G4ErrorMag_UsualEqRhs.cc

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00027 // $Id: G4ErrorMag_UsualEqRhs.cc 69786 2013-05-15 09:38:51Z gcosmo $
00028 //
00029 //
00030 // --------------------------------------------------------------------
00031 //      GEANT 4 class implementation file 
00032 // --------------------------------------------------------------------
00033 
00034 #include "G4ErrorMag_UsualEqRhs.hh"
00035 #include "G4ErrorPropagatorData.hh"
00036  
00037 //---------------------------------------------------------------------
00038 
00039 G4ErrorMag_UsualEqRhs::G4ErrorMag_UsualEqRhs( G4MagneticField* MagField )
00040   : G4Mag_UsualEqRhs( MagField )
00041 {
00042 }
00043 
00044 G4ErrorMag_UsualEqRhs::~G4ErrorMag_UsualEqRhs()
00045 {
00046 }
00047 
00048 //---------------------------------------------------------------------
00049 void
00050 G4ErrorMag_UsualEqRhs::EvaluateRhsGivenB( const G4double y[],
00051                                           const G4double B[3],
00052                                                 G4double dydx[] ) const
00053 {
00054 
00055   G4Mag_UsualEqRhs::EvaluateRhsGivenB(y, B, dydx );
00056   
00057   if(G4ErrorPropagatorData::GetErrorPropagatorData()->GetMode()
00058      == G4ErrorMode_PropBackwards)
00059   {
00060     G4double momentum_mag_square = sqr(y[3]) + sqr(y[4]) + sqr(y[5]);
00061     G4double inv_momentum_magnitude = 1.0 / std::sqrt( momentum_mag_square );
00062     
00063     G4double cof = FCof()*inv_momentum_magnitude;
00064 
00065     dydx[3] = cof*(y[4]*(-B[2]) - y[5]*(-B[1])) ;
00066     dydx[4] = cof*(y[5]*(-B[0]) - y[3]*(-B[2])) ;
00067     dydx[5] = cof*(y[3]*(-B[1]) - y[4]*(-B[0])) ;    
00068   }
00069   return;
00070 }

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