G4FieldManager.hh

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//
// $Id: G4FieldManager.hh 104525 2017-06-02 07:22:58Z gcosmo $
//
//  
// class 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.

// History:
// - 09.06.15 John Apostolakis, Fix to push G4FieldManager* to equation
// - 05.11.03 John Apostolakis, Added Min/MaximumEpsilonStep
// - 20.06.03 John Apostolakis, Abstract & ability to ConfigureForTrack
// - 10.03.97 John Apostolakis, 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=0, 
        G4ChordFinder *pChordFinder=0, 
        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();

   G4bool   SetDetectorField(G4Field *detectorField, int failMode= 0);  // =1 is for Debugging ## Was =0 
        // Pushes the field to the equation.
        //   ( New behaviour June 2015 - to avoid the simplest user confusion. )   
        // 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;  // virtual ?
       // Accuracy for boundary intersection.

     inline G4double GetDeltaOneStep() const;      // virtual ?
       // Accuracy for one tracking/physics step.

     inline void     SetAccuraciesWithDeltaOneStep(G4double valDeltaOneStep); 
       // Sets both accuracies, maintaining a fixed ratio for accuracties 
       // 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;
     inline void      SetMinimumEpsilonStep( G4double newEpsMin );
     // Minimum for Relative accuracy of a Step 

     inline G4double  GetMaximumEpsilonStep() const;
     inline void      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

  private:

     G4FieldManager(const G4FieldManager&);
     G4FieldManager& operator=(const G4FieldManager&);
       // Private copy constructor and assignment operator.

     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 )
   
  private:
     // Dependent objects -- with state that depends on tracking
     G4Field*        fDetectorField;
     G4ChordFinder*  fChordFinder;

     G4bool          fAllocatedChordFinder; // Did we used "new" to
              // create fChordFinder ?
     // INVARIANTS of tracking  ---------------------------------------
     // 
     //  1. CONSTANTS 
     const G4double  fEpsilonMinDefault;   // Can be 1.0e-5 to 1.0e-10 ...
     const G4double  fEpsilonMaxDefault;   // Can be 1.0e-3 to 1.0e-8 ...

     //  2. CHARACTERISTIC of field
     G4bool          fFieldChangesEnergy;

     //  3. PARAMETERS 
     // 
     //     Values for the required accuracies
     G4double  fDelta_One_Step_Value;      //  for one tracking/physics step
     G4double  fDelta_Intersection_Val;    //  for boundary intersection

     G4double  fDefault_Delta_One_Step_Value;   // = 0.25 * mm;
     G4double  fDefault_Delta_Intersection_Val; // = 0.1 * mm;

     //     Values for the small possible relative accuracy of a step
     //     (corresponding to the greatest possible integration accuracy)
     G4double  fEpsilonMin; 
     G4double  fEpsilonMax;

};

// Our current design and implementation expect 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.


// Implementation of inline functions

#include "G4FieldManager.icc"

#endif   /*  G4FIELDMANAGER_HH */