Systems Simulation with Digital Computers

A machine-independent examination of the associated programming problem i s conducted and illustrated by means of a n example. Finally, the nature and application of simulation languages are noted. By system, we have in mind the meaning accorded by Webster, " a set of objects united by some form of regular interaction or interdependence. " Change in a system is regarded as change in the properties of the objects or in the relationships between the objects. That is, when one considers a physical system or conceives of a hypothetical system, one perceives certain distinct objects such as machines, customers, messages, etc. Each object is seen to possess certain properties of interest that may be used to define it, machine availability, credit status, or length of a message. Most important, one perceives certain changes taking place as a result of events in the system. These changes, such as the loading of a machine, making a payment, or sending a message, describe relations among the objects and determine changes in the values of their properties. Associated with the design of a system, two objectives are always present. We wish to: 1. Be able to predict performance before the system is built. 2. Have assurance that the system design selected is optimal in terms of the design criteria adopted. Consequently, systems studies are frequently conducted with some representation of the system, called a model. By working with a properly constructed model, the systems engineer is able to make inferences about a proposed system from experiments conducted with the system model (Figure 1) and accomplish the