Simulation

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Wooden mechanical horse simulator during WWI.
Wooden mechanical horse simulator during WWI.

A simulation is an imitation of some real thing, state of affairs, or process. The act of simulating something generally entails representing certain key characteristics or behaviors of a selected physical or abstract system.

Historically, the word had negative connotations:

…for Distinction Sake, a Deceiving by Words, is commonly called a Lye, and a Deceiving by Actions, Gestures, or Behavior, is called Simulation… Robert South (1643-1716)[1]

However, the connection between simulation and dissembling later faded out and is now only of linguistic interest.

Simulation is used in many contexts, including the modeling of natural systems or human systems in order to gain insight into their functioning. Other contexts include simulation of technology for performance optimization, safety engineering, testing, training and education. Simulation can be used to show the eventual real effects of alternative conditions and courses of action.

Key issues in simulation include acquisition of valid source information about the referent, selection of key characteristics and behaviours, the use of simplifying approximations and assumptions within the simulation, and fidelity and validity of the simulation outcomes.

Contents

[edit] Types of simulation

Historically, simulations used in different fields developed largely independently, but 20th century studies of Systems theory and Cybernetics combined with spreading use of computers across all those fields have led to some unification and a more systematic view of the concept.

[edit] Physical and interactive simulation

Physical simulation refers to simulation in which physical objects are substituted for the real thing. These physical objects are often chosen because they are smaller or cheaper than the actual object or system.

Interactive simulation is a special kind of physical simulation, often referred to as a human in the loop simulation, in which physical simulations include human operators, such as in a flight simulator.

[edit] Computer simulation

Main article: Computer simulation

A computer simulation is an attempt to model a real-life situation on a computer so that it can be studied to see how the system works. By changing variables, predictions may be made about the behaviour of the system.

An interesting application of computer simulation is to simulate computers using computers. The related software is called computer architecture simulators, which can be further divided into instruction set simulators or full system simulators.

Computer simulation has become a useful part of modeling many natural systems in physics, chemistry and biology, and human systems in economics and social science (the computational sociology) as well as in engineering to gain insight into the operation of those systems. A good example of the usefulness of using computers to simulate can be found in the field of network traffic simulation. In such simulations the model behaviour will change each simulation according to the set of initial parameters assumed for the environment. Computer simulations are often considered to be human out of the loop simulations.

Traditionally, the formal modeling of systems has been via a mathematical model, which attempts to find analytical solutions enabling the prediction of the behaviour of the system from a set of parameters and initial conditions. 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 would be prohibitive or impossible. In finance, for example, the risk-adjusted net present value is computed from well-defined but not always known (or fixed) inputs. By imitating the performance of the project under evaluation, simulation can provide a distribution of NPV over a range of discount rates and other inputs. Several software packages exist for running computer-based simulation modeling (e.g. Monte Carlo simulation and stochastic modeling) that makes the modeling almost effortless.

It is increasingly common to hear simulations of many kinds referred to as "synthetic environments". This label has been adopted to broaden the definition of "simulation" to encompass virtually any computer-based representation.

[edit] Simulation in computer science

In computer science, simulation has an even more specialized meaning: Alan Turing uses the term "simulation" to refer to what happens when a digital computer runs a state transition table (runs a program) that describes the state transitions, inputs and outputs of a subject discrete-state machine. The computer simulates the subject machine.

In computer architecture, a simulator is often used to execute a program that has to run on some inconvenient type of computer, or in a tightly controlled testing environment (see Computer architecture simulator). For example, simulators are usually used to debug a microprogram or sometimes commercial application programs. Since the operation of the computer is simulated, all of the information about the computer's operation is directly available to the programmer, and the speed and execution of the simulation can be varied at will.

Simulators may also be used to interpret fault trees, or test VLSI logic designs before they are constructed. Symbolic simulation is a form of simulation that is also an abstract interpretation of the concrete system under analysis.

