G4BrentLocator Class Reference

G4BrentLocator implements the calculation of the intersection point with a boundary when G4PropagationInField is used. Second order locator based on Brent Method for finding the intersection point by means of a 'depth' algorithm in case of slow progress (intersection is not found after 100 trials). More...

#include <G4BrentLocator.hh>

Inheritance diagram for G4BrentLocator:

Public Member Functions
	G4BrentLocator (G4Navigator *theNavigator)
	~G4BrentLocator () override
G4bool	EstimateIntersectionPoint (const G4FieldTrack &curveStartPointTangent, const G4FieldTrack &curveEndPointTangent, const G4ThreeVector &trialPoint, G4FieldTrack &intersectPointTangent, G4bool &recalculatedEndPoint, G4double &fPreviousSafety, G4ThreeVector &fPreviousSftOrigin) override
Public Member Functions inherited from G4VIntersectionLocator
	G4VIntersectionLocator (G4Navigator *theNavigator)
virtual	~G4VIntersectionLocator ()
G4bool	IntersectChord (const G4ThreeVector &StartPointA, const G4ThreeVector &EndPointB, G4double &NewSafety, G4double &PreviousSafety, G4ThreeVector &PreviousSftOrigin, G4double &LinearStepLength, G4ThreeVector &IntersectionPoint, G4bool *calledNavigator=nullptr)
void	SetEpsilonStepFor (G4double EpsilonStep)
void	SetDeltaIntersectionFor (G4double deltaIntersection)
void	SetNavigatorFor (G4Navigator *fNavigator)
void	SetChordFinderFor (G4ChordFinder *fCFinder)
void	SetVerboseFor (G4int fVerbose)
G4int	GetVerboseFor ()
G4double	GetDeltaIntersectionFor ()
G4double	GetEpsilonStepFor ()
G4Navigator *	GetNavigatorFor ()
G4ChordFinder *	GetChordFinderFor ()
void	SetSafetyParametersFor (G4bool UseSafety)
void	AdjustIntersections (G4bool UseCorrection)
G4bool	AreIntersectionsAdjusted ()
void	AddAdjustementOfFoundIntersection (G4bool UseCorrection)
G4bool	GetAdjustementOfFoundIntersection ()
void	printStatus (const G4FieldTrack &startFT, const G4FieldTrack &currentFT, G4double requestStep, G4double safety, G4int stepNum)
void	SetCheckMode (G4bool value)
G4bool	GetCheckMode ()

Additional Inherited Members
Static Public Member Functions inherited from G4VIntersectionLocator
static void	printStatus (const G4FieldTrack &startFT, const G4FieldTrack &currentFT, G4double requestStep, G4double safety, G4int stepNum, std::ostream &oss, G4int verboseLevel)
Protected Member Functions inherited from G4VIntersectionLocator
G4FieldTrack	ReEstimateEndpoint (const G4FieldTrack &CurrentStateA, const G4FieldTrack &EstimtdEndStateB, G4double linearDistSq, G4double curveDist)
G4bool	CheckAndReEstimateEndpoint (const G4FieldTrack &CurrentStartA, const G4FieldTrack &EstimatedEndB, G4FieldTrack &RevisedEndPoint, G4int &errorCode)
G4ThreeVector	GetSurfaceNormal (const G4ThreeVector &CurrentInt_Point, G4bool &validNormal)
G4ThreeVector	GetGlobalSurfaceNormal (const G4ThreeVector &CurrentE_Point, G4bool &validNormal)
G4bool	AdjustmentOfFoundIntersection (const G4ThreeVector &A, const G4ThreeVector &CurrentE_Point, const G4ThreeVector &CurrentF_Point, const G4ThreeVector &MomentumDir, const G4bool IntersectAF, G4ThreeVector &IntersectionPoint, G4double &NewSafety, G4double &fPrevSafety, G4ThreeVector &fPrevSftOrigin)
void	ReportTrialStep (G4int step_no, const G4ThreeVector &ChordAB_v, const G4ThreeVector &ChordEF_v, const G4ThreeVector &NewMomentumDir, const G4ThreeVector &NormalAtEntry, G4bool validNormal)
G4bool	LocateGlobalPointWithinVolumeAndCheck (const G4ThreeVector &pos)
void	LocateGlobalPointWithinVolumeCheckAndReport (const G4ThreeVector &pos, const G4String &CodeLocationInfo, G4int CheckMode)
void	ReportReversedPoints (std::ostringstream &ossMsg, const G4FieldTrack &StartPointVel, const G4FieldTrack &EndPointVel, G4double NewSafety, G4double epsStep, const G4FieldTrack &CurrentA_PointVelocity, const G4FieldTrack &CurrentB_PointVelocity, const G4FieldTrack &SubStart_PointVelocity, const G4ThreeVector &CurrentE_Point, const G4FieldTrack &ApproxIntersecPointV, G4int sbstp_no, G4int sbstp_no_p, G4int depth)
void	ReportProgress (std::ostream &oss, const G4FieldTrack &StartPointVel, const G4FieldTrack &EndPointVel, G4int substep_no, const G4FieldTrack &A_PtVel, const G4FieldTrack &B_PtVel, G4double safetyLast, G4int depth=-1)
void	ReportImmediateHit (const char *MethodName, const G4ThreeVector &StartPosition, const G4ThreeVector &TrialPoint, G4double tolerance, unsigned long int numCalls)
Protected Attributes inherited from G4VIntersectionLocator
G4double	kCarTolerance
G4int	fVerboseLevel = 0
G4bool	fUseNormalCorrection = false
G4bool	fCheckMode = false
G4bool	fiUseSafety = false
G4Navigator *	fiNavigator
G4ChordFinder *	fiChordFinder = nullptr
G4double	fiEpsilonStep = -1.0
G4double	fiDeltaIntersection = -1.0
G4Navigator *	fHelpingNavigator
G4TouchableHistory *	fpTouchable = nullptr

