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 behaviours of a selected physical or abstract system.
Historically, the word had negative connotations:
However, the connection between simulation and dissembling later faded out and is now only of linguistic interest. Robert South ( September 4, 1634 - July 8, 1716) was an English churchman A lie (also called prevarication) is a type of Deception in the form of an untruthful statement especially with the intention to deceive others often with the further
Simulation is used in many contexts, including the modeling of natural systems or human systems in order to gain insight into their functioning. Scientific modelling is the process of generating abstract, conceptual, Graphical and or mathematical models.  Other contexts include simulation of technology for performance optimization, safety engineering, testing, training and education. Technology is a broad concept that deals with a Species ' usage and knowledge of Tools and Crafts and how it affects a species' ability to control and adapt Safety engineering is an applied science strongly related to Systems engineering and the subset System Safety Engineering In scientific inquiry an experiment ( Latin: Ex- periri, "to try out" is a method of investigating particular types of research questions or The term training refers to the acquisition of knowledge skills and competencies as a result of the teaching of vocational or practical skills and knowledge Education encompasses both the Teaching and Learning of Knowledge, proper conduct, and technical competency 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.
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. The twentieth century of the Common Era began on Systems theory is an Interdisciplinary field of Science and the study of the nature of Complex systems in Nature, Society, and Cybernetics is the interdisciplinary study of the Structure of Complex systems especially Communication processes control mechanisms and Feedback
Physical simulation refers to simulation in which physical objects are substituted for the real thing (some circles use the term for computer simulations modelling selected laws of physics, but this article doesn't). Physics (Greek Physis - φύσις in everyday terms is the Science of Matter and its motion. 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 or a driving simulator. Driving Simulators are used for Entertainment as well as in Training of driver's education courses taught in educational institutions and private businesses
Human in the loop simulations can include a computer simulation as a so-called synthetic environment.
A computer simulation (or "sim") is an attempt to model a real-life or hypothetical 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. A prediction is a statement or claim that a particular Event will occur in the Future in more certain terms than a forecast. 
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. Scientific modelling is the process of generating abstract, conceptual, Graphical and or mathematical models. Physics (Greek Physis - φύσις in everyday terms is the Science of Matter and its motion. Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties Foundations of modern biology There are five unifying principles Economics is the social science that studies the production distribution, and consumption of goods and services. The social sciences comprise academic disciplines concerned with the study of the social life of human groups and individuals including Anthropology, Communication studies Computational sociology is a recently developed branch of Sociology that uses Computation to analyze social phenomena Engineering is the Discipline and Profession of applying technical and scientific Knowledge and A good example of the usefulness of using computers to simulate can be found in the field of network traffic simulation. Network traffic simulation is a process used in Telecommunications engineering to measure the efficiency of a communications network In such simulations, the model behaviour will change each simulation according to the set of initial parameters assumed for the environment. Scientific modelling is the process of generating abstract, conceptual, Graphical and or mathematical models.
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. Note The term model has a different meaning in Model theory, a branch of Mathematical logic. 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. A scenario (from Italian, that which is pinned to the scenery) is a synthetic description of an event or series of actions and events
Several software packages exist for running computer-based simulation modeling (e. g. Monte Carlo simulation and stochastic modeling) that makes the modeling almost effortless. Monte Carlo methods are a class of Computational Algorithms that rely on repeated Random sampling to compute their results Stochastic (from the Greek "Στόχος" for "aim" or "guess" means Random.
Modern usage of the term "computer simulation" may encompass virtually any computer-based representation.
