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 //
 // G4FieldManager
 //
 // Class description:
 //
 // A class to manage (Store) a pointer to the Field subclass that
 // describes the field of a detector (magnetic, electric or other).
 // Also stores a reference to the chord finder.
 //
 // The G4FieldManager class exists to allow the user program to specify 
 // the electric, magnetic and/or other field(s) of the detector.
 // 
 // A field manager can be set to a logical volume (or to more than one), 
 // in order to vary its field from that of the world.  In this manner
 // a zero or constant field can override a global field,  a more or 
 // less exact version can override the external approximation, lower
 // or higher precision for tracking can be specified, a different 
 // stepper can be chosen for different volumes, ...
 //
 // It also stores a pointer to the ChordFinder object that can do the
 // propagation in this field. All geometrical track "advancement" 
 // in the field is handled by this ChordFinder object.
 //
 // G4FieldManager allows the other classes/object (of the MagneticField 
 // & other class categories) to find out whether a detector field object 
 // exists and what that object is.
 //
 // The Chord Finder must be created either by calling CreateChordFinder
 // for a Magnetic Field or by the user creating a  a Chord Finder object
 // "manually" and setting this pointer.
 //
 // A default FieldManager is created by the singleton class
 // G4NavigatorForTracking and exists before main is called.
 // However a new one can be created and given to G4NavigatorForTracking.
 //
 // Our current design envisions that one Field manager is 
 // valid for each region detector.
 //
 // It is expected that a particular geometrical region has a Field manager.
 // By default a Field Manager is created for the world volume, and
 // will be utilised for all volumes unless it is overridden by a 'local'
 // field manager.
 // Note also that a region with both electric E and magnetic B field will 
 // have these treated as one field.
 // Similarly it could be extended to treat other fields as additional
 // components of a single field type.
 
 // Author: John Apostolakis, 10.03.97 - design and implementation
 // -------------------------------------------------------------------
 #ifndef G4FIELDMANAGER_HH
 #define G4FIELDMANAGER_HH 1
 
 #include "globals.hh"
 
 class G4Field;
 class G4MagneticField;
 class G4ChordFinder;
 class G4Track;  // Forward reference for parameter configuration
 
 class G4FieldManager
 {
   public:  // with description
 
     G4FieldManager(G4Field* detectorField = nullptr, 
                    G4ChordFinder* pChordFinder = nullptr, 
                    G4bool b = true ); // fieldChangesEnergy is taken from field
       // General constructor for any field.
       // -> Must be set with field and chordfinder for use.
     G4FieldManager(G4MagneticField* detectorMagneticField);
       // Creates ChordFinder
       // -> Assumes pure magnetic field (so energy constant)
 
     virtual ~G4FieldManager();
 
     G4FieldManager(const G4FieldManager&) = delete;
     G4FieldManager& operator=(const G4FieldManager&) = delete;
 
     G4bool SetDetectorField(G4Field* detectorField, G4int failMode = 0);
       // Pushes the field to the equation.
       // Failure to push the field (due to absence of a chord finder, driver,
       // stepper or equation) is
       //      - '0' = quiet      : Do not complain if chordFinder == 0
       //                            (It will still warn for other error.)
       //      - '1' = warn       : a warning if anything is missing
       //      - '2'/else = FATAL : a fatal error for all other values.
       // Returns success (true) or failure (false)
 
     inline void ProposeDetectorField(G4Field* detectorField);
       // Pushes the field to this class only -- no further.
       // Should be used  to initialise this field, only *before* creating
       // the chord finder and its dependent classes.
       // User is then responsible to ensure that:
       //     i) an equation, stepper, driver and chord finder are created
       //    ii) this field is used by the equation.
 
     inline void  ChangeDetectorField(G4Field* detectorField);    
       // Pushes the field to the equation ( & keeps its address )
       // Can be used only once the equation, stepper, driver and chord finder
       // have all been created.  Else it is an error.
         
     inline const G4Field*  GetDetectorField() const;
     inline G4bool          DoesFieldExist() const;
       // Set, get and check the field object
 
     void CreateChordFinder(G4MagneticField* detectorMagField);
     inline void SetChordFinder(G4ChordFinder* aChordFinder);
     inline G4ChordFinder* GetChordFinder();
     inline const G4ChordFinder* GetChordFinder() const;
       // Create, set or get the associated Chord Finder
 
     virtual void   ConfigureForTrack( const G4Track * ); 
       // Setup the choice of the configurable parameters 
       // relying on the current track's energy, particle identity, ..
       // Note: in addition to the values of member variables, 
       //       a user can use this to change the ChordFinder, the field, ...
 
