Geant4 Cross Reference

Cross-Referencing   Geant4
Geant4/externals/clhep/src/LorentzVectorB.cc

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  1 // -*- C++ -*-
  2 // ---------------------------------------------------------------------------
  3 //
  4 // This file is a part of the CLHEP - a Class Library for High Energy Physics.
  5 //
  6 // This is the implementation of the HepLorentzVector class:
  7 // Those methods originating in ZOOM dealing with simple boosts and rotations.
  8 // Use of one of these methods will not force loading of the HepRotation or
  9 // HepLorentzRotation class.
 10 //
 11 
 12 #include "CLHEP/Vector/LorentzVector.h"
 13 
 14 #include <cmath>
 15 #include <iostream>
 16 
 17 namespace CLHEP  {
 18 
 19 //-*********
 20 // rotationOf()
 21 //-*********
 22 
 23 // Each of these is a shell over a rotate method.
 24 
 25 HepLorentzVector rotationXOf
 26   (const HepLorentzVector & vec, double phi){
 27   HepLorentzVector vv (vec);
 28   return vv.rotateX (phi);
 29 }
 30 
 31 HepLorentzVector rotationYOf
 32   (const HepLorentzVector & vec, double phi){
 33   HepLorentzVector vv (vec);
 34   return vv.rotateY (phi);
 35 }
 36 
 37 HepLorentzVector rotationZOf
 38   (const HepLorentzVector & vec, double phi){
 39   HepLorentzVector vv (vec);
 40   return vv.rotateZ (phi);
 41 }
 42 
 43 //-********
 44 // boost
 45 //-********
 46 
 47 HepLorentzVector & HepLorentzVector::boost 
 48       ( const Hep3Vector & aaxis,  double bbeta ) {
 49   if (bbeta==0) {
 50     return *this; // do nothing for a 0 boost
 51   }
 52   double r2 = aaxis.mag2();
 53   if ( r2 == 0 ) {
 54     std::cerr << "HepLorentzVector::boost() - "
 55       << "A zero vector used as axis defining a boost -- no boost done"
 56       << std::endl;
 57     return *this;
 58   } 
 59   double b2 = bbeta*bbeta;
 60   if (b2 >= 1) {
 61     std::cerr << "HepLorentzVector::boost() - "
 62       << "LorentzVector boosted with beta >= 1 (speed of light) -- \n"
 63       << "no boost done" << std::endl;
 64   } else {
 65     Hep3Vector u = aaxis.unit();
 66     double ggamma = std::sqrt(1./(1.-b2));
 67     double betaDotV = u.dot(pp)*bbeta;
 68     double tt = ee;
 69 
 70     ee = ggamma * (tt + betaDotV);
 71     pp += ( ((ggamma-1)/b2)*betaDotV*bbeta + ggamma*bbeta*tt ) * u;
 72     // Note:  I have verified the behavior of this even when beta is very
 73     //        small -- (gamma-1)/b2 becomes inaccurate by O(1), but it is then
 74     //        multiplied by O(beta**2) and added to an O(beta) term, so the
 75     //        inaccuracy does not affect the final result.
 76   }
 77   return *this;
 78 } /* boost (axis, beta) */
 79 
 80 }  // namespace CLHEP
 81