydx[7], |
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50 | G4double Step, |
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51 | G4double yOut[7], |
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52 | G4double yErr[]) |
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53 | { |
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54 | G4double B[3]; |
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55 | G4int nvar = 6 ; |
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56 | G4int i; |
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57 | G4double by15 = 1. / 15. ; // was 0.066666666 ; |
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58 | |
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59 | G4double yTemp[7], dydxTemp[6], yIn[7] ; |
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60 | // Saving yInput because yInput and yOut can be aliases for same array |
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61 | for(i=0;i<nvar;i++) yIn[i]=yInput[i]; |
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62 | |
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63 | G4double h = Step * 0.5; |
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64 | hStep=Step; |
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65 | // Do two half steps |
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66 | |
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67 | StepNoErr(yIn, dydx,h, yTemp,B) ; |
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68 | |
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69 | //Store Bfld for DistChord Calculation |
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70 | for(i=0;i<3;i++)BfldIn[i]=B[i]; |
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71 | |
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72 | // RightHandSide(yTemp,dydxTemp) ; |
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73 | |
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74 | GetEquationOfMotion()->EvaluateRhsGivenB(yTemp,B,dydxTemp) ; |
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75 | StepNoErr(yTemp,dydxTemp,h,yOut,B); |
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76 | |
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77 | // Store midpoint, chord calculation |
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78 | |
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79 | fyMidPoint = G4ThreeVector( yTemp[0], yTemp[1], yTemp[2]); |
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80 | |
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81 | // Do a full Step |
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82 | |
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83 | h *= 2 ; |
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84 | StepNoErr(yIn,dydx,h,yTemp,B); // ,beTemp2) ; |
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85 | for(i=0;i<nvar;i++) |
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86 | { |
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87 | yErr[i] = yOut[i] - yTemp[i] ; |
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88 | yOut[i] += yErr[i]*by15 ; // Provides 5th order of accuracy |
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89 | } |
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90 | |
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91 | //Store values for DistChord method |
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92 | |
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93 | fyInitial = G4ThreeVector( yIn[0], yIn[1], yIn[2]); |
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94 | fpInitial = G4ThreeVector( yIn[3], yIn[4], yIn[5]); |
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95 | fyFinal = G4ThreeVector( yOut[0], yOut[1], yOut[2]); |
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96 | |
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97 | // NormaliseTangentVector( yOut ); // Deleted |
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98 | } |
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99 | |
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100 | // --------------------------------------------------------------------------- |
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101 | |
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102 | // Integrator for RK from G3 with evaluation of error in solution and delta |
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103 | // geometry based on naive similarity with the case of uniform magnetic field. |
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104 | // B1[3] is input and is the first magnetic field values |
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105 | // B2[3] is output and is the final magnetic field values. |
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106 | |
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107 | void G4RKG3_Stepper::StepWithEst( const G4double*, |
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108 | const G4double*, |
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109 | G4double, |
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110 | G4double*, |
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111 | G4double&, |
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112 | G4double&, |
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113 | const G4double*, |
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114 | G4double* ) |
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115 | |
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116 | { |
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117 | G4Exception("G4RKG3_Stepper::StepWithEst()", "ObsoleteMethod", |
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118 | FatalException, "Method no longer used."); |
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119 | } |
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120 | |
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121 | // ----------------------------------------------------------------- |
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122 | |
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123 | |
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124 | // Integrator RK Stepper from G3 with only two field evaluation per Step. |
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125 | // It is used in propagation initial Step by small substeps after solution |
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126 | // error and delta geometry considerations. B[3] is magnetic field which |
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127 | // is passed from substep to substep. |
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128 | |
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129 | void G4RKG3_Stepper::StepNoErr(const G4double tIn[7], |
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130 | const G4double dydx[7], |
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131 | G4double Step, |
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132 | G4double tOut[7], |