Detailed Description

G4BrentLocator implements the calculation of the intersection point with a boundary when G4PropagationInField is used. Second order locator based on Brent Method for finding the intersection point by means of a 'depth' algorithm in case of slow progress (intersection is not found after 100 trials).

Definition at line 49 of file G4BrentLocator.hh.

Constructor & Destructor Documentation

G4BrentLocator()

G4BrentLocator::G4BrentLocator

(

G4Navigator *

theNavigator

)

Constructor and Destructor.

Definition at line 36 of file G4BrentLocator.cc.

  : G4VIntersectionLocator(theNavigator)
{
  // In case of too slow progress in finding Intersection Point
  // intermediates Points on the Track must be stored.
  // Initialise the array of Pointers [max_depth+1] to do this  
  
  G4ThreeVector zeroV(0.0,0.0,0.0);
  for (auto & idepth : ptrInterMedFT)
  {
    idepth = new G4FieldTrack( zeroV, zeroV, 0., 0., 0., 0.);
  }
}

~G4BrentLocator()

G4BrentLocator::~G4BrentLocator ( )

override

Definition at line 50 of file G4BrentLocator.cc.

{
  for (auto & idepth : ptrInterMedFT)
  {
    delete idepth;
  }
}

Member Function Documentation

EstimateIntersectionPoint()

G4bool G4BrentLocator::EstimateIntersectionPoint ( const G4FieldTrack & curveStartPointTangent, const G4FieldTrack & curveEndPointTangent, const G4ThreeVector & trialPoint, G4FieldTrack & intersectPointTangent, G4bool & recalculatedEndPoint, G4double & fPreviousSafety, G4ThreeVector & fPreviousSftOrigin )

overridevirtual

If such an intersection exists, this method calculates the intersection point of the true path of the particle with the surface of the current volume (or of one of its daughters). Should use lateral displacement as measure of convergence.

Note

Changes the safety!

Parameters

[in]	curveStartPointTangent	Start point tangent track.
[in]	curveEndPointTangent	End point tangent track.
[in]	trialPoint	Trial point.
[out]	intersectPointTangent	Intersection point tangent track.
[out]	recalculatedEndPoint	Flagging if end point was recomputed.
[in,out]	fPreviousSafety	Previous safety distance.
[in,out]	fPreviousSftOrigin	Previous safety point origin.

Returns

Whether intersection exists or not.

Implements G4VIntersectionLocator.

Definition at line 91 of file G4BrentLocator.cc.

{   
  // Find Intersection Point ( A, B, E )  of true path AB - start at E.
 