In Computer science, simulation has some specialized meanings: Alan Turing (1912-1954) used 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. Computer science (or computing science) is the study and the Science of the theoretical foundations of Information and Computation and their Alan Mathison Turing, OBE, FRS (ˈt(jʊ(ərɪŋ (23 June 1912 &ndash 7 June 1954 was an English Mathematician The computer simulates the subject machine. Accordingly, in theoretical computer science the term simulation is a relation between state transition systems, useful in the study of operational semantics. Theoretical computer science is the collection of topics of Computer science that focuses on the more abstract logical and mathematical aspects of Computing, such In Theoretical computer science a simulation preorder is a relation between State transition systems associating systems which behave in the same way in In Theoretical computer science, a state transition system is an Abstract machine used in the study of Computation. In Computer science, operational semantics is a way to give meaning to Computer programs in a mathematically rigorous way
Less theoretically, an interesting application of computer simulation is to simulate computers using computers. In computer architecture, a type of simulator, typically called an emulator, 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). In Computer engineering, computer architecture is the conceptual design and fundamental operational structure of a Computer system An emulator duplicates (provides an emulation of the functions of one System using a different system so that the second system behaves like (and appears to In Computer science, a computer architecture Simulator, or an architectural simulator is a piece of software to model computer devices (or components to predict outputs and For example, simulators have been used to debug a microprogram or sometimes commercial application programs, before the program is downloaded to the target machine. Microprogramming (ie writing microcode) is a method that can be employed to implement Machine instructions in a CPU relatively easily often using less 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. Fault tree analysis (FTA is a failure analysis in which an undesired state of a system is analyzed using Boolean logic to combine a series of lower-level events Symbolic simulation uses variables to stand for unknown values. In computer science a Simulation is a computation of the execution of some appropriately modelled state-transition system
In the field of optimization, simulations of physical processes are often used in conjunction with evolutionary computation to optimize control strategies. In Mathematics, the term optimization, or mathematical programming, refers to the study of problems in which one seeks to minimize or maximize a real function In Computer science evolutionary computation is a subfield of Artificial intelligence (more particularly Computational intelligence) that involves
Simulation is often used in the training of civilian and military personnel. The term training refers to the acquisition of knowledge skills and competencies as a result of the teaching of vocational or practical skills and knowledge  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:
In standardized tests, "live" simulations are sometimes called "high-fidelity", producing "samples of likely performance", as opposed to "low-fidelity", "pencil-and-paper" simulations producing only "signs of possible performance", but the distinction between high, moderate and low fidelity remains relative, depending on the context of a particular comparison. A standardized test is a test administered and scored in a consistent manner
Simulations in education are somewhat like training simulations. They focus on specific tasks. The term 'microworld' is used to refer to educational simulations which model some abstract concept rather than simulating a realistic object or environment, or in some cases model a real world environment in a simplistic way so as to help a learner develop an understanding of the key concepts. Normally, a user can create some sort of constructions within the microworld which will behave in a way consistent with the concepts being modeled. Seymour Papert was one of the first to advocate the value of microworlds, and the Logo programming environment developed by Papert is one of the most famous microworlds. Seymour Papert (born February 29, 1928 in Pretoria South Africa) is an MIT Mathematician, computer scientist, and A logo ( Greek el λογότυπος = el-Latn logotypos is a graphical element ( Ideogram, Symbol, Emblem, Icon, Sign)
Management games (or business simulations) have been finding favour in business education in recent years.  Business simulations that incorporate a dynamic model enable experimentation with business strategies in a risk free environment and provide a useful extension to case study discussions.
A truck simulator provides an opportunity to reproduce the characteristics of real vehicles in a virtual environment. It replicates the external factors and conditions with which a vehicle interacts enabling a driver to feel as if they are sitting in the cab of their own vehicle. Scenarios and events are replicated with sufficient reality to ensure that drivers become fully immersed in the experience rather than simply viewing it as an educational programme.
The simulator provides a constructive experience for the novice driver and enables more complex exercises to be undertaken by the more mature driver. For novice drivers, truck simulators provide an opportunity to begin their career by applying best practice. For mature drivers, simulation provides the ability to enhance good driving or to detect poor practice and to suggest the necessary steps for remedial action. For companies, it provides an opportunity to educate staff in the driving skills that achieve reduced maintenance costs, improved productivity and, most importantly, to ensure the safety of their actions in all possible situations.
