Fig 3. Overview of MCell4 Scheduler.

The Scheduler executes time step iterations which consist of discrete events executed in this order: 1) A ReleaseEvent creates new molecules, 2) A DiffuseReactEvent implements diffusion of molecules, checks collisions, and executes reactions, 3) A MolRxnCountEvent counts numbers of molecules or how many times a reaction occurs, and 4) A VizOutputEvent stores molecule locations for visualization in CellBlender. Only the DiffuseReactEvent must be executed at each time step to move the time forward. The other events listed here are optional.