  G4bool found_approximate_intersection = false;
  G4bool there_is_no_intersection       = false;
  
  G4FieldTrack  CurrentA_PointVelocity = CurveStartPointVelocity; 
  G4FieldTrack  CurrentB_PointVelocity = CurveEndPointVelocity;
  G4ThreeVector CurrentE_Point = TrialPoint;
  G4bool        validNormalAtE = false;
  G4ThreeVector NormalAtEntry;
 
  G4FieldTrack  ApproxIntersecPointV(CurveEndPointVelocity); // FT-Def-Construct
  G4double      NewSafety = 0.0;
  G4bool        last_AF_intersection = false; 
 
  // G4bool final_section= true;  // Shows whether current section is last
                                  // (i.e. B=full end)
  G4bool first_section = true;
  recalculatedEndPoint = false; 
 
  G4bool restoredFullEndpoint = false;
 
  G4long oldprc;  // cout, cerr precision
  G4int substep_no = 0;
   
  // Limits for substep number
  //
  const G4int max_substeps=   10000;  // Test 120  (old value 100 )
  const G4int warn_substeps=   1000;  //      100  
 
  // Statistics for substeps
  //
  static G4ThreadLocal G4int max_no_seen= -1; 
 
  // Counter for restarting Bintermed
  //
  G4int restartB = 0;
 
  //--------------------------------------------------------------------------  
  //  Algorithm for the case if progress in founding intersection is too slow.
  //  Process is defined too slow if after N=param_substeps advances on the
  //  path, it will be only 'fraction_done' of the total length.
  //  In this case the remaining length is divided in two half and 
  //  the loop is restarted for each half.  
  //  If progress is still too slow, the division in two halfs continue
  //  until 'max_depth'.
  //--------------------------------------------------------------------------
 
  const G4int param_substeps = 50; // Test value for the maximum number
                                   // of substeps
  const G4double fraction_done = 0.3;
 
  G4bool Second_half = false;     // First half or second half of divided step
 
  NormalAtEntry = GetSurfaceNormal(CurrentE_Point, validNormalAtE); 
 
  // We need to know this for the 'final_section':
  // real 'final_section' or first half 'final_section'
  // In algorithm it is considered that the 'Second_half' is true
  // and it becomes false only if we are in the first-half of level
  // depthness or if we are in the first section
 
  G4int depth = 0; // Depth counts how many subdivisions of initial step made
 
#ifdef G4DEBUG_FIELD
  const G4double tolerance = 1.0e-8; 
  G4ThreeVector  StartPosition = CurveStartPointVelocity.GetPosition(); 
  if( (TrialPoint - StartPosition).mag() < tolerance * CLHEP::mm ) 
  {
     G4Exception("G4BrentLocator::EstimateIntersectionPoint()", 
                 "GeomNav1002", JustWarning,
                 "Intersection point F is exactly at start point A." ); 
  }
#endif
 
  // Intermediates Points on the Track = Subdivided Points must be stored.
  // Give the initial values to 'InterMedFt'
  // Important is 'ptrInterMedFT[0]', it saves the 'EndCurvePoint'
  //
  *ptrInterMedFT[0] = CurveEndPointVelocity;
  for (auto idepth=1; idepth<max_depth+1; ++idepth )
  {
    *ptrInterMedFT[idepth] = CurveStartPointVelocity;
  }
 
  //Final_section boolean store
  G4bool fin_section_depth[max_depth];
  for (bool & idepth : fin_section_depth)
  {
    idepth = true;
  }
 
  // 'SubStartPoint' is needed to calculate the length of the divided step
  //
  G4FieldTrack SubStart_PointVelocity = CurveStartPointVelocity;
   
  do   // Loop checking, 07.10.2016, J.Apostolakis
  {
    G4int substep_no_p = 0;
    G4bool sub_final_section = false; // the same as final_section,
                                      // but for 'sub_section'
    SubStart_PointVelocity = CurrentA_PointVelocity;
 
    do   // Loop checking, 07.10.2016, J.Apostolakis
    { // REPEAT param 
      G4ThreeVector Point_A = CurrentA_PointVelocity.GetPosition();  
      G4ThreeVector Point_B = CurrentB_PointVelocity.GetPosition();
       
      // F = a point on true AB path close to point E 
      // (the closest if possible)
      //
      if(substep_no_p==0)
      {
        ApproxIntersecPointV = GetChordFinderFor()
                               ->ApproxCurvePointV( CurrentA_PointVelocity, 
                                                    CurrentB_PointVelocity, 
                                                    CurrentE_Point,
                                                    GetEpsilonStepFor());
          //  The above method is the key & most intuitive part ...
      }
#ifdef G4DEBUG_FIELD
      if( ApproxIntersecPointV.GetCurveLength() > 
          CurrentB_PointVelocity.GetCurveLength() * (1.0 + tolerance) )
      {
        G4Exception("G4BrentLocator::EstimateIntersectionPoint()", 
                    "GeomNav0003", FatalException,
                    "Intermediate F point is past end B point" ); 
      }
#endif
 
