G4StokesVector.cc

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// $Id: G4StokesVector.cc 69847 2013-05-16 09:36:18Z gcosmo $
//
// GEANT4 Class file
//
//
// File name:     G4StokesVector
//
// Author:        Andreas Schaelicke
//
// Creation date: 01.05.2005
//
// Modifications:
//
// Class Description:
//
// Provides Stokesvector representation employed in polarized 
// processes.
//
#include "G4StokesVector.hh"
#include "G4PolarizationHelper.hh"
#include "G4PhysicalConstants.hh"
#include "Randomize.hh"

const G4StokesVector G4StokesVector::ZERO=G4ThreeVector(0.,0.,0.);
const G4StokesVector G4StokesVector::P1=G4ThreeVector(1.,0.,0.);
const G4StokesVector G4StokesVector::P2=G4ThreeVector(0.,1.,0.);
const G4StokesVector G4StokesVector::P3=G4ThreeVector(0.,0.,1.);
const G4StokesVector G4StokesVector::M1=G4ThreeVector(-1.,0.,0.);
const G4StokesVector G4StokesVector::M2=G4ThreeVector(0.,-1.,0.);
const G4StokesVector G4StokesVector::M3=G4ThreeVector(0.,0.,-1.);

G4StokesVector::G4StokesVector()
  : G4ThreeVector(),isPhoton(false)
{
}

G4StokesVector::G4StokesVector(const G4ThreeVector & v)
  : G4ThreeVector(v),isPhoton(false)
{
}

G4StokesVector::~G4StokesVector()
{
}

void G4StokesVector::RotateAz(G4ThreeVector nInteractionFrame, 
                              G4ThreeVector particleDirection) 
{
  G4ThreeVector  yParticleFrame = 
    G4PolarizationHelper::GetParticleFrameY(particleDirection);


  G4double cosphi=yParticleFrame*nInteractionFrame;
  if (cosphi>(1.+1.e-8) || cosphi<(-1.-1.e-8)) {
    G4cout<<" warning G4StokesVector::RotateAz  cosphi>1 or cosphi<-1\n"
          <<" cosphi="<<cosphi<<"\n"
          <<" zAxis="<<particleDirection<<" ("<<particleDirection.mag()<<")\n"
          <<" yAxis="<<yParticleFrame<<" ("<<yParticleFrame.mag()<<")\n"
          <<" nAxis="<<nInteractionFrame<<" ("
          <<nInteractionFrame.mag()<<")"<<G4endl;
  }
  if (cosphi>1.) cosphi=1.;
  else if (cosphi<-1.) cosphi=-1.;

//     G4cout<<" cosphi="<<cosphi<<"\n"
//        <<" zAxis="<<particleDirection<<" ("<<particleDirection.mag()<<")\n"
//        <<" yAxis="<<yParticleFrame<<" ("<<yParticleFrame.mag()<<","<<(yParticleFrame*particleDirection)<<")\n"
//        <<" nAxis="<<nInteractionFrame<<" ("
//        <<nInteractionFrame.mag()<<")"<<G4endl;

  //  G4double hel=sgn(cross(yParticleFrame*nInteractionFrame)*zInteractionFrame);
  // Why not particleDirection instead of zInteractionFrame ???!!!
  // -> is the same, since SYSIN is called with p1, and p2 as first parameter!
  G4double hel=(yParticleFrame.cross(nInteractionFrame)*particleDirection)>0?1.:-1.;

  G4double sinphi=hel*std::sqrt(1.-cosphi*cosphi);
  //  G4cout<<" sin2 + cos2 -1 = "<<(sinphi*sinphi+cosphi*cosphi-1)<<"\n";

  RotateAz(cosphi,sinphi);
}


void G4StokesVector::InvRotateAz(G4ThreeVector nInteractionFrame, 
                                 G4ThreeVector particleDirection)
{
  // note if incomming particle is on z-axis, 
  // we might encounter some nummerical problems, since
  // nInteratonFrame and yParticleFrame are actually (almost) the same momentum
  // and the normalization is only good to 10^-12 !

  G4ThreeVector  yParticleFrame = 
    G4PolarizationHelper::GetParticleFrameY(particleDirection);
  G4double cosphi=yParticleFrame*nInteractionFrame;

  if (cosphi>1.+1.e-8 || cosphi<-1.-1.e-8) {
        G4cout<<" warning G4StokesVector::RotateAz  cosphi>1 or cosphi<-1\n";
  }
  if (cosphi>1) cosphi=1.;
  else if (cosphi<-1)cosphi=-1.;

  // check sign once more!
  G4double hel=(yParticleFrame.cross(nInteractionFrame)*particleDirection)>0?1.:-1.;
  G4double sinphi=hel*std::sqrt(std::fabs(1.-cosphi*cosphi));
  RotateAz(cosphi,-sinphi);
}

void G4StokesVector::RotateAz(G4double cosphi, G4double sinphi) 
{
  if (!isPhoton) {
    G4double xsi1=  cosphi*p1() + sinphi*p2();
    G4double xsi2= -sinphi*p1() + cosphi*p2();
    setX(xsi1);
    setY(xsi2);
    return;
  }

  G4double sin2phi=2.*cosphi*sinphi;
  G4double cos2phi=cosphi*cosphi-sinphi*sinphi;

  G4double xsi1=  cos2phi*p1() + sin2phi*p2();
  G4double xsi2= -sin2phi*p1() + cos2phi*p2();
  setX(xsi1);
  setY(xsi2);
}

G4double G4StokesVector::GetBeta() 
{
  G4double bet=getPhi();
  if (isPhoton) { bet *= 0.5; }
  return bet;
}

void G4StokesVector::DiceUniform() 
{
  G4double costheta=2.*G4UniformRand()-1.;
  G4double sintheta=std::sqrt(1.-costheta*costheta);
  G4double aphi     =2.*pi*G4UniformRand();
  setX(std::sin(aphi)*sintheta);
  setY(std::cos(aphi)*sintheta);
  setZ(costheta);
}

void G4StokesVector::DiceP1() 
{
  if (G4UniformRand()>0.5) setX(1.);
  else setX(-1.);
  setY(0.);
  setZ(0.);
}

void G4StokesVector::DiceP2() 
{
  setX(0.);
  if (G4UniformRand()>0.5) setY(1.);
  else setY(-1.);
  setZ(0.);
}

void G4StokesVector::DiceP3() 
{
  setX(0.);
  setY(0.);
  if (G4UniformRand()>0.5) setZ(1.);
  else setZ(-1.);
}

void G4StokesVector::FlipP3() 
{
  setZ(-z());
}

G4ThreeVector G4StokesVector::PolError(const G4StokesVector & sum2, long n)
{
  // delta x = sqrt[ ( <x^2> - <x>^2 )/(n-1) ]
  G4StokesVector mean=(1./n)*(*this);
  return G4StokesVector((1./(n-1.)*((1./n)*sum2 - mean.PolSqr()))).PolSqrt();
}

G4ThreeVector G4StokesVector::PolDiv(const G4StokesVector & b)
  {return G4ThreeVector(b.x()!=0. ? x()/b.x() : 11111.,
                        b.y()!=0. ? y()/b.y() : 11111., 
                        b.z()!=0. ? z()/b.z() : 11111.);}

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