Definition
The Future Event List (FEL) is a core data structure used in Discrete Event Simulation (DES) to manage and schedule the chronological execution of events. It contains all events that are scheduled to occur in the “future” of the simulation time.
Why It Matters
The FEL is the ‘engine of time’ for digital simulations; without it, we could not accurately model complex systems like airports or manufacturing plants where thousands of events happen in a strictly causal sequence, making it the essential tool for optimizing high-stakes infrastructure.
Core Concepts
- Ordering: Events in the FEL are strictly sorted in non-decreasing order based on their timestamps.
- Execution Cycle:
- The event with the lowest timestamp (at the head of the list) is extracted.
- The simulation clock advances to that timestamp.
- The event routine is executed (changing system state).
- New events generated by that routine are inserted into the FEL in their correct sorted position.
- Data Structures: Typically implemented as a linked list, heap, or tree to ensure efficient insertion and extraction.
- Temporal Control: The FEL is not a state variable; it is a control mechanism that dictates how the simulation progresses through time.