      G4ThreeVector CurrentF_Point = ApproxIntersecPointV.GetPosition();
 
      // First check whether EF is small - then F is a good approx. point 
      // Calculate the length and direction of the chord AF
      //
      G4ThreeVector  ChordEF_Vector = CurrentF_Point - CurrentE_Point;
      G4ThreeVector  NewMomentumDir = ApproxIntersecPointV.GetMomentumDir(); 
      G4double       MomDir_dot_Norm = NewMomentumDir.dot( NormalAtEntry ) ;
     
#ifdef G4DEBUG_FIELD
      G4ThreeVector  ChordAB = Point_B - Point_A;
 
      G4VIntersectionLocator::ReportTrialStep( substep_no, ChordAB,
               ChordEF_Vector, NewMomentumDir, NormalAtEntry, validNormalAtE ); 
#endif
 
      G4bool adequate_angle;
      adequate_angle =  ( MomDir_dot_Norm >= 0.0 ) // Can use -epsilon instead.
                    || (! validNormalAtE );        //  Makes criterion invalid
      G4double EF_dist2 = ChordEF_Vector.mag2();
      if ( ( EF_dist2 <= sqr(fiDeltaIntersection) && ( adequate_angle ) )
        || ( EF_dist2 <= kCarTolerance*kCarTolerance ) )
      {
        found_approximate_intersection = true;
    
        // Create the "point" return value
        //
        IntersectedOrRecalculatedFT = ApproxIntersecPointV;
        IntersectedOrRecalculatedFT.SetPosition( CurrentE_Point );
        
        if ( GetAdjustementOfFoundIntersection() )
        {
          // Try to Get Correction of IntersectionPoint using SurfaceNormal()
          //  
          G4ThreeVector IP;
          G4ThreeVector MomentumDir=ApproxIntersecPointV.GetMomentumDirection();
          G4bool goodCorrection = AdjustmentOfFoundIntersection( Point_A,
                                    CurrentE_Point, CurrentF_Point, MomentumDir,
                                    last_AF_intersection, IP, NewSafety,
                                    fPreviousSafety, fPreviousSftOrigin );
          if ( goodCorrection )
          {
            IntersectedOrRecalculatedFT = ApproxIntersecPointV;
            IntersectedOrRecalculatedFT.SetPosition(IP);
          }
        }
       
        // Note: in order to return a point on the boundary, 
        //       we must return E. But it is F on the curve.
        //       So we must "cheat": we are using the position at point E
        //       and the velocity at point F !!!
        //
        // This must limit the length we can allow for displacement!
      }
      else  // E is NOT close enough to the curve (ie point F)
      {
        // Check whether any volumes are encountered by the chord AF
        // ---------------------------------------------------------
        // First relocate to restore any Voxel etc information
        // in the Navigator before calling ComputeStep()
        //
        GetNavigatorFor()->LocateGlobalPointWithinVolume( Point_A );
 
        G4ThreeVector PointG;   // Candidate intersection point
        G4double stepLengthAF; 
        G4bool usedNavigatorAF = false; 
        G4bool Intersects_AF = IntersectChord( Point_A,   CurrentF_Point,
                                               NewSafety,fPreviousSafety,
                                               fPreviousSftOrigin,
                                               stepLengthAF,
                                               PointG,
                                               &usedNavigatorAF);
        last_AF_intersection = Intersects_AF;
        if( Intersects_AF )
        {
          // G is our new Candidate for the intersection point.
          // It replaces  "E" and we will repeat the test to see if
          // it is a good enough approximate point for us.
          //       B    <- F
          //       E    <- G
          //
          G4FieldTrack EndPoint = ApproxIntersecPointV;
          ApproxIntersecPointV = GetChordFinderFor()->ApproxCurvePointS(
                                 CurrentA_PointVelocity, CurrentB_PointVelocity,
                                 EndPoint,CurrentE_Point, CurrentF_Point,PointG,
                                 true, GetEpsilonStepFor() );
          CurrentB_PointVelocity = EndPoint;
          CurrentE_Point = PointG;
 
          // Need to recalculate the Exit Normal at the new PointG 
          // Know that a call was made to Navigator::ComputeStep in
          // IntersectChord above.
          //
          G4bool validNormalLast; 
          NormalAtEntry  = GetSurfaceNormal( PointG, validNormalLast ); 
          validNormalAtE = validNormalLast; 
            
