G4HelixMixedStepper.cc

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//
// class G4HelixMixedStepper
//
// Class description:
//
// G4HelixMixedStepper split the Method used for Integration in two:
//
// If Stepping Angle ( h / R_curve) < pi/3  
//        use Stepper for small step(ClassicalRK4 by default)
// Else use  HelixExplicitEuler Stepper
//
// History: 
// Derived from ExactHelicalStepper 18/05/07
//
// -------------------------------------------------------------------------

#include "G4HelixMixedStepper.hh"
#include "G4PhysicalConstants.hh"
#include "G4ClassicalRK4.hh"
#include "G4CashKarpRKF45.hh"
#include "G4SimpleRunge.hh"
#include "G4HelixImplicitEuler.hh"
#include "G4HelixExplicitEuler.hh"
#include "G4HelixSimpleRunge.hh"
#include "G4ExactHelixStepper.hh"
#include "G4ExplicitEuler.hh"
#include "G4ImplicitEuler.hh"
#include "G4SimpleHeum.hh"
#include "G4RKG3_Stepper.hh"
#include "G4NystromRK4.hh"

#include "G4ThreeVector.hh"
#include "G4LineSection.hh"

G4HelixMixedStepper::G4HelixMixedStepper(G4Mag_EqRhs *EqRhs,G4int fStepperNumber, G4double angleThr)
  : G4MagHelicalStepper(EqRhs), fNumCallsRK4(0), fNumCallsHelix(0)
{
   SetVerbose(1);
   if( angleThr < 0.0 ){
     fAngle_threshold= 0.33*pi;
   }else{
     fAngle_threshold= angleThr;
   }

   if(fStepperNumber<0)
     fStepperNumber=4;  // Default is RK4
   fRK4Stepper =  SetupStepper(EqRhs, fStepperNumber);
}

G4HelixMixedStepper::~G4HelixMixedStepper()
{  
  delete(fRK4Stepper);
  if (fVerbose>0){ PrintCalls();};
}

void G4HelixMixedStepper::Stepper(  const G4double  yInput[7],
                               const G4double dydx[7],
                                     G4double Step,
                                     G4double yOut[7],
                                     G4double yErr[])

{
  //Estimation of the Stepping Angle
  
  G4ThreeVector Bfld;
  MagFieldEvaluate(yInput, Bfld);
  
  G4double Bmag = Bfld.mag();
  const G4double *pIn = yInput+3;
  G4ThreeVector initVelocity= G4ThreeVector( pIn[0], pIn[1], pIn[2]);
  G4double      velocityVal = initVelocity.mag();
  G4double R_1;
  G4double Ang_curve;
  
  R_1=std::abs(GetInverseCurve(velocityVal,Bmag));
  Ang_curve=R_1*Step;
  SetAngCurve(Ang_curve);
  SetCurve(std::abs(1/R_1));
  
  if(Ang_curve< fAngle_threshold){
    fNumCallsRK4++;
    fRK4Stepper->Stepper(yInput,dydx,Step,yOut,yErr);
  }
  else
  {
    fNumCallsHelix++;
    const G4int    nvar = 6 ;
    G4int          i;
    G4double       yTemp[7], yIn[7], yTemp2[7];
    G4ThreeVector  Bfld_midpoint;

    //  Saving yInput because yInput and yOut can be aliases for same array
    for(i=0;i<nvar;i++) yIn[i]=yInput[i];
    
    G4double halfS = Step * 0.5;
    // 1. Do first half step and full step
    AdvanceHelix(yIn,   Bfld,          halfS, yTemp, yTemp2); // yTemp2 for s=2*h (halfS)
    //**********

    MagFieldEvaluate(yTemp, Bfld_midpoint) ;

    // 2. Do second half step - with revised field
    // NOTE: Could avoid this call if  'Bfld_midpoint == Bfld' or diff 'almost' zero
    AdvanceHelix(yTemp, Bfld_midpoint, halfS, yOut); // Not requesting y at s=2*h (halfS)
    //**********
    
