Geant4 User's Guide for Application Developers - Geant4 - CERN

Toolkit Fundamentals3.3.5. Print the list of unitsYou can print the list of units with the static function: G4UnitDefinition::PrintUnitsTable();or with the interactive command: /units/list3.4. Run3.4.1. Basic concept of RunIn Geant4, Run is the largest unit of simulation. A run consists of a sequence of events. Within a run, the detectorgeometry, the set up of sensitive detectors, and the physics processes used in the simulation should be kept unchanged.A run is represented by a G4Run class object. A run starts with BeamOn() method of G4RunManager.3.4.1.1. Representation of a runG4Run represents a run. It has a run identification number, which should be set by the user, and the number ofevents simulated during the run. Please note that the run identification number is not used by the Geant4 kernel,and thus can be arbitrarily assigned at the user's convenience.G4Run has pointers to the tables G4VHitsCollection and G4VDigiCollection. These tables are associated in casesensitive detectors and digitizer modules are simulated, respectively. The usage of these tables will be mentionedin Section 4.4 and Section 4.5.3.4.1.2. Manage the run proceduresG4RunManager manages the procedures of a run. In the constructor of G4RunManager, all of the manager classesin Geant4 kernel, except for some static managers, are constructed. These managers are deleted in the destructorof G4RunManager. G4RunManager must be a singleton, and the pointer to this singleton object can be obtainedby the getRunManager() static method.As already mentioned in Section 2.1, all of the user initialization classes and user action classes defined by theuser should be assigned to G4RunManager before starting initialization of the Geant4 kernel. The assignmentsof these user classes are done by SetUserInitialization() and SetUserAction() methods. All userclasses defined by the Geant4 kernel will be summarized in Chapter 6.G4RunManager has several public methods, which are listed below.Initialize()All initializations required by the Geant4 kernel are triggered by this method. Initializations are:• construction of the detector geometry and set up of sensitive detectors and/or digitizer modules,• construction of particles and physics processes,• calculation of cross-section tables.This method is thus mandatory before proceeding to the first run. This method will be invoked automaticallyfor the second and later runs in case some of the initialized quantities need to be updated.BeamOn(G4int numberOfEvent)This method triggers the actual simulation of a run, that is, an event loop. It takes an integer argument whichrepresents the number of events to be simulated.GetRunManager()This static method returns the pointer to the G4RunManager singleton object.GetCurrentEvent()This method returns the pointer to the G4Event object which is currently being simulated. This method isavailable only when an event is being processed. At this moment, the application state of Geant4, which is43