          // By moving point B, must take care if current
          // AF has no intersection to try current FB!!
          //
          fin_section_depth[depth] = false;
#ifdef G4VERBOSE
          if( fVerboseLevel > 3 )
          {
            G4cout << "G4PiF::LI> Investigating intermediate point"
                   << " at s=" << ApproxIntersecPointV.GetCurveLength()
                   << " on way to full s="
                   << CurveEndPointVelocity.GetCurveLength() << G4endl;
          }
#endif
        }
        else  // not Intersects_AF
        {  
          // In this case:
          // There is NO intersection of AF with a volume boundary.
          // We must continue the search in the segment FB!
          //
          GetNavigatorFor()->LocateGlobalPointWithinVolume( CurrentF_Point );
 
          G4double stepLengthFB;
          G4ThreeVector PointH;
          G4bool usedNavigatorFB = false; 
 
          // Check whether any volumes are encountered by the chord FB
          // ---------------------------------------------------------
 
          G4bool Intersects_FB = IntersectChord( CurrentF_Point, Point_B, 
                                                 NewSafety,fPreviousSafety,
                                                 fPreviousSftOrigin,
                                                 stepLengthFB,
                                                 PointH,
                                                 &usedNavigatorFB);
          if( Intersects_FB )
          { 
            // There is an intersection of FB with a volume boundary
            // H <- First Intersection of Chord FB 
 
            // H is our new Candidate for the intersection point.
            // It replaces  "E" and we will repeat the test to see if
            // it is a good enough approximate point for us.
 
            // Note that F must be in volume volA  (the same as A)
            // (otherwise AF would meet a volume boundary!)
            //   A    <- F 
            //   E    <- H
            //
            G4FieldTrack InterMed = ApproxIntersecPointV;
            ApproxIntersecPointV = GetChordFinderFor()->ApproxCurvePointS(
                          CurrentA_PointVelocity,CurrentB_PointVelocity,
                          InterMed,CurrentE_Point,CurrentF_Point,PointH,
                          false,GetEpsilonStepFor());
            CurrentA_PointVelocity = InterMed;
            CurrentE_Point = PointH;
 
            // Need to recalculate the Exit Normal at the new PointG
            //
            G4bool validNormalLast; 
            NormalAtEntry = GetSurfaceNormal( PointH, validNormalLast ); 
            validNormalAtE = validNormalLast;
          }
          else  // not Intersects_FB
          {
            // There is NO intersection of FB with a volume boundary
 
            if( fin_section_depth[depth]  )
            { 
              // If B is the original endpoint, this means that whatever
              // volume(s) intersected the original chord, none touch the
              // smaller chords we have used.
              // The value of 'IntersectedOrRecalculatedFT' returned is
              // likely not valid 
 
              // Check on real final_section or SubEndSection
              //
              if( ((Second_half)&&(depth==0)) || (first_section) )
              {
                there_is_no_intersection = true;   // real final_section
              }
              else
              {
                // end of subsection, not real final section 
                // exit from the and go to the depth-1 level 
 
                substep_no_p = param_substeps+2;  // exit from the loop
 
                // but 'Second_half' is still true because we need to find
                // the 'CurrentE_point' for the next loop
                //
                Second_half = true; 
                sub_final_section = true;
              }
            }
            else
            {
              if( depth==0 )
              {
                // We must restore the original endpoint
                //
                CurrentA_PointVelocity = CurrentB_PointVelocity;  // Got to B
                CurrentB_PointVelocity = CurveEndPointVelocity;
                SubStart_PointVelocity = CurrentA_PointVelocity;
                ApproxIntersecPointV = GetChordFinderFor()
                               ->ApproxCurvePointV( CurrentA_PointVelocity, 
                                                    CurrentB_PointVelocity, 
                                                    CurrentE_Point,
                                                    GetEpsilonStepFor());
 
                restoredFullEndpoint = true;
                ++restartB; // counter
              }
              else
              {
                // We must restore the depth endpoint
                //
                CurrentA_PointVelocity = CurrentB_PointVelocity;  // Got to B
                CurrentB_PointVelocity =  *ptrInterMedFT[depth];
                SubStart_PointVelocity = CurrentA_PointVelocity;
                ApproxIntersecPointV = GetChordFinderFor()
                               ->ApproxCurvePointV( CurrentA_PointVelocity, 
                                                    CurrentB_PointVelocity, 
                                                    CurrentE_Point,
                                                    GetEpsilonStepFor());
                restoredFullEndpoint = true;
                ++restartB; // counter
              }
            }
          } // Endif (Intersects_FB)
        } // Endif (Intersects_AF)
 
