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2 | // ******************************************************************** |
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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: G4ConstRK4.hh,v 1.2 2008/10/29 14:17:42 gcosmo Exp $ |
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28 | // GEANT4 tag $Name: geant4-09-02-cand-01 $ |
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29 | // |
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30 | // |
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31 | // Class G4ConstRK4 |
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32 | // |
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33 | // class description: |
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34 | // |
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35 | // G4ConstRK4 performs the integration of one step with error calculation |
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36 | // in constant magnetic field. The integration method is the same as in |
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37 | // ClassicalRK4. The field value is assumed constant for the step. |
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38 | // This field evaluation is called only once per step. |
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39 | // G4ConstRK4 can be used only for magnetic fields. |
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40 | |
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41 | // History: |
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42 | // - 18.09.2008 - J.Apostolakis, T.Nikitina - Created |
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43 | // ------------------------------------------------------------------- |
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44 | |
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45 | #ifndef G4CONSTRK4_HH |
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46 | #define G4CONSTRK4_HH |
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47 | |
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48 | #include "G4MagErrorStepper.hh" |
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49 | #include "G4EquationOfMotion.hh" |
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50 | #include "G4Mag_EqRhs.hh" |
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51 | |
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52 | class G4ConstRK4 : public G4MagErrorStepper |
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53 | { |
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54 | public: // with description |
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55 | |
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56 | G4ConstRK4(G4Mag_EqRhs *EquationMotion, G4int numberOfVariables = 8); |
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57 | ~G4ConstRK4(); |
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58 | |
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59 | void Stepper( const G4double y[], |
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60 | const G4double dydx[], |
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61 | G4double h, |
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62 | G4double yout[], |
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63 | G4double yerr[] ); |
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64 | void DumbStepper( const G4double yIn[], |
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65 | const G4double dydx[], |
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66 | G4double h, |
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67 | G4double yOut[] ) ; |
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68 | G4double DistChord() const; |
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69 | |
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70 | inline void RightHandSideConst(const G4double y[], |
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71 | G4double dydx[] ) const; |
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72 | |
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73 | inline void GetConstField(const G4double y[],G4double Field[]); |
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74 | |
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75 | public: // without description |
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76 | |
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77 | G4int IntegratorOrder() const { return 4; } |
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78 | |
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79 | private: |
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80 | |
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81 | G4ConstRK4(const G4ConstRK4&); |
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82 | G4ConstRK4& operator=(const G4ConstRK4&); |
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83 | // Private copy constructor and assignment operator. |
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84 | |
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85 | private: |
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86 | |
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87 | G4ThreeVector fInitialPoint, fMidPoint, fFinalPoint; |
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88 | // Data stored in order to find the chord |
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89 | G4double *dydxm, *dydxt, *yt; // scratch space - not state |
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90 | G4double *yInitial, *yMiddle, *dydxMid, *yOneStep; |
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91 | G4Mag_EqRhs *fEq; |
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92 | G4double Field[3]; |
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93 | }; |
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94 | |
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95 | // Inline methods |
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96 | |
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97 | inline void G4ConstRK4:: RightHandSideConst(const G4double y[], |
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98 | G4double dydx[] ) const |
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99 | { |
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100 | |
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101 | G4double momentum_mag_square = y[3]*y[3] + y[4]*y[4] + y[5]*y[5]; |
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102 | G4double inv_momentum_magnitude = 1.0 / std::sqrt( momentum_mag_square ); |
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103 | |
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104 | G4double cof =fEq->FCof()*inv_momentum_magnitude; |
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105 | |
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106 | dydx[0] = y[3]*inv_momentum_magnitude; // (d/ds)x = Vx/V |
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107 | dydx[1] = y[4]*inv_momentum_magnitude; // (d/ds)y = Vy/V |
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108 | dydx[2] = y[5]*inv_momentum_magnitude; // (d/ds)z = Vz/V |
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109 | |
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110 | dydx[3] = cof*(y[4]*Field[2] - y[5]*Field[1]) ; // Ax = a*(Vy*Bz - Vz*By) |
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111 | dydx[4] = cof*(y[5]*Field[0] - y[3]*Field[2]) ; // Ay = a*(Vz*Bx - Vx*Bz) |
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112 | dydx[5] = cof*(y[3]*Field[1] - y[4]*Field[0]) ; // Az = a*(Vx*By - Vy*Bx) |
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113 | } |
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114 | |
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115 | inline void G4ConstRK4::GetConstField(const G4double y[],G4double B[]) |
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116 | { |
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117 | G4double PositionAndTime[4]; |
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118 | |
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119 | PositionAndTime[0] = y[0]; |
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120 | PositionAndTime[1] = y[1]; |
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121 | PositionAndTime[2] = y[2]; |
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122 | // Global Time |
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123 | PositionAndTime[3] = y[7]; |
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124 | fEq -> GetFieldValue(PositionAndTime, B) ; |
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125 | } |
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126 | |
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127 | #endif // G4CONSTRK4_HH |
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