On Time Flow Mechanisms for Discrete System Simulation

Previous concepts of time flow mechanisms are inadequate for categorizing or describing the algorithms for time flow which may prove most efficient for a particular systems application. The work of Kiviat [6] provides a more meaningful categorization. The patrolling repairman problem serves as an example of the ambiguity and inconsistency in the use of fixed time and next-event classification. Three algorithms for time flow in the patrolling model are offered. Theoretical development is provided for the two more sophisticated algorithms--the variable increment (VIA) and the minimum increment comparison (MICA). Comparison of execution times for the three algorithms shows the constant increment (CI) to be generally more efficient. The concept of a continuum of algorithms for representing the passage of time is advanced. Fixed time methods with \Delta t considered a "clock tick" define one end of the continuum, and next-event methods utilizing strictly the push down/pop up stack approach define the other. Between these two extremes lie other algorithms possessing characteristics of both but which may prove more advantageous for any specific application of discrete system simulation.