        // Ensure that the new endpoints are not further apart in space
        // than on the curve due to different errors in the integration
        //
        G4double linDistSq, curveDist; 
        linDistSq = ( CurrentB_PointVelocity.GetPosition() 
                    - CurrentA_PointVelocity.GetPosition() ).mag2(); 
        curveDist = CurrentB_PointVelocity.GetCurveLength()
                    - CurrentA_PointVelocity.GetCurveLength();
 
        // Change this condition for very strict parameters of propagation 
        //
        if( curveDist*curveDist*(1+2* GetEpsilonStepFor()) < linDistSq )
        {
          // Re-integrate to obtain a new B
          //
          G4FieldTrack newEndPointFT=
                  ReEstimateEndpoint( CurrentA_PointVelocity,
                                      CurrentB_PointVelocity,
                                      linDistSq,    // to avoid recalculation
                                      curveDist );
          G4FieldTrack oldPointVelB = CurrentB_PointVelocity; 
          CurrentB_PointVelocity = newEndPointFT;
         
          if ( (fin_section_depth[depth])           // real final section
             &&( first_section  || ((Second_half)&&(depth==0)) ) )
          {
            recalculatedEndPoint = true;
            IntersectedOrRecalculatedFT = newEndPointFT;
              // So that we can return it, if it is the endpoint!
          }
        }
        if( curveDist < 0.0 )
        {
          fVerboseLevel = 5; // Print out a maximum of information
          printStatus( CurrentA_PointVelocity,  CurrentB_PointVelocity,
                       -1.0, NewSafety,  substep_no );
          std::ostringstream message;
          message << "Error in advancing propagation." << G4endl
                  << "        Error in advancing propagation." << G4endl
                  << "        Point A (start) is " << CurrentA_PointVelocity
                  << G4endl
                  << "        Point B (end)   is " << CurrentB_PointVelocity
                  << G4endl
                  << "        Curve distance is " << curveDist << G4endl
                  << G4endl
                  << "The final curve point is not further along"
                  << " than the original!" << G4endl;
 
          if( recalculatedEndPoint )
          {
            message << "Recalculation of EndPoint was called with fEpsStep= "
                    << GetEpsilonStepFor() << G4endl;
          }
          oldprc = G4cerr.precision(20);
          message << " Point A (Curve start)     is " << CurveStartPointVelocity
                  << G4endl
                  << " Point B (Curve   end)     is " << CurveEndPointVelocity
                  << G4endl
                  << " Point A (Current start)   is " << CurrentA_PointVelocity
                  << G4endl
                  << " Point B (Current end)     is " << CurrentB_PointVelocity
                  << G4endl
                  << " Point S (Sub start)       is " << SubStart_PointVelocity
                  << G4endl
                  << " Point E (Trial Point)     is " << CurrentE_Point
                  << G4endl
                  << " Old Point F(Intersection) is " << CurrentF_Point
                  << G4endl
                  << " New Point F(Intersection) is " << ApproxIntersecPointV
                  << G4endl
                  << "        LocateIntersection parameters are : Substep no= "
                  << substep_no << G4endl
                  << "        Substep depth no= "<< substep_no_p  << " Depth= "
                  << depth << G4endl
                  << "        Restarted no= "<< restartB  << " Epsilon= "
                  << GetEpsilonStepFor() <<" DeltaInters= "
                  << GetDeltaIntersectionFor();
          G4cerr.precision( oldprc ); 
 
          G4Exception("G4BrentLocator::EstimateIntersectionPoint()",
                      "GeomNav0003", FatalException, message);
        }
 
        if( restoredFullEndpoint )
        {
          fin_section_depth[depth] = restoredFullEndpoint;
          restoredFullEndpoint = false;
        }
      } // EndIf ( E is close enough to the curve, ie point F. )
        // tests ChordAF_Vector.mag() <= maximum_lateral_displacement 
 
