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1 | /************************************************************************** | |
2 | * Copyright(c) 1998-1999, ALICE Experiment at CERN, All rights reserved. * | |
3 | * * | |
4 | * Author: The ALICE Off-line Project. * | |
5 | * Contributors are mentioned in the code where appropriate. * | |
6 | * * | |
7 | * Permission to use, copy, modify and distribute this software and its * | |
8 | * documentation strictly for non-commercial purposes is hereby granted * | |
9 | * without fee, provided that the above copyright notice appears in all * | |
10 | * copies and that both the copyright notice and this permission notice * | |
11 | * appear in the supporting documentation. The authors make no claims * | |
12 | * about the suitability of this software for any purpose. It is * | |
13 | * provided "as is" without express or implied warranty. * | |
14 | **************************************************************************/ | |
15 | ||
16 | // $Id$ | |
17 | ||
18 | /////////////////////////////////////////////////////////////////////////// | |
19 | // Class AliBoost | |
20 | // Perform various Lorentz transformations. | |
21 | // | |
22 | // Example : | |
23 | // ========= | |
24 | // | |
25 | // Float_t a[3]={0.1,0.2,0.3}; | |
26 | // Float_t ea[3]={0.01,0.02,0.03}; | |
27 | // Ali3Vector beta; | |
28 | // beta.SetVector(a,"car"); | |
29 | // beta.SetErrors(ea,"car"); | |
30 | // | |
31 | // AliBoost b1; | |
32 | // b1.SetBeta(beta); | |
33 | // b1.Data(); | |
34 | // | |
35 | // Float_t b[4]={14,1,2,3}; | |
36 | // Float_t eb[4]={1.4,0.1,0.2,0.3}; | |
37 | // Ali4Vector p; | |
38 | // p.SetVector(b,"car"); | |
39 | // p.SetErrors(eb,"car"); | |
40 | // Ali4Vector pprim=b1.Boost(p); | |
41 | // p.Data(); | |
42 | // pprim.Data(); | |
43 | // | |
44 | // p=b1.Inverse(pprim); | |
45 | // pprim.Data(); | |
46 | // p.Data(); | |
47 | // | |
48 | // Float_t c[4]={5,0,0,4}; | |
49 | // Float_t ec[4]={0.5,0,0,0.4}; | |
50 | // Ali4Vector q; | |
51 | // q.SetVector(c,"car"); | |
52 | // q.SetErrors(ec,"car"); | |
53 | // | |
54 | // AliBoost b2; | |
55 | // b2.Set4Momentum(q); | |
56 | // b2.Data("sph"); | |
57 | // | |
58 | //--- Author: Nick van Eijndhoven 14-may-1996 UU-SAP Utrecht | |
59 | //- Modified: NvE $Date$ UU-SAP Utrecht | |
60 | /////////////////////////////////////////////////////////////////////////// | |
61 | ||
62 | #include "AliBoost.h" | |
63 | ||
64 | ClassImp(AliBoost) // Class implementation to enable ROOT I/O | |
65 | ||
66 | AliBoost::AliBoost() | |
67 | { | |
68 | // Creation of a Lorentz boost object and initialisation of parameters. | |
69 | // Beta is set to (0,0,0) and consequently Gamma=1. | |
70 | // All errors are initialised to 0. | |
71 | Double_t a[3]={0,0,0}; | |
72 | fBeta.SetVector(a,"sph"); | |
73 | fGamma=1; | |
74 | fDgamma=0; | |
75 | fDresult=0; | |
76 | } | |
77 | /////////////////////////////////////////////////////////////////////////// | |
78 | AliBoost::~AliBoost() | |
79 | { | |
80 | // Default destructor. | |
81 | } | |
82 | /////////////////////////////////////////////////////////////////////////// | |
83 | void AliBoost::SetBeta(Ali3Vector b) | |
84 | { | |
85 | // Setting of boost parameters on basis of beta 3-vector. | |
86 | // The errors on the beta 3-vector are taken from the input 3-vector. | |
87 | // The gamma value and its error are calculated accordingly. | |
88 | fBeta=b; | |
89 | Double_t beta2=fBeta.Dot(fBeta); | |
90 | Double_t dbeta2=fBeta.GetResultError(); | |
91 | ||
92 | if (beta2 > 1.) | |
93 | { | |
94 | cout << " *AliBoost::SetBeta* beta > 1." << endl; | |