    // 3. Estimate the integration error - should be (nearly) zero if Bfield= constant
    for(i=0;i<nvar;i++) {
      yErr[i] = yOut[i] - yTemp2[i] ;
    }
  }
}

void
G4HelixMixedStepper::DumbStepper( const G4double  yIn[],
                                   G4ThreeVector   Bfld,
                                   G4double        h,
                                   G4double        yOut[])
{
  AdvanceHelix(yIn, Bfld, h, yOut);
}

G4double G4HelixMixedStepper::DistChord()   const
{
  // Implementation : must check whether h/R > 2 pi  !!
  //   If( h/R <  pi) use G4LineSection::DistLine
  //   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;
}

// ---------------------------------------------------------------------------
void G4HelixMixedStepper::PrintCalls()
{
  G4cout<<"In HelixMixedStepper::Number of calls to smallStepStepper = "<<fNumCallsRK4
        <<"  and Number of calls to Helix = "<<fNumCallsHelix<<G4endl;
}

G4MagIntegratorStepper*
G4HelixMixedStepper::SetupStepper(G4Mag_EqRhs* pE, G4int StepperNumber)
{
  G4MagIntegratorStepper* pStepper;
  if (fVerbose>0)
    G4cout<<"In G4HelixMixedStepper: Choosing Stepper for small steps. Choice is ";
  switch ( StepperNumber )
    {
     case 0:
     case 4: pStepper = new G4ClassicalRK4( pE ); if (fVerbose>0)G4cout<<"G4ClassicalRK4"<<G4endl; break;

     // Steppers with embedded estimation of error
     case 1: pStepper = new G4NystromRK4( pE ); if (fVerbose>0)G4cout<<"G4NystromRK4"<<G4endl; break;
     case 8: pStepper = new G4CashKarpRKF45( pE );    if (fVerbose>0)G4cout<<"G4CashKarpRKF45"<<G4endl; break;
        
     // Lower order RK Steppers - ok overall, good for uneven fields
     case 2: pStepper = new G4SimpleRunge( pE ); if (fVerbose>0)G4cout<<"G4SimpleRunge"<<G4endl; break;
     case 3: pStepper = new G4SimpleHeum( pE );  if (fVerbose>0)G4cout<<"G4SimpleHeum"<<G4endl;break;

     // Helical Steppers - 
     //   Since these are used for long steps, less useful
     case 5: pStepper = new G4HelixExplicitEuler( pE ); if (fVerbose>0)G4cout<<"G4HelixExplicitEuler"<<G4endl; break;
     case 6: pStepper = new G4HelixImplicitEuler( pE ); if (fVerbose>0)G4cout<<"G4HelixImplicitEuler"<<G4endl; break;
     case 7: pStepper = new G4HelixSimpleRunge( pE ); if (fVerbose>0)G4cout<<"G4HelixSimpleRunge"<<G4endl; break;

     // Exact Helix - only for cases of i)uniform field
     //  ii) segmented uniform field (maybe)
     case 9: pStepper = new G4ExactHelixStepper( pE );  if (fVerbose>0)G4cout<<"G4ExactHelixStepper"<<G4endl;   break;

     case 10: pStepper = new G4RKG3_Stepper( pE );  if (fVerbose>0)G4cout<<"G4RKG3_Stepper"<<G4endl;   break;

     // Low Order Steppers - not good except for very weak fields
     case 11: pStepper = new G4ExplicitEuler( pE ); if (fVerbose>0)G4cout<<"G4ExplicitEuler"<<G4endl; break;
     case 12: pStepper = new G4ImplicitEuler( pE ); if (fVerbose>0)G4cout<<"G4ImplicitEuler"<<G4endl; break;
        
     case -1:
     default: pStepper = new G4ClassicalRK4( pE );G4cout<<"G4ClassicalRK4 (Default)."<<G4endl; break;
      
    }
  return pStepper;
}