#ifdef G4DEBUG_LOCATE_INTERSECTION  
      G4int trigger_substepno_print= warn_substeps - 20 ;
 
      if( substep_no >= trigger_substepno_print )
      {
        G4cout << "Difficulty in converging in "
               << "G4BrentLocator::EstimateIntersectionPoint()"
               << G4endl
               << "    Substep no = " << substep_no << G4endl;
        if( substep_no == trigger_substepno_print )
        {
          printStatus( CurveStartPointVelocity, CurveEndPointVelocity,
                       -1.0, NewSafety, 0);
        }
        G4cout << " State of point A: "; 
        printStatus( CurrentA_PointVelocity, CurrentA_PointVelocity,
                     -1.0, NewSafety, substep_no-1, 0);
        G4cout << " State of point B: "; 
        printStatus( CurrentA_PointVelocity, CurrentB_PointVelocity,
                     -1.0, NewSafety, substep_no);
      }
#endif
      ++substep_no; 
      ++substep_no_p;
 
    } while (  ( ! found_approximate_intersection )
            && ( ! there_is_no_intersection )     
            && ( substep_no_p <= param_substeps) );  // UNTIL found or
                                                     // failed param substep
    first_section = false;
 
    if( (!found_approximate_intersection) && (!there_is_no_intersection) )
    {
      G4double did_len = std::abs( CurrentA_PointVelocity.GetCurveLength()
                       - SubStart_PointVelocity.GetCurveLength()); 
      G4double all_len = std::abs( CurrentB_PointVelocity.GetCurveLength()
                       - SubStart_PointVelocity.GetCurveLength());
   
      G4double stepLengthAB;
      G4ThreeVector PointGe;
 
      // Check if progress is too slow and if it possible to go deeper,
      // then halve the step if so
      //
      if ( ( did_len < fraction_done*all_len )
        && (depth < max_depth) && (!sub_final_section) )
      {
        Second_half=false;
        ++depth;
 
        G4double Sub_len = (all_len-did_len)/(2.);
        G4FieldTrack start = CurrentA_PointVelocity;
        auto integrDriver =
                         GetChordFinderFor()->GetIntegrationDriver();
        integrDriver->AccurateAdvance(start, Sub_len, GetEpsilonStepFor());
        *ptrInterMedFT[depth] = start;
        CurrentB_PointVelocity = *ptrInterMedFT[depth];
 
        // Adjust 'SubStartPoint' to calculate the 'did_length' in next loop
        //
        SubStart_PointVelocity = CurrentA_PointVelocity;
 
        // Find new trial intersection point needed at start of the loop
        //
        G4ThreeVector Point_A = CurrentA_PointVelocity.GetPosition();
        G4ThreeVector SubE_point = CurrentB_PointVelocity.GetPosition();   
     
        GetNavigatorFor()->LocateGlobalPointWithinVolume(Point_A);
        G4bool Intersects_AB = IntersectChord(Point_A, SubE_point,
                                              NewSafety, fPreviousSafety,
                                              fPreviousSftOrigin,stepLengthAB,
                                              PointGe);
        if( Intersects_AB )
        {
          last_AF_intersection = Intersects_AB;
          CurrentE_Point = PointGe;
          fin_section_depth[depth] = true;
 
          // Need to recalculate the Exit Normal at the new PointG
          //
          G4bool validNormalAB; 
          NormalAtEntry = GetSurfaceNormal( PointGe, validNormalAB ); 
          validNormalAtE = validNormalAB;  
        }
        else
        {
          // No intersection found for first part of curve
          // (CurrentA,InterMedPoint[depth]). Go to the second part
          //
          Second_half = true;
        }
      } // if did_len
 
      if( (Second_half)&&(depth!=0) )
      {
        // Second part of curve (InterMed[depth],Intermed[depth-1])                       ) 
        // On the depth-1 level normally we are on the 'second_half'
 
        Second_half = true;
 
        //  Find new trial intersection point needed at start of the loop
        //
        SubStart_PointVelocity = *ptrInterMedFT[depth];
        CurrentA_PointVelocity = *ptrInterMedFT[depth];
        CurrentB_PointVelocity = *ptrInterMedFT[depth-1];
         // Ensure that the new endpoints are not further apart in space
        // than on the curve due to different errors in the integration
        //
        G4double linDistSq, curveDist; 
        linDistSq = ( CurrentB_PointVelocity.GetPosition() 
                    - CurrentA_PointVelocity.GetPosition() ).mag2(); 
        curveDist = CurrentB_PointVelocity.GetCurveLength()
                    - CurrentA_PointVelocity.GetCurveLength();
        if( curveDist*curveDist*(1+2*GetEpsilonStepFor() ) < linDistSq )
        {
          // Re-integrate to obtain a new B
          //
          G4FieldTrack newEndPointFT =
                  ReEstimateEndpoint( CurrentA_PointVelocity,
                                      CurrentB_PointVelocity,
                                      linDistSq,    // to avoid recalculation
                                      curveDist );
          G4FieldTrack oldPointVelB = CurrentB_PointVelocity; 
          CurrentB_PointVelocity = newEndPointFT;
          if ( depth==1 )
          {
            recalculatedEndPoint = true;
            IntersectedOrRecalculatedFT = newEndPointFT;
            // So that we can return it, if it is the endpoint!
          }
        }
 