95 | } | |
96 | fGamma=0; | |
97 | fDgamma=0; | |
98 | Double_t temp=1.-beta2; | |
99 | if (temp > 0.) | |
100 | { | |
101 | fGamma=sqrt(1./temp); | |
102 | fDgamma=fabs(dbeta2/(2.*pow(temp,1.5))); | |
103 | } | |
104 | } | |
105 | /////////////////////////////////////////////////////////////////////////// | |
106 | void AliBoost::Set4Momentum(Ali4Vector& p) | |
107 | { | |
108 | // Setting of boost parameters on basis of momentum 4-vector data. | |
109 | // The errors of the input 4-vector are used to calculate the | |
110 | // errors on the beta 3-vector and the gamma factor. | |
111 | Double_t E=p.GetScalar(); | |
112 | Double_t dE=p.GetResultError(); | |
113 | if (E <= 0.) | |
114 | { | |
115 | cout << " *AliBoost::Set4Momentum* Unphysical situation." << endl; | |
116 | p.Data(); | |
117 | } | |
118 | else | |
119 | { | |
120 | Ali3Vector b=p.Get3Vector(); | |
121 | Double_t vb[3],eb[3]; | |
122 | b.GetVector(vb,"car"); | |
123 | b.GetErrors(eb,"car"); | |
124 | b=b/E; | |
125 | for (Int_t i=0; i<3; i++) | |
126 | { | |
127 | eb[i]=sqrt(pow(eb[i]/E,2)+pow(vb[i]*dE/(E*E),2)); | |
128 | } | |
129 | b.SetErrors(eb,"car"); | |
130 | SetBeta(b); | |
131 | } | |
132 | } | |
133 | /////////////////////////////////////////////////////////////////////////// | |
134 | Ali3Vector AliBoost::GetBetaVector() | |
135 | { | |
136 | // Provide the beta 3-vector. | |
137 | return fBeta; | |
138 | } | |
139 | /////////////////////////////////////////////////////////////////////////// | |
140 | Double_t AliBoost::GetBeta() | |
141 | { | |
142 | // Provide the norm of the beta 3-vector. | |
143 | // The error on the value can be obtained via GetResultError(). | |
144 | Double_t norm=fBeta.GetNorm(); | |
145 | fDresult=fBeta.GetResultError(); | |
146 | return norm; | |
147 | } | |
148 | /////////////////////////////////////////////////////////////////////////// | |
149 | Double_t AliBoost::GetGamma() | |
150 | { | |
151 | // Provide the gamma factor. | |
152 | // The error on the value can be obtained via GetResultError(). | |
153 | fDresult=fDgamma; | |
154 | return fGamma; | |
155 | } | |
156 | /////////////////////////////////////////////////////////////////////////// | |
157 | Double_t AliBoost::GetResultError() | |
158 | { | |
159 | // Provide the error on the result of an operation yielding a scalar. | |
160 | // E.g. GetBeta() or GetGamma() | |
161 | return fDresult; | |
162 | } | |
163 | /////////////////////////////////////////////////////////////////////////// | |
164 | void AliBoost::Data(TString f) | |
165 | { | |
166 | // Printing of the boost parameter info in coordinate frame f. | |
167 | Double_t beta=fBeta.GetNorm(); | |
168 | Double_t dbeta=fBeta.GetResultError(); | |
169 | cout << " *AliBoost::Data* beta : " << beta << " error : " << dbeta | |
170 | << " gamma : " << fGamma << " error : " << fDgamma << endl; | |
171 | cout << " Beta"; | |
172 | fBeta.Data(f); | |
173 | } | |
174 | /////////////////////////////////////////////////////////////////////////// | |
175 | Ali4Vector AliBoost::Boost(Ali4Vector& v) | |
176 | { | |
177 | // Perform the Lorentz boost on the 4-vector v. | |
178 | // Error propagation is performed automatically. | |
179 | // Note : As an approximation Beta and p.Dot(Beta) are considered as | |
180 | // independent quantities. | |
181 | ||
182 | Double_t beta=fBeta.GetNorm(); | |
183 | Double_t dbeta=fBeta.GetResultError(); | |
184 | ||
185 | Double_t beta2=pow(beta,2); | |
186 | ||
187 | if (beta > 1.e-10) | |
188 | { | |
189 | Double_t E=v.GetScalar(); | |
190 | Double_t dE=v.GetResultError(); | |
191 | ||
192 | Ali3Vector p=v.Get3Vector(); | |
