en>Gameboy97q: Typo fix

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	~~Luke~~ is ~~usually~~ a ~~celebrity~~ in the ~~producing~~ and the ~~job expansion initially second~~ to ~~his third studio album~~, ~~And~~ , ~~may~~ be the ~~proof~~. ~~He broken~~ on the ~~scene~~ in ~~2008 along with his special blend~~ of ~~downward~~-~~residence availability~~, ~~video legend fantastic appears~~ and ~~lines~~, is ~~defined t inside~~ a ~~key way~~. The ~~newest album Top around~~ the ~~region graph or chart~~ and ~~#2 around~~ the ~~put maps~~, ~~earning it~~ the ~~next greatest first appearance during~~ that ~~time~~ of ~~1999~~ for ~~any region performer~~. <br><br>The ~~son~~ of ~~your~~ , ~~knows determination~~ and ~~dedication are key elements~~ in terms of a ~~successful occupation~~- . ~~His initially record~~, ~~Keep Me~~, ~~made~~ the ~~Top strikes “All My Pals Say”~~ and ~~“Country Person~~,~~” when his work~~, ~~Doin’ Issue~~, ~~discovered~~ the ~~singer~~-~~about~~ [http://~~minioasis~~.~~com justin moore tour] three straight No~~. [http://~~www~~.~~banburycrossonline~~.~~com kid cudi tickets] 3 single men~~ and ~~women~~: ~~More Calling Is usually a Great Point~~.”<br><br>~~In the tumble~~ of ~~2011~~, ~~Concert tour: Luke Bryan And which had an outstanding set~~ of , ~~such as~~ [http://~~lukebryantickets~~.~~lazintechnologies~~.~~com luke bryan tickets go~~ on ~~sale~~] ~~Metropolitan~~. ~~“It’s much like you’re acquiring a acceptance to visit to a higher level, claims individuals designers that had been an element~~ of the ~~Concert toursover in a larger measure of musicians~~.~~” It packaged among the most successful tours in their twenty~~-~~season record~~.~~<br><br>Here is my homepage -~~ [http://www.~~hotelsedinburgh~~.org ~~ticket resale~~]		{{lead too long\|date=August 2010}}
			'''Reversible computing''' is a model of [[computing]] where the [[computational process]] to some extent is reversible, i.e., [[DTIME\|time]]-[[invertible function\|invertible]]. In a [[computational model]] that uses [[transition function\|transitions]] from one state of the abstract machine to another, a necessary condition for reversibility is that the relation of the mapping from states to their successors must be [[injective function\|one-to-one]]. Reversible computing is generally considered an [[Unconventional computing\|unconventional]] form of computing.

			There are two major, closely related, types of reversibility that are of particular interest for this purpose: ''physical reversibility'' and ''logical reversibility''.<ref>http://www.cise.ufl.edu/research/revcomp/</ref>

			A process is said to be ''physically reversible'' if it results in no increase in physical [[entropy]]; it is ''[[isentropic]]''. These circuits are also referred to as '''charge recovery logic''' or '''[[adiabatic]] computing'''. Although ''in practice'' no nonstationary physical process can be ''exactly'' physically reversible or isentropic, there is no known limit to the closeness with which we can approach perfect reversibility, in systems that are sufficiently well-isolated from interactions with unknown external environments, when the laws of physics describing the system's evolution are precisely known.

			Probably the largest motivation for the study of technologies aimed at actually implementing reversible computing is that they offer what is predicted to be the only potential way to improve the [[Energy conversion efficiency\|energy efficiency]] of computers beyond the fundamental [[von Neumann-Landauer limit]]<ref name="neumann">J. von Neumann, ''Theory of Self-Reproducing Automata'', Univ. of Illinois Press, 1966.</ref> of ''kT'' ln(2) energy dissipated per irreversible [[bit operation]].

