Discrete-event simulation: Difference between revisions

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A '''discrete-event simulation''' ('''DES''') models the operation of a [[system]] as a [[discrete time|discrete]] [[sequence of events|series of events]] in time. Each event occurs at a particular instant in time and marks a change of [[State (computer science)|state]] in the system.<ref>{{cite book|title=''Simulation – The practice of model development and use''|author=Stewart Robinson|publisher=Wiley|year=2004}}</ref> Between consecutive events, no change in the system is assumed to occur; thus the [[simulation]] time can directly jump into the occurrence time fromof onethe next event, towhich theis called 'next-event time progression'.

ThisIn contrastsaddition withto [[continuousnext-event simulation]]time inprogression, whichthere theis simulationalso continuouslyan tracksalternative theapproach, systemcalled dynamics over'fixed-increment time. Instead of being [[Event-driven programming|event-based]]progression', this is called an activity-based simulation;where time is broken up into small time slices and the system state is updated according to the set of events/activities happening in the time slice.<ref name="matloff">{{cite web|last=Matloff|first=Norm|title=Introduction to Discrete-Event Simulation and the SimPy Language|url=http://heather.cs.ucdavis.edu/~matloff/156/PLN/DESimIntro.pdf|accessdate=24 January 2013}}</ref> Because discrete-eventnot simulationsevery dotime notslice havehas to simulatebe everysimulated, a next-event time slice, theysimulation can typically run much faster than thea corresponding continuousfixed-increment time simulation.

Both forms of DES contrast with [[continuous simulation]] in which the system state is changed continuously over time on the basis of a set of differential equations defining the rates of change of state variables.

A more recent method is the three-phased approach to discrete event simulation (Pidd, 1998). In this approach, the first phase is to jump to the next chronological event. The second phase is to execute all events that unconditionally occur at that time (these are called B-events). The third phase is to execute all events that conditionally occur at that time (these are called C-events). The three phase approach is a refinement of the event-based approach in which simultaneous events are ordered so as to make the most efficient use of computer resources. The three-phase approach is used by a number of commercial simulation software packages, but from the user's point of view, the specifics of the underlying simulation method are generally hidden.