 
        G4ThreeVector Point_A    = CurrentA_PointVelocity.GetPosition();
        G4ThreeVector SubE_point = CurrentB_PointVelocity.GetPosition();   
        GetNavigatorFor()->LocateGlobalPointWithinVolume(Point_A);
        G4bool Intersects_AB = IntersectChord(Point_A, SubE_point, NewSafety,
                                              fPreviousSafety,
                                               fPreviousSftOrigin,stepLengthAB, PointGe);
        if( Intersects_AB )
        {
          last_AF_intersection = Intersects_AB;
          CurrentE_Point = PointGe;
 
          G4bool validNormalAB; 
          NormalAtEntry  = GetSurfaceNormal( PointGe, validNormalAB ); 
          validNormalAtE = validNormalAB;
        }
       
        depth--;
        fin_section_depth[depth]=true;
      }
    }  // if(!found_aproximate_intersection)
 
  } while ( ( ! found_approximate_intersection )
            && ( ! there_is_no_intersection )     
            && ( substep_no <= max_substeps) ); // UNTIL found or failed
 
  if( substep_no > max_no_seen )
  {
    max_no_seen = substep_no; 
#ifdef G4DEBUG_LOCATE_INTERSECTION
    if( max_no_seen > warn_substeps )
    {
      trigger_substepno_print = max_no_seen-20; // Want to see last 20 steps 
    }
#endif
  }
 
  if(  ( substep_no >= max_substeps)
      && !there_is_no_intersection
      && !found_approximate_intersection )
  {
    G4cout << "ERROR - G4BrentLocator::EstimateIntersectionPoint()" << G4endl
           << "        Start and end-point of requested Step:" << G4endl;
    printStatus( CurveStartPointVelocity, CurveEndPointVelocity,
                 -1.0, NewSafety, 0);
    G4cout << "        Start and end-point of current Sub-Step:" << G4endl;
    printStatus( CurrentA_PointVelocity, CurrentA_PointVelocity,
                 -1.0, NewSafety, substep_no-1);
    printStatus( CurrentA_PointVelocity, CurrentB_PointVelocity,
                 -1.0, NewSafety, substep_no);
    std::ostringstream message;
    message << "Too many substeps!" << G4endl
            << "          Convergence is requiring too many substeps: "
            << substep_no << G4endl
            << "          Abandoning effort to intersect. " << G4endl
            << "          Found intersection = "
            << found_approximate_intersection << G4endl
            << "          Intersection exists = "
            << !there_is_no_intersection << G4endl;
    oldprc = G4cout.precision( 10 ); 
    G4double done_len = CurrentA_PointVelocity.GetCurveLength(); 
    G4double full_len = CurveEndPointVelocity.GetCurveLength();
    message << "        Undertaken only length: " << done_len
            << " out of " << full_len << " required." << G4endl
            << "        Remaining length = " << full_len - done_len; 
    G4cout.precision( oldprc ); 
 
    G4Exception("G4BrentLocator::EstimateIntersectionPoint()",
                "GeomNav0003", FatalException, message);
  }
  else if( substep_no >= warn_substeps )
  {  
    oldprc = G4cout.precision( 10 ); 
    std::ostringstream message;
    message << "Many substeps while trying to locate intersection."
            << G4endl
            << "          Undertaken length: "  
            << CurrentB_PointVelocity.GetCurveLength()
            << " - Needed: "  << substep_no << " substeps." << G4endl
            << "          Warning level = " << warn_substeps
            << " and maximum substeps = " << max_substeps;
    G4Exception("G4BrentLocator::EstimateIntersectionPoint()",
                "GeomNav1002", JustWarning, message);
    G4cout.precision( oldprc ); 
  }
  return  !there_is_no_intersection; //  Success or failure
}

---

The documentation for this class was generated from the following files:

• G4BrentLocator.hh
• G4BrentLocator.cc