			As was first argued by [[Rolf Landauer]] of [[IBM]],<ref>R. Landauer, "Irreversibility and heat generation in the computing process," IBM Journal of Research and Development, vol. 5, pp. 183-191, 1961.</ref> in order for a computational process to be physically reversible, it must also be ''logically reversible''. [[Landauer's principle]] is the loosely formulated notion that the erasure of ''n'' bits of information must always incur a cost of ''nk'' ln(2) in thermodynamic [[entropy]]. A discrete, deterministic computational process is said to be logically reversible if the transition function that maps old computational states to new ones is a [[one-to-one function]]; i.e. the output logical states uniquely defines the input logical states of the computational operation.

			For computational processes that are nondeterministic (in the sense of being probabilistic or random), the relation between old and new states is not a [[single-valued function]], and the requirement needed to obtain physical reversibility becomes a slightly weaker condition, namely that the size of a given ensemble of possible initial computational states does not decrease, on average, as the computation proceeds forwards.

			==The reversibility of physics and reversible computing==
			Landauer's principle (and indeed, the [[second law of thermodynamics]] itself) can also be understood to be a direct [[logical consequence]] of the underlying reversibility of [[physics]], as is reflected in the [[Hamiltonian mechanics\|general Hamiltonian formulation of mechanics]], and in the [[time evolution\|unitary time-evolution operator]] of [[quantum mechanics]] more specifically.

			In the context of reversible physics, the phenomenon of entropy increase (and the observed [[arrow of time]]) can be understood to be consequences of the fact that our evolved predictive capabilities are rather limited, and cannot keep perfect track of the exact reversible evolution of complex physical systems, especially since these systems are never perfectly isolated from an unknown external environment, and even the laws of physics themselves are still not known with complete precision. Thus, we (and physical observers generally) always accumulate ''some'' uncertainty about the state of physical systems, even if the system's true underlying dynamics is a perfectly reversible one that is subject to ''no'' entropy increase if viewed from a hypothetical omniscient perspective in which the dynamical laws are precisely known.

			The implementation of reversible computing thus amounts to learning how to characterize and control the physical dynamics of mechanisms to carry out desired computational operations so precisely that we can accumulate a negligible total amount of uncertainty regarding the complete physical state of the mechanism, per each logic operation that is performed. In other words, we would need to precisely track the state of the active energy that is involved in carrying out computational operations within the machine, and design the machine in such a way that the majority of this energy is recovered in an organized form that can be reused for subsequent operations, rather than being permitted to dissipate into the form of heat.

			Although achieving this goal presents a significant challenge for the design, manufacturing, and characterization of ultra-precise new physical mechanisms for [[computing]], there is at present no fundamental reason to think that this goal cannot eventually be accomplished, allowing us to someday build computers that generate much less than 1 bit's worth of physical entropy (and dissipate much less than ''kT'' ln 2 energy to heat) for each useful logical operation that they carry out internally.

			The motivation behind much of the research that has been done in reversible computing was the first seminal paper on the topic,<ref>C. H. Bennett, "Logical reversibility of computation," IBM Journal of Research and Development, vol. 17, no. 6, pp. 525-532, 1973.</ref><ref>C. H. Bennett, "The Thermodynamics of Computation -- A Review," International Journal of Theoretical Physics, vol. 21, no. 12, pp. 905-940, 1982.</ref> which was published by [[Charles H. Bennett (computer scientist)\|Charles H. Bennett]] of IBM research in 1973. Today, the field has a substantial body of academic literature behind it. A wide variety of reversible device concepts, [[logic gate]]s, [[electronic circuit]]s, [[processor architecture]]s, [[programming language]]s, and application [[algorithm]]s have been designed and analyzed by [[physicist]]s, [[electrical engineer]]s, and [[computer scientist]]s.

			This field of research awaits the detailed development of a high-quality, cost-effective, nearly reversible logic device technology, one that includes highly energy-efficient [[clocking]] and [[synchronization]] mechanisms. This sort of solid engineering progress will be needed before the large body of theoretical research on reversible computing can find practical application in enabling real computer technology to circumvent the various near-term barriers to its energy efficiency, including the von Neumann-Landauer bound. This may only be circumvented by the use of logically reversible computing, due to the [[Second Law of Thermodynamics]].