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. Laparoscopic surgery, also called Minimally invasive surgery (MIS, bandaid surgery, Keyhole surgery, or pinhole surgery 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 that responds to injected drugs and can be programmed to create simulations of life-threatening emergencies. In other 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. Computer graphics are Graphics created by Computers and more generally the Representation and Manipulation of Pictorial Data Medical simulations of this sort will often use 3D CT or MRI scans of patient data to enhance realism. Computed tomography (CT is a Medical imaging method employing Tomography. Some medical simulations are developed to be widely distributed (such as web-enabled simulations that can be viewed via standard web browsers) and can be interacted with using standard computer interfaces, such as the keyboard and mouse. In Computing, a keyboard is an Input device partially modelled after the typewriter keyboard which uses an arrangement of buttons or keys In Computing, a mouse (plural mice, mouse devices, or mouses)
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 that simulates the active drug in trials of drug efficacy (see Placebo (origins of technical term)). Placebo is a substance or procedure a patient accepts as medicine or therapy but which has no specific therapeutic activity Placebo is a substance or procedure a patient accepts as medicine or therapy but which has no specific therapeutic activity
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. Diagnosis is the identification by Process of elimination, of the nature of anything Models are used today to help students learn the anatomy of the musculoskeletal system and organ systems. Anatomy (from the Greek anatomia, from ana separate apart from and temnein, to cut up cut open is a branch of Biology that is the consideration The musculoskeletal system (also known as the locomotor system is an organ system that gives Animals the ability to physically move using the Muscles and
Active models that 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. The University of Miami (also known as Miami of Florida, UM, or just The U) is a private non-sectarian University founded in 1925 Cardiology (from Greek grc καρδίᾱ kardiā, "heart" and grc -λογία -logia) is the branch of Internal medicine Palpation used as part of a Physical examination in which an object is felt (usually with the hands of a Healthcare practitioner to determine its size shape firmness For the ancient monasterial worker see Auscultare Auscultation is the technical term for listening to the internal sounds of the body usually
More recently, interactive models have been developed that respond to actions taken by a student or physician. Until recently, these simulations were two dimensional computer programs that 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.
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 that use "standard patients" because it permits the quantitative measurement of competence, as well as reproducing the same objective findings. 
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. Competence is a standardized requirement for an individual to properly perform a specific job.
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.
Military simulations, also known informally as war games, are models in which theories of warfare can be tested and refined without the need for actual hostilities. Military simulations, also known informally as war games, are simulations in which theories of warfare can be tested and refined without the need for actual hostilities A military is an Organization authorized by its Nation to use force usually including use of Weapons in defending its Country (or by attacking They exist in many different forms, with varying degrees of realism. In recent times, their scope has widened to include not only military but also political and social factors.  Whilst many governments make use of simulation, both individually and collaboratively, little is known about the model's specifics outside professional circles.
In finance, computer simulations are often used for scenario planning. Mathematical finance is the branch of Applied mathematics concerned with the Financial markets. The field of finance refers to the concepts of Time, Money and Risk and how they are interrelated Risk-adjusted net present value, for example, is computed from well-defined but not always known (or fixed) inputs. Risk is a Concept that denotes the precise probability of specific eventualities Net present value ( NPV) or net present worth ( NPW) is defined as the total Present value (PV of a Time series of Cash flows By imitating the performance of the project under evaluation, simulation can provide a distribution of NPV over a range of discount rates and other variables. Discounts and allowancesIn Finance and Economics, discounting is the process of finding the present value of an amount of cash at some future date and along with
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. City-building games are a genre of computer game where players act as the overall planner and leader of a city looking down on it from above and being responsible 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. In Economics, an agent is an actor in a model that (generally solves an optimization problem
A flight simulator is used to train pilots on the ground. A flight simulator is a system that tries to copy or simulate, the experience of flying an aircraft 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.
Some people who use simulator software, especially flight simulator software, build their own simulator at home. A flight simulator is a system that tries to copy or simulate, the experience of flying an aircraft See also [[Game classification]] Video games are categorized into Genres based on their Gameplay interaction A simulation game is a Game that contains a mixture of skill, chance, and strategy to simulate an aspect of reality such as a Stock Some people — in order to further the realism of their homemade simulator — buy used cards and racks that run the same software used by the original machine. While this involves solving the problem of matching hardware and software — and the problem that hundreds of cards plug into many different racks — many still find that solving these problems is well worthwhile. Some are so serious about realistic simulation that they will buy real aircraft parts, like complete nose sections of written-off aircraft, at aircraft boneyards. Boneyards was the massive online server created for the Total Annihilation series of computer games by Cavedog Entertainment This permits people to simulate a hobby that they are unable to pursue in real life.
