G4QuadrupoleMagField.cc

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//
// G4QuadrupoleMagField implementation
//
// 03.02.1997, V.Grichine - Created
// 11.05.2012, B.Riese  - Allow displaced origin and rotation
// -------------------------------------------------------------------
 
#include "G4QuadrupoleMagField.hh"
#include "G4RotationMatrix.hh"
 
namespace
{
   G4RotationMatrix IdentityMatrix; 
}
 
G4QuadrupoleMagField::G4QuadrupoleMagField(G4double pGradient)
{
   fGradient = pGradient;
   fpMatrix  = &IdentityMatrix;
}
 
// -------------------------------------------------------------------
 
G4QuadrupoleMagField::G4QuadrupoleMagField(G4double pGradient,
                                           const G4ThreeVector& pOrigin,
                                           G4RotationMatrix* pMatrix)
{
   fGradient = pGradient ;
   fOrigin   = pOrigin ;
   fpMatrix  = pMatrix ;
}
 
// -------------------------------------------------------------------
 
G4Field* G4QuadrupoleMagField::Clone() const
{
   return new G4QuadrupoleMagField(fGradient, fOrigin, fpMatrix);
}
 
// -------------------------------------------------------------------
 
G4QuadrupoleMagField::~G4QuadrupoleMagField() = default;
 
// -------------------------------------------------------------------
 
void G4QuadrupoleMagField::GetFieldValue( const G4double y[],         // [7]
                                                G4double B[]  ) const // [3]
{
  //  with displaced origin and rotation
 
  G4ThreeVector r_global = G4ThreeVector(y[0] - fOrigin.x(),
                                         y[1] - fOrigin.y(),
                                         y[2] - fOrigin.z());
  
  const G4ThreeVector r_local = (*fpMatrix) * r_global;
  const G4ThreeVector B_local( fGradient * r_local.y(),
                               fGradient * r_local.x(), 0);
  const G4ThreeVector B_global = fpMatrix->inverse() * B_local;
 
  B[0] = B_global.x();
  B[1] = B_global.y();
  B[2] = B_global.z();
}