			==Reversible circuits==
			To implement reversible computation, estimate its cost, and to judge its limits, it is formalized it in terms of gate-level circuits. For example, the [[inverter (logic gate)]] (NOT) gate is reversible because it can be ''undone''. The [[exclusive or]] (XOR) gate is irreversible because its inputs cannot be unambiguously reconstructed from an output value. However, a reversible version of the XOR gate—the [[controlled NOT gate]] (CNOT)—can be defined by preserving one of the inputs. The three-input variant of the CNOT gate is called the [[Toffoli gate]]. It preserves two of its inputs ''a,b'' and replaces the third ''c'' by <math>c\oplus (a\cdot b)</math>. With <math>c=0</math>, this gives the AND function, and with <math>a\cdot b=1</math> this gives the NOT function. Thus, the Toffoli gate is universal and can implement any reversible [[Boolean function]] (given enough zero-initialized ancillary bits). More generally, reversible gates have the same number of inputs and outputs. A reversible circuit connects reversible gates without fanouts and loops. Therefore, such circuits contain equal numbers of input and output wires, each going through an entire circuit.

			Reversible logic circuits have been first motivated in the 1960s by theoretical considerations of zero-energy computation as well as practical improvement of [[bit manipulation\|bit-manipulation]] transforms in cryptography and computer graphics. Since the 1980s, reversible circuits have attracted interest as components of [[quantum algorithm]]s, and more recently in photonic and nano-computing technologies where some switching devices offer no [[signal gain]].

			Surveys of reversible circuits, their construction and optimization as well as recent research challenges is available.<ref>Rolf Drechsler, Robert Wille. From Truth Tables to Programming Languages: Progress in the Design of Reversible Circuits. International Symposium on Multiple-Valued Logic, 2011. http://www.informatik.uni-bremen.de/agra/doc/konf/11_ismvl_reversible_circuit_design_tutorial.pdf</ref><ref>Mehdi Saeedi, Igor L. Markov, Synthesis and Optimization of Reversible Circuits - A Survey, ACM Computing Surveys, 2012. http://arxiv.org/abs/1110.2574</ref><ref>Rolf Drechsler and Robert Wille. Reversible Circuits: Recent Accomplishments and Future Challenges for an Emerging Technology. International Symposium on VLSI Design and Test, 2012. http://www.informatik.uni-bremen.de/agra/doc/konf/2012_vdat_reversible_circuits_accompl_chall.pdf</ref>

			==See also==
			*[[Reversible dynamics]]
			*[[Maximum entropy thermodynamics]], on the uncertainty interpretation of the second law of thermodynamics
			*[[Reversible process]]
			*[[Toffoli gate]]
			*[[Fredkin gate]]
			*[[Quantum computing]]
			*[[Billiard-ball computer]]
			*[[Three-input universal logic gate]]
			*[[Undo]]
			*[[Reversible cellular automaton]]
			* [[Adiabatic circuit]]

			==References==
			<references/>
			Review of later theoretical work: P.M.B. Vitanyi, Time, space, and energy in reversible computing, Proceedings of the 2nd ACM conference on Computing frontiers, 2005, 435–444.

			==External links==
			*[http://strangepaths.com/reversible-computation/2008/01/20/en/ Introductory article on reversible computing]
			*[http://www.eng.fsu.edu/~mpf/CF05/RC05.htm First International Workshop on reversible computing]
			*[http://www.eng.fsu.edu/~mpf/pubs.htm Recent publications of Michael P. Frank]
			*[http://web.archive.org/web/20080626033214rn_1/revcomp.jot.com/WikiHome Internet Archive backup] of the "Reversible computing community Wiki" that was administered by Dr. Frank
			*[http://www.reversible-computation.org/ Recent Workshops on Reversible Computation]
			*[http://www.revkit.org/ Open-source toolkit for reversible circuit design]

			{{DEFAULTSORT:Reversible Computing}}
			[[Category:Digital electronics]]
			[[Category:Models of computation]]

en>ZéroBot: r2.7.1) (Robot: Adding ja:直線探索

2012-03-27T10:17:15Z

r2.7.1) (Robot: Adding ja:直線探索

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