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A computer simulation, a '''computer model''' or a '''computational model''' is a Computer Program that attempts to Simulate an abstract Model of a particular system. Computer simulations have become a useful part of Mathematical Model ling of many natural systems in Physics ( Computational Physics ), Chemistry and Biology , human systems in Economics , Psychology , and Social Science and in the process of Engineering new Technology , to gain insight into the operation of those systems. Traditionally, the formal modeling of systems has been via a Mathematical Model , which attempts to find Analytical Solutions to problems which enables the prediction of the behaviour of the system from a set of parameters and initial conditions. Computer simulations build on, and are a useful adjunct to purely mathematical models in Science , Technology and Entertainment . HISTORY Computer simulation was developed hand-in-hand with the rapid growth of the computer, following its first large-scale deployment during the Manhattan Project in World War II to model the process of Nuclear Detonation . It was a simulation of 12 Hard Spheres using a Monte Carlo Algorithm . Computer simulation is often used as an adjunct to, or substitution for, modeling systems for which simple Closed Form Analytic Solutions are not possible. There are many different types of computer simulation; the common feature they all share is the attempt to generate a sample of representative scenarios for a model in which a complete enumeration of all possible states of the model would be prohibitive or impossible. Computer models were initially used as a supplement for other arguments, but their use later became rather widespread. DATA PREPARATION The data input/output for the simulation can be either through formatted Textfile s or a Pre- And Postprocessor . TYPES OF COMPUTER SIMULATION Computer models can be classified according to several criteria including:
For example:
COMPUTER SIMULATION IN SCIENCE Generic examples of types of computer simulations in science, which are derived from an underlying mathematical description:
Specific examples of computer simulations follow:
Notable, and sometimes controversial, computer simulations used in science include: Donella Meadows ' World3 used in the '' Limits To Growth '', James Lovelock 's Daisyworld and Thomas Ray's Tierra . Simulation environments for physics and engineering Graphical environments to design simulations have been developed. Special care was taken to handle events (situations in which the simulation equations are not valid and have to be changed). The open project Open Source Physics was started to develop reusable libraries for simulations in Java, together with Easy Java Simulations , a complete graphical environment that generates code based on these libraries. PITFALLS IN COMPUTER SIMULATION Although sometimes ignored in computer simulations, it is very important to perform Sensitivity Analysis to ensure that the accuracy of the results are properly understood. For example, the probabilistic risk analysis of factors determining the success of an oilfield exploration program involves combining samples from a variety of statistical distributions using the Monte Carlo Method . If, for instance, one of the key parameters (i.e. the net ratio of oil-bearing strata) is known to only one significant figure, then the result of the simulation might not be more precise than one significant figure, although it might (misleadingly) be presented as having four significant figures. COMPUTER SIMULATION IN PRACTICAL CONTEXTS Computer simulations are used in a wide variety of practical contexts, such as:
The reliability and the trust people put in computer simulations depends on the Validity of the simulation Model , therefore Verification and Validation are of crucial importance in the development of computer simulations. Another important aspect of computer simulations is that of reproducibility of the results, meaning that a simulation model should not provide a different answer for each execution. Although this might seem obvious, this is a special point of attention in stochastic simulations, where random numbers should actually be semi-random numbers. An exception to reproducibility are human in the loop simulations such as flight simulations and Computer Games . Here a human is part of the simulation and thus influences the outcome in a way that is hard if not impossible to reproduce exactly. Computer Graphics can be used to display the results of a computer simulation. Animations can be used to experience a simulation in real-time e.g. in training simulations. In some cases animations may also be useful in faster than real-time or even slower than real-time modes. For example, faster than real-time animations can be useful in visualizing the buildup of queues in the simulation of humans evacuating a building. Furthermore, simulation results are often aggregated into static images using various ways of Scientific Visualization . In debugging, simulating a program execution under test (rather than executing natively) can detect far more errors than the hardware itself can detect and, at the same time, log useful debugging information such as instruction trace, memory alterations and instruction counts. This technique can also detect Buffer Overflow and similar "hard to detect" errors as well as produce performance information and Tuning data. SEE ALSO
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