Editing General Geant4 Overview (section)

===Runs, Events, and Steps===

Geant4 simulations are broken into three levels runs, events, and steps. A run is a complete simulation, as in each time you run the program. Tasks executed at this level happen once per execution of the program. An event is the level below a run. When you use the run/beamOn command, your actually giving the program the number of events to execute after the command. An event is fairly flexible, but often it is a single particle being shot. The smallest level is a step. Each event is broken into a series of steps. Steps can be a certain amount of time passing, entering or exiting a volume, or a particle decaying. It is important to note that variables created in one level must be included in the others to be seen. This is done by including (#include "<example>.hh") the header file of the other class that holds the variable that needs to be used. Also, the variable in the other class must be public, or getters and setters must be used. Understanding at what level specific tasks should be handled is essential to designing a properly functioning program, so be sure to consider these concepts when deciding how to code your simulation.