193 | ||
194 | Double_t pdotbeta=p.Dot(fBeta); | |
195 | Double_t dpdotbeta=p.GetResultError(); | |
196 | ||
197 | // Determine the new vector components | |
198 | Double_t Eprim=fGamma*(E-pdotbeta); | |
199 | ||
200 | Double_t z=((fGamma-1.)*pdotbeta/beta2)-fGamma*E; | |
201 | Ali3Vector add=fBeta*z; | |
202 | ||
203 | // Determine errors on the new vector components | |
204 | Double_t dEprim=sqrt(pow((E-pdotbeta)*fDgamma,2)+pow(fGamma*dE,2) | |
205 | +pow(fGamma*dpdotbeta,2)); | |
206 | Double_t dz=sqrt( pow(((fGamma-1.)/beta2)*dpdotbeta,2) + pow(fGamma*dE,2) | |
207 | +pow(( | |
208 | ((2./beta)-(4.*pow(beta,3)-6.*pow(beta,5))/(2.*pow((pow(beta,4)-pow(beta,6)),1.5)))*pdotbeta | |
209 | +beta*E/pow(fGamma,3))*dbeta,2) ); | |
210 | ||
211 | Double_t vb[3],eb[3]; | |
212 | fBeta.GetVector(vb,"car"); | |
213 | fBeta.GetErrors(eb,"car"); | |
214 | for (Int_t i=0; i<3; i++) | |
215 | { | |
216 | eb[i]=sqrt(pow(z*eb[i],2)+pow(vb[i]*dz,2)); | |
217 | } | |
218 | add.SetErrors(eb,"car"); | |
219 | ||
220 | // Calculate the new 3-vector | |
221 | Ali3Vector pprim=p+add; | |
222 | ||
223 | // Set the components and errors of the new 4-vector | |
224 | Ali4Vector w; | |
225 | w.SetVector(Eprim,pprim); | |
226 | w.SetScalarError(dEprim); | |
227 | ||
228 | return w; | |
229 | } | |
230 | else | |
231 | { | |
232 | return v; | |
233 | } | |
234 | } | |
235 | /////////////////////////////////////////////////////////////////////////// | |
236 | Ali4Vector AliBoost::Inverse(Ali4Vector& vprim) | |
237 | { | |
238 | // Perform the inverse Lorentz boost on the 4-vector vprim. | |
239 | // Error propagation is performed automatically. | |
240 | // Note : As an approximation Beta and pprim.Dot(Beta) are considered as | |
241 | // independent quantities. | |
242 | ||
243 | Double_t beta=fBeta.GetNorm(); | |
244 | Double_t dbeta=fBeta.GetResultError(); | |
245 | ||
246 | Double_t beta2=pow(beta,2); | |
247 | ||
248 | if (beta > 1.e-10) | |
249 | { | |
250 | Double_t Eprim=vprim.GetScalar(); | |
251 | Double_t dEprim=vprim.GetResultError(); | |
252 | ||
253 | Ali3Vector pprim=vprim.Get3Vector(); | |
254 | ||
255 | Double_t pprimdotbeta=pprim.Dot(fBeta); | |
256 | Double_t dpprimdotbeta=pprim.GetResultError(); | |
257 | ||
258 | // Determine the new vector components | |
259 | Double_t E=fGamma*(Eprim+pprimdotbeta); | |
260 | ||
261 | Double_t z=((fGamma-1.)*pprimdotbeta/beta2)+fGamma*Eprim; | |
262 | Ali3Vector add=fBeta*z; | |
263 | ||
264 | // Determine errors on the prime-vector components | |
265 | Double_t dE=sqrt(pow((Eprim+pprimdotbeta)*fDgamma,2)+pow(fGamma*dEprim,2) | |
266 | +pow(fGamma*dpprimdotbeta,2)); | |
267 | Double_t dz=sqrt( pow(((fGamma-1.)/beta2)*dpprimdotbeta,2) + pow(fGamma*dEprim,2) | |
268 | +pow(( | |
269 | ((2./beta)-(4.*pow(beta,3)-6.*pow(beta,5))/(2.*pow((pow(beta,4)-pow(beta,6)),1.5)))*pprimdotbeta | |
270 | -beta*Eprim/pow(fGamma,3))*dbeta,2) ); | |
271 | ||
272 | Double_t vb[3],eb[3]; | |
273 | fBeta.GetVector(vb,"car"); | |
274 | fBeta.GetErrors(eb,"car"); | |
275 | for (Int_t i=0; i<3; i++) | |
276 | { | |
277 | eb[i]=sqrt(pow(z*eb[i],2)+pow(vb[i]*dz,2)); | |
278 | } | |
279 | add.SetErrors(eb,"car"); | |
280 | ||
281 | // Calculate the new 3-vector | |
282 | Ali3Vector p=pprim+add; | |
283 | ||
284 | // Set the components and errors of the new 4-vector | |
285 | Ali4Vector w; | |
286 | w.SetVector(E,p); | |
287 | w.SetScalarError(dE); | |
288 | ||
289 | return w; | |
290 | } | |
291 | else | |
292 | { | |
293 | return vprim; | |
294 | } | |
295 | } | |
296 | /////////////////////////////////////////////////////////////////////////// |