G4HelixImplicitEuler.cc

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//
// G4HelixImplicitEuler implementation
//
//  Helix Implicit Euler:
//        x_1 = x_0 + 1/2 * ( helix(h,t_0,x_0)
//                          + helix(h,t_0+h,x_0+helix(h,t0,x0) ) )
//  Second order solver.
//  Take the current derivative and add it to the current position.
//  Take the output and its derivative. Add the mean of both derivatives
//  to form the final output
//
// Author: W.Wander <wwc@mit.edu>, 03/11/1998
// -------------------------------------------------------------------------
 
#include "G4HelixImplicitEuler.hh"
#include "G4ThreeVector.hh"
 
G4HelixImplicitEuler::G4HelixImplicitEuler(G4Mag_EqRhs *EqRhs)
  : G4MagHelicalStepper(EqRhs)
{
}
 
G4HelixImplicitEuler::~G4HelixImplicitEuler()
{
}
  
void
G4HelixImplicitEuler::DumbStepper( const G4double yIn[],
                                   G4ThreeVector  Bfld,
                                   G4double       h,
                                   G4double       yOut[])
{
  const G4int nvar = 6 ;
  G4double yTemp[6], yTemp2[6];
  G4ThreeVector Bfld_endpoint;
 
  // Step forward like in the explicit euler case
  //
  AdvanceHelix( yIn, Bfld, h, yTemp);
 
  // now obtain the new field value at the new point
  //
  MagFieldEvaluate(yTemp, Bfld_endpoint);      
 
  // and also advance along a helix for this field value
  //
  AdvanceHelix( yIn, Bfld_endpoint, h, yTemp2);
 
  // we take the average
  //
  for( G4int i = 0; i < nvar; ++i )
  {
    yOut[i] = 0.5 * ( yTemp[i] + yTemp2[i] );
  }
 
  // NormaliseTangentVector( yOut );           
}