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// $Id: G4MonopoleEq.cc,v 1.2 2010/03/18 10:23:29 japost Exp $
// GEANT4 tag $Name: field-V09-03-03 $
//
//
//  This is the right-hand side for equation of motion for a 
//   magnetic charge in a combined Electro-Magnetic field
//
//  d(p_c)/ds=g{c-energyB_ - p_c x E}/pc
//
//  17.11.09   V.Grichine
//
// -------------------------------------------------------------------

#include "G4MonopoleEq.hh"
#include "globals.hh"

void  
G4MonopoleEq::SetChargeMomentumMass(G4double particleCharge, // e+ units
		                            G4double,
                                            G4double particleMass)
{
  fElectroMagCof =  eplus*particleCharge;  // no *c_light as for ususal q
  fElectroMagCof /= 2*fine_structure_const;

  fMassCof = particleMass*particleMass ; 
}



void
G4MonopoleEq::EvaluateRhsGivenB(const G4double y[],
			                const G4double Field[],
				              G4double dydx[] ) const
{

   // Components of y:
   //    0-2 dr/ds, 
   //    3-5 d(pc)/ds - momentum derivatives 

   G4double pSquared = y[3]*y[3] + y[4]*y[4] + y[5]*y[5] ;

   G4double Energy   = std::sqrt( pSquared + fMassCof );
   G4double cof2     = Energy*c_light ;

   G4double pModuleInverse  = 1.0/std::sqrt(pSquared) ;

   //  G4double inverse_velocity = Energy * c_light * pModuleInverse;
   G4double inverse_velocity = Energy * pModuleInverse / c_light;

   G4double cof1     = fElectroMagCof*pModuleInverse ;

   //  G4double vDotE = y[3]*Field[3] + y[4]*Field[4] + y[5]*Field[5] ;

   dydx[0] = y[3]*pModuleInverse ;                         
   dydx[1] = y[4]*pModuleInverse ;                         
   dydx[2] = y[5]*pModuleInverse ;                        

   dydx[3] = cof1*(cof2*Field[0] - (y[4]*Field[5] - y[5]*Field[4])) ;
   
   dydx[4] = cof1*(cof2*Field[1] - (y[5]*Field[3] - y[3]*Field[5])) ; 
 
   dydx[5] = cof1*(cof2*Field[2] - (y[3]*Field[4] - y[4]*Field[3])) ;  

   dydx[6] = 0.;//not used

   // Lab Time of flight
   dydx[7] = inverse_velocity;
   return ;
}