   public:  // with description
    
     inline G4double GetDeltaIntersection() const;
       // Accuracy for boundary intersection.
 
     inline G4double GetDeltaOneStep() const;
       // Accuracy for one tracking/physics step.
 
     inline void SetAccuraciesWithDeltaOneStep(G4double valDeltaOneStep); 
       // Sets both accuracies, maintaining a fixed ratio for accuracies 
       // of volume Intersection and Integration (in One Step) 
 
     inline void     SetDeltaOneStep(G4double valueD1step); 
       // Set accuracy for integration of one step.   (only)
     inline void     SetDeltaIntersection(G4double valueDintersection); 
       // Set accuracy of  intersection of a volume.  (only)
 
     inline G4double  GetMinimumEpsilonStep() const;
     G4bool           SetMinimumEpsilonStep( G4double newEpsMin );
       // Minimum for Relative accuracy of a Step 
 
     inline G4double  GetMaximumEpsilonStep() const;
     G4bool           SetMaximumEpsilonStep( G4double newEpsMax );
       // Maximum for Relative accuracy of a Step 
  
     inline G4bool   DoesFieldChangeEnergy() const;
     inline void     SetFieldChangesEnergy(G4bool value);
       // For electric field this should be true
       // For magnetic field this should be false
     
     virtual G4FieldManager* Clone() const;
       // Needed for multi-threading, create a clone of this object
 
   public:
     static G4double GetMaxAcceptedEpsilon();
     static G4bool   SetMaxAcceptedEpsilon(G4double maxEps, G4bool softFail= false);
      // Set value -- within limits.
      // If it fails, with softFail=true it gives Warning, else FatalException
    
   protected:
     static G4double fMaxAcceptedEpsilon;
     static constexpr G4double fMinAcceptedEpsilon= 1000.0 * std::numeric_limits<G4double>::epsilon();
       // Epsilon_min/max values must be smaller than this - for robust integration
 
     static constexpr G4double fMaxWarningEpsilon= 0.001; // Setting larger value will give warning.
     static constexpr G4double fMaxFinalEpsilon=   0.02;  // Will not accept larger values
    
     static G4bool             fVerboseConstruction;
       // Control verbosity of constructors
 
   private:
 
     void InitialiseFieldChangesEnergy();
       // Check whether field/equation change the energy,
       // and sets the data member accordingly
       // Note: does not handle special cases - this must be done
       // separately  (e.g. magnetic monopole in B field )
   
   protected:
      void ReportBadEpsilonValue(G4ExceptionDescription& erm, G4double value,
                                 G4String& name) const;
   
   private:
 
     G4Field* fDetectorField = nullptr;
     G4ChordFinder* fChordFinder = nullptr;
       // Dependent objects -- with state that depends on tracking
 
     G4bool fAllocatedChordFinder = false; // Did we used "new" to
                                           // create fChordFinder ?
     // INVARIANTS of tracking  ---------------------------------------
     // 
     //  1. 'CONSTANTS' - default values for accuracy parameters
     //
     const G4double fEpsilonMinDefault= 5.0e-5; // Expected: 5.0e-5 to 1.0e-10 ...
     const G4double fEpsilonMaxDefault= 1.0e-3; // Expected: 1.0e-3 to 1.0e-8 ...
 
     static G4double fDefault_Delta_One_Step_Value;   // = 0.01 *  millimeter;
     static G4double fDefault_Delta_Intersection_Val; // = 0.001 * millimeter;
       // Default values for accuracy parameters
 
     //  2. CHARACTERISTIC of field
     //
     G4bool fFieldChangesEnergy = false;
 
     //  3. PARAMETERS that determine the accuracy of integration or intersection
     //
     G4double fDelta_One_Step_Value;      //  for one tracking/physics step
     G4double fDelta_Intersection_Val;    //  for boundary intersection
       // Values for the required accuracies
 
     G4double fEpsilonMin; 
     G4double fEpsilonMax;
       // Values for the small possible relative accuracy of a step
       // (corresponding to the greatest possible integration accuracy)
 };
 
 // Implementation of inline functions
 
 #include "G4FieldManager.icc"
 
 #endif

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