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133 | G4double B[3] ) // const |
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134 | |
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135 | { |
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136 | |
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137 | // Copy and edit the routine above, to delete alpha2, beta2, ... |
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138 | G4double K1[7],K2[7],K3[7],K4[7] ; |
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139 | G4double tTemp[7], yderiv[6] ; |
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140 | |
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141 | // Need Momentum value to give correct values to the coefficients in equation |
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142 | // Integration on unit velocity, but tIn[3,4,5] is momentum |
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143 | G4double mom,inverse_mom; |
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144 | G4int i ; |
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145 | const G4double c1=0.5,c2=0.125,c3=1./6.; |
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146 | |
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147 | // GetEquationOfMotion()->EvaluateRhsReturnB(tIn,dydx,B1) ; |
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148 | // Correction for momentum not a velocity |
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149 | // Need the protection !!! must be not zero |
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150 | mom=std::sqrt(tIn[3]*tIn[3]+tIn[4]*tIn[4]+tIn[5]*tIn[5]); |
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151 | inverse_mom=1./mom; |
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152 | for(i=0;i<3;i++) |
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153 | { |
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154 | K1[i] = Step * dydx[i+3]*inverse_mom; |
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155 | tTemp[i] = tIn[i] + Step*(c1*tIn[i+3]*inverse_mom + c2*K1[i]) ; |
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156 | tTemp[i+3] = tIn[i+3] + c1*K1[i]*mom ; |
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157 | |
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158 | } |
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159 | |
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160 | GetEquationOfMotion()->EvaluateRhsReturnB(tTemp,yderiv,B) ; |
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161 | |
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162 | |
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163 | for(i=0;i<3;i++) |
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164 | { |
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165 | K2[i] = Step * yderiv[i+3]*inverse_mom; |
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166 | tTemp[i+3] = tIn[i+3] + c1*K2[i]*mom ; |
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167 | } |
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168 | |
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169 | // Given B, calculate yderiv ! |
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170 | GetEquationOfMotion()->EvaluateRhsGivenB(tTemp,B,yderiv) ; |
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171 | |
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172 | for(i=0;i<3;i++) |
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173 | { |
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174 | K3[i] = Step * yderiv[i+3]*inverse_mom; |
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175 | tTemp[i] = tIn[i] + Step*(tIn[i+3]*inverse_mom + c1*K3[i]) ; |
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176 | tTemp[i+3] = tIn[i+3] + K3[i]*mom ; |
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177 | } |
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178 | |
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179 | |
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180 | // Calculates y-deriv(atives) & returns B too! |
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181 | GetEquationOfMotion()->EvaluateRhsReturnB(tTemp,yderiv,B) ; |
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182 | |
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183 | |
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184 | for(i=0;i<3;i++) // Output trajectory vector |
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185 | { |
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186 | K4[i] = Step * yderiv[i+3]*inverse_mom; |
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187 | tOut[i] = tIn[i] + Step*(tIn[i+3]*inverse_mom+ (K1[i] + K2[i] + K3[i])*c3) ; |
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188 | tOut[i+3] = tIn[i+3] + mom*(K1[i] + 2*K2[i] + 2*K3[i] +K4[i])*c3 ; |
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189 | } |
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190 | |
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191 | // NormaliseTangentVector( tOut ); |
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192 | |
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193 | |
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194 | } |
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195 | |
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196 | |
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197 | // --------------------------------------------------------------------------- |
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198 | |
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199 | G4double G4RKG3_Stepper::DistChord() const |
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200 | { |
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201 | // Soon: must check whether h/R > 2 pi !! |
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202 | // Method below is good only for < 2 pi |
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203 | G4double distChord,distLine; |
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204 | |
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205 | if (fyInitial != fyFinal) { |
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206 | distLine= G4LineSection::Distline(fyMidPoint,fyInitial,fyFinal ); |
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207 | |
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208 | distChord = distLine; |
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209 | }else{ |
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210 | distChord = (fyMidPoint-fyInitial).mag(); |
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211 | } |
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212 | |
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213 | |
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214 | return distChord; |
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215 | |
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216 | } |
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217 | |
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