In theoretical computer science the term simulation represents a relation between state transition systems. This is useful in the study of operational semantics.

[edit] Simulation in training

A soldier tests out a heavy-wheeled-vehicle driver simulator.
A soldier tests out a heavy-wheeled-vehicle driver simulator.

Simulation is often used in the training of civilian and military personnel. This usually occurs when it is prohibitively expensive or simply too dangerous to allow trainees to use the real equipment in the real world. In such situations they will spend time learning valuable lessons in a "safe" virtual environment. Often the convenience is to permit mistakes during training for a safety-critical system.

Training simulations typically come in one of three categories:

  • "live" simulation (where real people use simulated (or "dummy") equipment in the real world);
  • "virtual" simulation (where real people use simulated equipment in a simulated world (or "virtual environment")), or
  • "constructive" simulation (where simulated people use simulated equipment in a simulated environment). Constructive simulation is often referred to as "wargaming" since it bears some resemblance to table-top war games in which players command armies of soldiers and equipment which move around a board.

[edit] Simulation in education

Simulations in education are somewhat like training simulations. They focus on specific tasks. In the past, video has been used for teachers and education students to observe, problem solve and role play; however, a more recent use of simulations in education include animated narrative vignettes (ANV). ANVs are cartoon-like video narratives of hypothetical and reality-based stories involving classroom teaching and learning. ANVs have been used to assess knowledge, problem solving skills and dispositions of children, and pre-service and in-service teachers.

Another form of simulation has been finding favour in business education in recent years. Business simulations that incorporate a dynamic model enables experimentation with business strategies in a risk free environment and provide a useful extension to case study discussions.

[edit] Medical Simulators

Medical simulators are increasingly being developed and deployed to teach therapeutic and diagnostic procedures as well as medical concepts and decision making to personnel in the health professions. Simulators have been developed for training procedures ranging from the basics such as blood draw, to laparoscopic surgery and trauma care. They are also important to help on prototyping new devices for biomedical engineering problems. Currently, simulators are applied to research and development of tools for new therapies, treatments and early diagnosis in medicine.

Many medical simulators involve a computer connected to a plastic simulation of the relevant anatomy. Sophisticated simulators of this type employ a life size mannequin which responds to injected drugs and can be programmed to create simulations of life-threatening emergencies. In others simulations, visual components of the procedure are reproduced by computer graphics techniques, while touch-based components are reproduced by haptic feedback devices combined with physical simulation routines computed in response to the user's actions. Medical simulations of this sort will often use 3D CT or MRI scans of patient data to enhance realism. Some medical simulations are developed to be widely distributed (such as via the web) and can be interacted with using standard computer interfaces, such as the keyboard and mouse.

Another important medical application of a simulator -- although, perhaps, denoting a slightly different meaning of simulator -- is the use of a placebo drug, a formulation which simulates the active drug in trials of drug efficacy (see Placebo (origins of technical term)).

[edit] History of Medical Simulation

The first medical simulators were simple models of human patients.

Since antiquity, these representations in clay and stone were used to demonstrate clinical features of disease states and their effects on humans. Models have been found from many cultures and continents. These models have been used in some cultures (e.g., Chinese culture) as a "diagnostic" instrument, allowing women to consult male physicians while maintaining social laws of modesty. Models are used today to help students learn the anatomy of the musculoskeletal system and organ systems.

[edit] Active models

Active models which attempt to reproduce living anatomy or physiology are recent developments.

The famous “Harvey” mannikin was developed at the University of Miami and is able to recreate many of the physical findings of the cardiology examination, including palpation, auscultation, and electrocardiography.

[edit] Interactive models

More recently, interactive models have been developed which respond to actions taken by a student or physician. Until recently, these simulations were two dimensional computer programs which acted more like a textbook than a patient. Computer simulations have the advantage of allowing a student to make judgements, and also to make errors. The process of iterative learning through assessment, evaluation, decision making, and error correction creates a much stronger learning environment than passive instruction.

