G4ExactHelixStepper.cc

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//
// G4ExactHelixStepper implementation
//
// Author: J.Apostolakis, 28.01.2005.
//         Implementation adapted from ExplicitEuler by W.Wander 
// -------------------------------------------------------------------

#include "G4ExactHelixStepper.hh"
#include "G4PhysicalConstants.hh"
#include "G4ThreeVector.hh"
#include "G4LineSection.hh"

G4ExactHelixStepper::G4ExactHelixStepper(G4Mag_EqRhs* EqRhs)
  : G4MagHelicalStepper(EqRhs),
    fBfieldValue(DBL_MAX, DBL_MAX, DBL_MAX)
{
}

G4ExactHelixStepper::~G4ExactHelixStepper()
{
} 

// ---------------------------------------------------------------------------

void
G4ExactHelixStepper::Stepper( const G4double yInput[],
                              const G4double*,
                                    G4double hstep,
                                    G4double yOut[],
                                    G4double yErr[] )
{  
  const G4int nvar = 6;

  G4int i;
  G4ThreeVector Bfld_value;

  MagFieldEvaluate(yInput, Bfld_value);        
  AdvanceHelix(yInput, Bfld_value, hstep, yOut);

  // We are assuming a constant field: helix is exact
  //
  for(i=0; i<nvar; ++i)
  {
    yErr[i] = 0.0 ;
  }

  fBfieldValue = Bfld_value;
}

// ---------------------------------------------------------------------------

void
G4ExactHelixStepper::DumbStepper( const G4double yIn[],
                                        G4ThreeVector Bfld,
                                        G4double h,
                                        G4double yOut[])
{
  // Assuming a constant field: solution is a helix

  AdvanceHelix(yIn, Bfld, h, yOut);

  G4Exception("G4ExactHelixStepper::DumbStepper",
              "GeomField0002", FatalException,
              "Should not be called. Stepper must do all the work." ); 
}  


// ---------------------------------------------------------------------------

G4double
G4ExactHelixStepper::DistChord() const 
{
  // Implementation : must check whether h/R >  pi  !!
  //   If( h/R <  pi)   DistChord=h/2*std::tan(Ang_curve/4)
  //   Else             DistChord=R_helix

  G4double distChord;
  G4double Ang_curve=GetAngCurve();

  if (Ang_curve<=pi)
  {
    distChord=GetRadHelix()*(1-std::cos(0.5*Ang_curve));
  }
  else if(Ang_curve<twopi)
  {
    distChord=GetRadHelix()*(1+std::cos(0.5*(twopi-Ang_curve)));
  }
  else
  {
    distChord=2.*GetRadHelix();  
  }

  return distChord;
}   

// ---------------------------------------------------------------------------

G4int
G4ExactHelixStepper::IntegratorOrder() const 
{
  return 1; 
}