I. Introduction
An elevator group control system (EGCS) is a kind of complex nonlinear discrete control system that systematically manages three or more elevators in a building in order to efficiently transport passengers. An EGCS consists of hall call buttons, car call buttons, elevators, and a group controller in which there is group control dispatching algorithm, the most important part of an EGCS. If a passenger wants to go to another floor, he or she presses a direction (hall call) button and waits for an elevator to arrive; in this case, the group controller selects the most appropriate elevator in the group, depending on the current positions, moving directions, current passengers' number in every elevator. Then the passenger enters the elevator and presses a floor (car call) button in the elevator. The objective of an EGCS is to provide passengers with high-quality service.