Editing Understanding the Function Hierarchy (section)

===Steps===

A step is the lowest level of a Geant4 simulation. Just like with runs and events, steps can be manipulated greatly by a user. This occurs in the stepping action file. Steps are a small period of time, entering or exiting a volume, and any kind of particle decay. The simulation actually breaks events into steps without having to define anything, however the user must define what to do at each step. Often this is recording some piece of data, like the energy of the particle.

It is important to remember that there are multiple steps within a single event, so if values are added during each step to an Ntuple, it will be difficult to identify the beginning or end of each event. It may be beneficial to flag your data in some way so it can be separated later by a ROOT macro. For example, if you have a column called energy that gets recorded at each step, it may be helpful to add an entry of negative one at the beginning of each event. Then in your ROOT macro, a simple if statement can be used to check for this flag and save the next set of data as belonging to a different event.