User Actions

Geant4 has two user initialization classes and one user action class whose methods the user must override in order to implement a simulation. They require the user to define the detector, specify the physics to be used, and define how initial particles are to be generated. These classes are described in Mandatory User Actions and Initializations.

Additionally, users may define any of several optional user actions, to collect data during event generation from steps, tracks, or whole events, to accumulate data during runs, or to modify the state of new tracks as they are created. These user actions are described in Optional User Actions.

To support the accumulation of data in the actions mentioned above, users may define subclasses for some of the container objects used during event generation and tracking. These are described in User Information Classes.