A robotics simulator is used to create embedded applications for a specific (or not) robot without being dependent on the 'real' robot. A robotics simulator is used to create embedded applications for a specific (or not Robot without depending "physically" on the actual robot thus saving In some cases, these applications can be transferred to the real robot (or rebuilt) without modifications. Robotics simulators allow reproducing situations that cannot be 'created' in the real world because of cost, time, or the 'uniqueness' of a resource. A simulator also allows fast robot prototyping. Many robot simulators feature physics engines to simulate a robot's dynamics. A physics engine is a Computer program that simulates Newtonian physics models using variables such as Mass, Velocity, Friction and A lot of simulators are based on open-source projects such as (Orca OpenSim) and commercial projects (Marilou Robotics Studio, Webots, Microsoft Robotics Studio, Visual Components)
Bearing resemblance to flight simulators, marine simulators train ships' personnel. Webots is a professional Robot simulator widely used in academic and education The most common marine simulators include:
Simulators like these are mostly used within maritime colleges, training institutions and navies. The Global Maritime Distress Safety System ( GMDSS) is an internationally agreed-upon set of Safety procedures types of equipment and communication protocols used 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.
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. Electrical engineering, sometimes referred to as electrical and electronic engineering, is a field of Engineering that deals with the study and application of Networking Propagation delay is defined as how long it takes for a certain amount of bytes to transfered over a medium The phase of an oscillation or wave is the fraction of a complete cycle corresponding to an offset in the displacement from a specified reference point at time t = 0 A transmission line is the material medium or structure that forms all or part of a path from one place to another for directing the transmission of energy Similarly, dummy loads may be used to simulate impedance without simulating propagation, and is used in situations where propagation is unwanted. A dummy load is a device used to simulate an electrical load usually for testing purposes Electrical impedance, or simply impedance, describes a measure of opposition to a sinusoidal Alternating current (AC A simulator may imitate only a few of the operations and functions of the unit it simulates. Contrast with: emulate. An emulator duplicates (provides an emulation of the functions of one System using a different system so that the second system behaves like (and appears to 
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. Similitude is a concept used in the testing of engineering models. 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. Chemical engineering is the branch of Engineering that deals with the application of Physical science (e
Simulation solutions are being increasingly integrated with CAx (CAD, CAM, CAE. . . . ) solutions and processes. The use of simulation throughout the product lifecycle, especially at the earlier concept and design stages, has the potential of providing substantial benefits. These benefits range from direct cost issues such as reduced prototyping and shorter time-to-market, to better performing products and higher margins. However, for some companies, simulation has not provided the expected benefits.
The research firm Aberdeen Group has found that nearly all best-in-class manufacturers use simulation early in the design process as compared to 3 of 4 laggards who do not.
The successful use of Simulation, early in the lifecycle, has been largely driven by increased integration of simulation tools with the entire CAD, CAM and PLM solution-set. Simulation solutions can now function across the extended enterprise in a multi-CAD environment, and include solutions for managing simulation data and processes and ensuring that simulation results are made part of the product lifecycle history. Teamcenter is an integrated suite of Product Lifecycle Management applications from Siemens PLM Software. The ability to use simulation across the entire lifecycle has been enhanced through improved user interfaces such as tailorable user interfaces and "wizards" which allow all appropriate PLM participants to take part in the simulation process.
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, or Kriegsspiel for a more recent example). A simulation game is a Game that contains a mixture of skill, chance, and strategy to simulate an aspect of reality such as a Stock A strategy game is a Game (eg computer, video or Board game) in which the players' decision-making skills have a high significance The game of Go originated in China. No one knows when the first game was played but by the 4th century BC it was considered a worthy pastime for a gentleman Kriegsspiel, from the German word for wargame was a system used for training officers in the Prussian army
Many other video games are simulators of some kind. Such games can simulate various aspects of reality, from business, to government, to construction, to piloting vehicles (see above). Business simulation games, or economic simulation games, An important facet of economic simulations is the Emergence of artificial systems gameplay and structures A government simulation or political simulation is a game that attempts to simulate the government and politics of all or part of a nation Construction and management simulation games (or CMS s are a type of Simulation game which task players to build expand or manage fictional communities or projects Vehicle simulation games are a genre of Video games which attempt to provide the player with a realistic interpretation of operating various kinds of vehicles