[edit] Computer simulators

Simulators have been proposed as an ideal tool for assessment of students for clinical skills.

Programmed patients and simulated clinical situations, including mock disaster drills, have been used extensively for education and evaluation. These “lifelike” simulations are expensive, and lack reproducibility. A fully functional "3Pi" simulator would be the most specific tool available for teaching and measurement of clinical skills.

Such a simulator meets the goals of an objective and standardized examination for clinical competence. This system is superior to examinations which use "standard patients" because it permits the quantitative measurement of competence, as well as reproducing the same objective findings.

[edit] The "classroom of the future"

The "classroom of the future" will probably contain several kinds of simulators, in addition to textual and visual learning tools. This will allow students to enter the clinical years better prepared, and with a higher skill level. The advanced student or postgraduate will have a more concise and comprehensive method of retraining -- or of incorporating new clinical procedures into their skill set -- and regulatory bodies and medical institutions will find it easier to assess the proficiency and competency of individuals.

The classroom of the future will also form the basis of a clinical skills unit for continuing education of medical personnel; and in the same way that the use of periodic flight training assists airline pilots, this technology will assist practitioners throughout their career.

The simulator will be more than a "living" textbook, it will become an integral a part of the practice of medicine. The simulator environment will also provide a standard platform for curriculum development in institutions of medical education.

[edit] City Simulators / Urban Simulation

A City Simulator can be a game but can also be a tool used by urban planners to understand how cities are likely to evolve in response to various policy decisions. UrbanSim (developed at the University of Washington), ILUTE (developed at the University of Toronto) and Distrimobs (developed at the University of Bologna) are examples of modern, large-scale urban simulators designed for use by urban planners. City simulators are generally agent-based simulations with explicit representations for land use and transportation.

[edit] Flight simulators

Main article: Flight simulator

A flight simulator is used to train pilots on the ground. It permits a pilot to crash his simulated "aircraft" without being hurt. Flight simulators are often used to train pilots to operate aircraft in extremely hazardous situations, such as landings with no engines, or complete electrical or hydraulic failures. The most advanced simulators have high-fidelity visual systems and hydraulic motion systems. The simulator is normally cheaper to operate than a real trainer aircraft.

[edit] Home-built Flight Simulators

Main article: Flight simulator Simulation Game

Some people who use simulator software, especially flight simulator software, build their own simulator at home. Some people in order to further the realism of their homemade simulator, buy used cards and racks that still run the exact same software they did before they were disassembled from the actual machine itself. Though this brings along the problem of matching hardware and software, and the fact that hundreds of cards plug into many different racks, still, many find that is it well worth it. Some are very serious in building their simulator by buying real aircraft parts like complete nose sectionals of written off aircraft at aircraft boneyards. This permits people who are unable to perform their hobby in real life to simulate it.

[edit] Marine simulators

Bearing resemblance to flight simulators, marine simulators train a ships' personnel. Simulators like these are mostly used to simulate large or complex vessels, such as cruiseships and dredging ships. They often consist of a replication of a ships' bridge, with operating desk(s), and a number of screens on which the virtual surroundings are projected.

[edit] Engineering (Technology) simulation or Process simulation

Simulation is an important feature in engineering systems or any system that involves many processes. For example in electrical engineering, delay lines may be used to simulate propagation delay and phase shift caused by an actual transmission line. Similarly, dummy loads may be used to simulate impedance without simulating propagation, and is used in situations where propagation is unwanted. A simulator may imitate only a few of the operations and functions of the unit it simulates. Contrast with: emulate. (Source: Federal Standard 1037C)

Most engineering simulations entail mathematical modeling and computer assisted investigation. There are many cases, however, where mathematical modeling is not reliable. Simulation of fluid dynamics problems often require both mathematical and physical simulations. In these cases the physical models require dynamic similitude. Physical and chemical simulations have also direct realistic uses, rather than research uses; in chemical engineering, for example, process simulations are used to give the process parameters immediately used for operating chemical plants, such as oil refineries.

