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25 //
26 // Geant4 Class file
27 //
28 // File name: G4StokesVector
29 //
30 // Author: Andreas Schaelicke
31 //
32 // Class Description:
33 // Provides Stokes vector representation employed in polarized processes.
34
35 #include "G4StokesVector.hh"
36
37 #include "G4PolarizationHelper.hh"
38 #include "Randomize.hh"
39
40 const G4StokesVector G4StokesVector::ZERO =
41 G4StokesVector(G4ThreeVector(0., 0., 0.));
42 const G4StokesVector G4StokesVector::P1 =
43 G4StokesVector(G4ThreeVector(1., 0., 0.));
44 const G4StokesVector G4StokesVector::P2 =
45 G4StokesVector(G4ThreeVector(0., 1., 0.));
46 const G4StokesVector G4StokesVector::P3 =
47 G4StokesVector(G4ThreeVector(0., 0., 1.));
48 const G4StokesVector G4StokesVector::M1 =
49 G4StokesVector(G4ThreeVector(-1., 0., 0.));
50 const G4StokesVector G4StokesVector::M2 =
51 G4StokesVector(G4ThreeVector(0., -1., 0.));
52 const G4StokesVector G4StokesVector::M3 =
53 G4StokesVector(G4ThreeVector(0., 0., -1.));
54
55 G4StokesVector::G4StokesVector()
56 : G4ThreeVector()
57 , fIsPhoton(false)
58 {}
59
60 G4StokesVector::G4StokesVector(const G4ThreeVector& v)
61 : G4ThreeVector(v)
62 , fIsPhoton(false)
63 {}
64
65 G4bool G4StokesVector::IsZero() const { return *this == ZERO; }
66
67 void G4StokesVector::RotateAz(G4ThreeVector nInteractionFrame,
68 G4ThreeVector particleDirection)
69 {
70 G4ThreeVector yParticleFrame =
71 G4PolarizationHelper::GetParticleFrameY(particleDirection);
72
73 G4double cosphi = yParticleFrame * nInteractionFrame;
74 if(cosphi > (1. + 1.e-8) || cosphi < (-1. - 1.e-8))
75 {
76 G4ExceptionDescription ed;
77 ed << " warning G4StokesVector::RotateAz cosphi>1 or cosphi<-1\n"
78 << " cosphi=" << cosphi << "\n"
79 << " zAxis=" << particleDirection << " (" << particleDirection.mag()
80 << ")\n"
81 << " yAxis=" << yParticleFrame << " (" << yParticleFrame.mag() << ")\n"
82 << " nAxis=" << nInteractionFrame << " (" << nInteractionFrame.mag()
83 << ")\n";
84 G4Exception("G4StokesVector::RotateAz", "pol030", JustWarning, ed);
85 }
86 if(cosphi > 1.)
87 cosphi = 1.;
88 else if(cosphi < -1.)
89 cosphi = -1.;
90
91 G4double hel =
92 (yParticleFrame.cross(nInteractionFrame) * particleDirection) > 0. ? 1.
93 : -1.;
94
95 G4double sinphi = hel * std::sqrt(1. - cosphi * cosphi);
96
97 RotateAz(cosphi, sinphi);
98 }
99
100 void G4StokesVector::InvRotateAz(G4ThreeVector nInteractionFrame,
101 G4ThreeVector particleDirection)
102 {
103 // note if incoming particle is on z-axis,
104 // we might encounter some nummerical problems, since
105 // nInteratonFrame and yParticleFrame are actually (almost) the same momentum
106 // and the normalization is only good to 10^-12 !
107
108 G4ThreeVector yParticleFrame =
109 G4PolarizationHelper::GetParticleFrameY(particleDirection);
110 G4double cosphi = yParticleFrame * nInteractionFrame;
111
112 if(cosphi > 1. + 1.e-8 || cosphi < -1. - 1.e-8)
113 {
114 G4ExceptionDescription ed;
115 ed << " warning G4StokesVector::RotateAz cosphi>1 or cosphi<-1\n";
116 G4Exception("G4StokesVector::InvRotateAz", "pol030", JustWarning, ed);
117 }
118 if(cosphi > 1.)
119 cosphi = 1.;
120 else if(cosphi < -1.)
121 cosphi = -1.;
122
123 // check sign once more!
124 G4double hel =
125 (yParticleFrame.cross(nInteractionFrame) * particleDirection) > 0. ? 1.
126 : -1.;
127 G4double sinphi = hel * std::sqrt(std::fabs(1. - cosphi * cosphi));
128 RotateAz(cosphi, -sinphi);
129 }
130
131 void G4StokesVector::RotateAz(G4double cosphi, G4double sinphi)
132 {
133 if(!fIsPhoton)
134 {
135 G4double xsi1 = cosphi * p1() + sinphi * p2();
136 G4double xsi2 = -sinphi * p1() + cosphi * p2();
137 setX(xsi1);
138 setY(xsi2);
139 return;
140 }
141
142 G4double sin2phi = 2. * cosphi * sinphi;
143 G4double cos2phi = cosphi * cosphi - sinphi * sinphi;
144
145 G4double xsi1 = cos2phi * p1() + sin2phi * p2();
146 G4double xsi2 = -sin2phi * p1() + cos2phi * p2();
147 setX(xsi1);
148 setY(xsi2);
149 }
150
151 G4double G4StokesVector::GetBeta()
152 {
153 G4double bet = getPhi();
154 if(fIsPhoton)
155 {
156 bet *= 0.5;
157 }
158 return bet;
159 }
160
161 void G4StokesVector::DiceUniform()
162 {
163 G4double costheta = 2. * G4UniformRand() - 1.;
164 G4double sintheta = std::sqrt(1. - costheta * costheta);
165 G4double aphi = 2. * CLHEP::pi * G4UniformRand();
166 setX(std::sin(aphi) * sintheta);
167 setY(std::cos(aphi) * sintheta);
168 setZ(costheta);
169 }
170
171 void G4StokesVector::DiceP1()
172 {
173 if(G4UniformRand() > 0.5)
174 setX(1.);
175 else
176 setX(-1.);
177 setY(0.);
178 setZ(0.);
179 }
180
181 void G4StokesVector::DiceP2()
182 {
183 setX(0.);
184 if(G4UniformRand() > 0.5)
185 setY(1.);
186 else
187 setY(-1.);
188 setZ(0.);
189 }
190
191 void G4StokesVector::DiceP3()
192 {
193 setX(0.);
194 setY(0.);
195 if(G4UniformRand() > 0.5)
196 setZ(1.);
197 else
198 setZ(-1.);
199 }
200
201 void G4StokesVector::FlipP3() { setZ(-z()); }
202
203 G4ThreeVector G4StokesVector::PolError(const G4StokesVector& sum2, long n)
204 {
205 // delta x = sqrt[ ( <x^2> - <x>^2 )/(n-1) ]
206 G4ThreeVector mean = (1. / n) * G4ThreeVector(*this);
207 G4ThreeVector polsqr = G4StokesVector(mean).PolSqr();
208 G4ThreeVector result =
209 G4StokesVector((1. / (n - 1.) * ((1. / n) * sum2 - polsqr))).PolSqrt();
210 return result;
211 }
212
213 G4ThreeVector G4StokesVector::PolDiv(const G4StokesVector& b)
214 {
215 return G4ThreeVector(b.x() != 0. ? x() / b.x() : 11111.,
216 b.y() != 0. ? y() / b.y() : 11111.,
217 b.z() != 0. ? z() / b.z() : 11111.);
218 }
219