Simulation is a very broad term that is applied across many fields and industries. In its most general sense, simulation is the process of building or designing a model that mimics the behavior of a particular real-life system. These models can be either physical or logical. Examples of physical models include flight simulators, wind tunnels, and earthquake simulators. This document focuses on logical models, which can usually be represented by computer programs.

For some systems governed by logical and mathematical relationships, you can use traditional mathematical techniques such as queueing theory and differential equations to derive an analytical solution. For these systems, obtaining an exact answer is a benefit. However, you often need to make simplifying assumptions about the system being studied in order to obtain an analytical model; this simplification brings to the forefront the question of model validity. You can build a simple model of a complex system, but that does not necessarily mean that the model is valid.

Many real-world systems are composed of not only extremely complicated and intricate mathematical and logical relationships, but also a significant random component. For these systems, you simply might not be able to derive an analytical model. Instead, you can use a computer to build a model of the system and numerically generate data that you can use to foster a better understanding of the behavior of the real-world system. Part of the art of designing a computer simulation model is deciding which aspects of the real-life system are necessary to include in the model so that the data generated by the model can be used to make effective decisions.

One of the main advantages of computer simulation is the ability to model extremely complex systems that ordinarily would be impossible to model using traditional analytical techniques. On the other hand, the data generated by a computer simulation model is not exact and, to complicate matters even further, the output is random if any of the model’s inputs is random. This randomness makes it more difficult to analyze the output from computer simulations, and often advanced statistical methods are required to formulate valid conclusions about the behavior of the system.

The field of computer-based simulation is itself very broad and includes a number of different classes of modeling techniques. This document focuses primarily on discrete-event modeling methods in which the state of the model is dynamic and the state of the model changes only at countable, distinct points in time. For example, the operation of an emergency room at a hospital over a 24-hour period can be modeled using discrete-event simulation techniques. A state change in this example can be triggered by the arrival of a new patient or the departure of a nurse for a meal break. Each state change occurs at a distinct point in time, and the simulation model operates by scheduling these events and proceeds by advancing the simulation time to the next event or state change.

The popularity of simulation as a tool for design and analysis has grown over recent years, especially with the advancement of computing technology. Part of simulation’s popularity is also due to the numerous and diverse areas where it can be applied. Some areas where discrete-event simulation has been successfully used include manufacturing, telecommunications, transportation, military, and health care.