For example, discrete event simulation is often used in industrial engineering, operations management and operational research to model many systems (commerce, health, defence, manufacturing, logistics, etc.) for example, the value-adding transformation processes in businesses, and optimize business performance. Imagine a business, where each person could do 30 tasks, where thousands of products or services involved dozens of tasks in a sequence, where customer demand varied seasonally and forecasting was inaccurate- this is the domain where such simulation helps with business decisions across all functions. Related topics include Theory of Constraints, bottlenecks, and management consulting.

[edit] Simulation and games

Main article: Simulation game

Strategy games - both traditional and modern - may be viewed as simulations of abstracted decision-making for the purpose of training military and political leaders (see History of Go for an example of such a tradition). In a narrower sense, many video games are also simulators, implemented inexpensively. These are sometimes called "sim games". Such games can simulate various aspects of reality, from economics to piloting vehicles, such as flight simulators (described above). Another type of simulation is a government simulation which can be used to help the player understand certain aspects of political science - specifically cause and effect.

[edit] Notes

  1. ^ South, 1697, p.525.
    South was speaking of the differences between a falsehood and an honestly mistaken statement; the difference being that in order for the statement to be a lie the truth must be known, and the opposite of the truth must have been knowingly uttered.
    And, from this, to the extent to which a lie involves deceptive words, a simulation involves deceptive actions, deceptive gestures, or deceptive behavior.
    Thus, it would seem, if a simulation is false, then the truth must be known (in order for something other than the truth to be presented in its stead); and, for the simulation to simulate.
    Because, otherwise, one would not know what to offer up in simulation.
    Bacon’s essay Of Simulation and Dissimulation expresses somewhat similar views; it is also significant that Samuel Johnson thought so highly of South's definition, that he used it in the entry for simulation in his Dictionary of the English Language.

[edit] See also

[edit] References

  • R. Frigg and S. Hartmann, Models in Science. Entry in the Stanford Encyclopedia of Philosophy.
  • S. Hartmann, The World as a Process: Simulations in the Natural and Social Sciences, in: R. Hegselmann et al. (eds.), Modelling and Simulation in the Social Sciences from the Philosophy of Science Point of View, Theory and Decision Library. Dordrecht: Kluwer 1996, 77-100.
  • P. Humphreys, Extending Ourselves: Computational Science, Empiricism, and Scientific Method. Oxford: Oxford University Press, 2004.
  • Roger D. Smith: Simulation Article, Encyclopedia of Computer Science, Nature Publishing Group, ISBN 0-333-77879-0.
  • Roger D. Smith: "Simulation: The Engine Behind the Virtual World", eMatter, December, 1999.
  • Aldrich, C. (2003). Learning by Doing : A Comprehensive Guide to Simulations, Computer Games, and Pedagogy in e-Learning and Other Educational Experiences. San Francisco: Pfeifer - John Wiley & Sons.
  • Aldrich, C. (2004). Simulations and the future of learning: an innovative (and perhaps revolutionary) approach to e-learning. San Francisco: Pfeifer - John Wiley & Sons.
  • Percival, F., Lodge, S., Saunders, D. (1993). The Simulation and Gaming Yearbook: Developing Transferable Skills in Education and Training. London: Kogan Page.
  • South, R., "A Sermon Delivered at Christ-Church, Oxon., Before the University, Octob. 14. 1688: Prov. XII.22 Lying Lips are abomination to the Lord", pp.519-657 in South, R., Twelve Sermons Preached Upon Several Occasions (Second Edition), Volume I, Printed by S.D. for Thomas Bennet, (London), 1697.
  • Of Simulation and Dissimulation An essay by Francis Bacon.

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