Computation
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Computation is any type of calculation^{[1]}^{[2]} that includes both arithmetical and nonarithmetical steps and follows a welldefined model, for example an algorithm.
The study of computation is paramount to the discipline of computer science.
Contents
Physical phenomenon
A computation can be seen as a purely physical phenomenon occurring inside a closed physical system called a computer. Examples of such physical systems include digital computers, mechanical computers, quantum computers, DNA computers, molecular computers, microfluidicsbased computers, analog computers, or wetware computers. This point of view has been adopted by the physics of computation, a branch of theoretical physics, as well as the field of natural computing.
An even more radical point of view is the postulate of digital physics that argues that the evolution of the universe is itself a computation  pancomputationalism.
Accounts of computation
The mapping account
The classic account of computation is found throughout the works of Hilary Putnam and others. Peter GodfreySmith has dubbed this the “simple mapping account.”^{[3]} Gualtiero Piccinini's summary of this account states that a physical system can be said to perform a specific computation when there is a mapping between the state of that system to the computation such that the “microphysical states [of the system] mirror the state transitions between the computational states.”^{[4]}
The semantic account
Philosophers such as Jerry Fodor^{[5]} have suggested various accounts of computation with the restriction that semantic content be a necessary condition for computation (that is, what differentiates an arbitrary physical system from a computing system is that the operands of the computation represent something). This notion attempts to prevent the logical abstraction of the mapping account of pancomputationalism, the idea that everything can be said to be computing everything.
The mechanistic account
Gualtiero Piccinini proposes an account of computation based in mechanical philosophy. It states that physical computing systems are types of mechanisms that, by design, perform physical computation, or “the manipulation (by a functional mechanism) of a mediumindependent vehicle according to a rule.” Mediumindependence requires that the property is able to be instantiated by multiple realizers and multiple mechanisms and that the inputs and outputs of the mechanism also be multiply realizable. In short, mediumindependence allows for the use of physical variables with traits other than voltage (as in typical digital computers); this is imperative in considering other types of computation, such as that occurs in the brain or in a quantum computer. A rule, in this sense, provides a mapping among inputs, outputs, and internal states of the physical computing system. ^{[6]}
Mathematical models
In the theory of computation, a diversity of mathematical models of computers has been developed. Typical mathematical models of computers are the following:
 State models including Turing machine, pushdown automaton, finite state automaton, and PRAM
 Functional models including lambda calculus
 Logical models including logic programming
 Concurrent models including actor model and process calculi
Giunti (1997^{[7]}, ch. 1) calls the models studied by computation theory computational systems, and he argues that all of them are mathematical dynamical systems with discrete time and discrete state space. Giunti (2017^{[8]}, pp. 17980) maintains that a computational system is a complex object which consists of three parts. First, a mathematical dynamical systems DS with discrete time and discrete state space; second, a computational setup H = (F, B_{F}), which is made up of a theoretical part F, and a real part B_{F}; third, an interpretation I_{DS, H}, which links the dynamical system DS with the setup H.
See also
 Computationalism
 Physical information
 Real computation
 Reversible computation
 Hypercomputation
 Lateral computing
 Computational problem
 Multiple realizability
References
 ^ Computation from the Free MerriamWebster Dictionary
 ^ "Computation: Definition and Synonyms from Answers.com". Answers.com. Archived from the original on 22 February 2009. Retrieved 26 April 2017.
 ^ GodfreySmith, P. (2009), "Triviality Arguments against Functionalism", Philosophical Studies, 145 (2): 273–95, doi:10.1007/s1109800892313
 ^ Piccinini, Gualtiero (2015). Physical Computation: A Mechanistic Account. Oxford: Oxford University Press. p. 17. ISBN 9780199658855.
 ^ Fodor, J. A. (1981), "The MindBody Problem", Scientific American, 244 (January 1981)
 ^ Piccinini, Gualtiero (2015). Physical Computation: A Mechanistic Account. Oxford: Oxford University Press. p. 10. ISBN 9780199658855.
 ^ Giunti, Marco (1997). Computation, Dynamics, and Cognition. New York: Oxford University Press. ISBN 9780195090093.
 ^ Giunti, Marco (2017), "What is a Physical Realization of a Computational System?", Isonomia  Epistemologica, 9: 177–92, ISSN 20374348