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For Application Developers
User Actions


6.2 Optional User Actions


There are five virtual classes whose methods the user may override in order to gain control of the simulation at various stages. Each method of each action class has an empty default implementation, allowing the user to inherit and implement desired classes and methods. Objects of user action classes must be registered with G4RunManager.

G4UserRunAction

This class has three virtual methods which are invoked by G4RunManager for each run:
GenerateRun()
This method is invoked at the beginning of BeamOn. Because the user can inherit the class G4Run and create his/her own concrete class to store some information about the run, the GenerateRun() method is the place to instantiate such an object. It is also the ideal place to set variables which affect the physics table (such as production thresholds) for a particular run, because GenerateRun() is invoked before the calculation of the physics table.
BeginOfRunAction()
This method is invoked before entering the event loop. A typical use of this method would be to initialize and/or book histograms for a particular run. This method is invoked after the calculation of the physics tables.
EndOfRunAction()
This method is invoked at the very end of the run processing. It is typically used for a simple analysis of the processed run.

     class G4UserRunAction
     {
       public:
         G4UserRunAction();
         virtual ~G4UserRunAction();

       public:
         virtual G4Run* GenerateRun();
         virtual void BeginOfRunAction(const G4Run*);
         virtual void EndOfRunAction(const G4Run*);
     };

 
Source listing 6.2.1
G4UserRunAction

G4UserEventAction

This class has two virtual methods which are invoked by G4EventManager for each event:
beginOfEventAction()
This method is invoked before converting the primary particles to G4Track objects. A typical use of this method would be to initialize and/or book histograms for a particular event.

endOfEventAction()
This method is invoked at the very end of event processing. It is typically used for a simple analysis of the processed event.

     class G4UserEventAction 
     {
       public:
           G4UserEventAction() {;}
           virtual ~G4UserEventAction() {;}
           virtual void BeginOfEventAction(const G4Event*);
           virtual void EndOfEventAction(const G4Event*);
       protected:
           G4EventManager* fpEventManager;
     };
 
Source listing 6.2.2
G4UserEventAction

G4UserStackingAction

This class has three virtual methods, ClassifyNewTrack, NewStage and PrepareNewEvent which the user may override in order to control the various track stacking mechanisms. ExampleN04 could be a good example to understand the usage of this class.
ClassifyNewTrack() is invoked by G4StackManager whenever a new G4Track object is "pushed" onto a stack by G4EventManager. ClassifyNewTrack() returns an enumerator, G4ClassificationOfNewTrack, whose value indicates to which stack, if any, the track will be sent. This value should be determined by the user. G4ClassificationOfNewTrack has four possible values:
fUrgent - track is placed in the urgent stack
fWaiting - track is placed in the waiting stack, and will not be simulated until the urgent stack is empty
fPostpone - track is postponed to the next event
fKill - the track is deleted immediately and not stored in any stack.
These assignments may be made based on the origin of the track which is obtained as follows:
G4int parent_ID = aTrack->get_parentID();
where
parent_ID = 0 indicates a primary particle
parent_ID > 0 indicates a secondary particle
parent_ID < 0 indicates postponed particle from previous event.

 

NewStage() is invoked when the urgent stack is empty and the waiting stack contains at least one G4Track object. Here the user may kill or re-assign to different stacks all the tracks in the waiting stack by calling the stackManager->ReClassify() method which, in turn, calls the ClassifyNewTrack() method. If no user action is taken, all tracks in the waiting stack are transferred to the urgent stack. The user may also decide to abort the current event even though some tracks may remain in the waiting stack by calling stackManager->clear(). This method is valid and safe only if it is called from the G4UserStackingAction class. A global method of event abortion is
G4UImanager * UImanager = G4UImanager::GetUIpointer();
UImanager->ApplyCommand("/event/abort");

 

PrepareNewEvent() is invoked at the beginning of each event. At this point no primary particles have been converted to tracks, so the urgent and waiting stacks are empty. However, there may be tracks in the postponed-to-next-event stack; for each of these the ClassifyNewTrack() method is called and the track is assigned to the appropriate stack.

     #include "G4ClassificationOfNewTrack.hh"

     class G4UserStackingAction 
     {
       public:
           G4UserStackingAction();
           virtual ~G4UserStackingAction();
       protected:
           G4StackManager * stackManager;

       public:
     //---------------------------------------------------------------
     // virtual methods to be implemented by user
     //---------------------------------------------------------------
     //
           virtual G4ClassificationOfNewTrack 
             ClassifyNewTrack(const G4Track*);
     //
     //---------------------------------------------------------------
     //
           virtual void NewStage();
     //
     //---------------------------------------------------------------
     //
           virtual void PrepareNewEvent();
     //
     //---------------------------------------------------------------

     };
 
Source listing 6.2.3
G4UserStackingAction

G4UserTrackingAction

     //---------------------------------------------------------------
     //
     // G4UserTrackingAction.hh
     //
     // Description:
     //   This class represents actions taken place by the user at each
     //   end of stepping. 
     //
     //---------------------------------------------------------------

     ///////////////////////////
     class G4UserTrackingAction 
     ///////////////////////////
     {
     
     //--------
        public:
     //--------
     
     // Constructor & Destructor
        G4UserTrackingAction(){};
        virtual ~G4UserTrackingAction(){}
     
     // Member functions
        virtual void PreUserTrackingAction(const G4Track*){}
        virtual void PostUserTrackingAction(const G4Track*){}
     
     //----------- 
        protected:
     //----------- 
     
     // Member data
        G4TrackingManager* fpTrackingManager;
     
     };
 
Source listing 6.2.4
G4UserTrackingAction

G4UserSteppingAction

     //---------------------------------------------------------------
     //
     //  G4UserSteppingAction.hh
     //
     //  Description:
     //    This class represents actions taken place by the user at each
     //    end of stepping. 
     //
     //---------------------------------------------------------------
     
     ///////////////////////////
     class G4UserSteppingAction 
     ///////////////////////////
     {
     
     //--------
        public:
     //--------
     
     // Constructor and destructor
        G4UserSteppingAction(){}
        virtual ~G4UserSteppingAction(){}
     
     // Member functions
        virtual void UserSteppingAction(const G4Step*){}
     
     //----------- 
        protected:
     //----------- 
     
     // Member data
        G4SteppingManager* fpSteppingManager;
     
     };
 
Source listing 6.2.5
G4UserSteppingAction




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