An electronic machine, control device, etc. It is the hypothetical source of/evidence for its existence is provided by: Sanskrit manas- "mind, spirit," matih "thought," munih "sage, seer " Avestan manah- "mind, spirit " Greek memona "I yearn," mania "madness," mantis "one who divines, prophet, seer " Latin mens "mind, understanding, reason," memini "I remember," mentio "remembrance " Lithuanian mintis "thought, idea," Old Church Slavonic mineti "to believe, think," Russian pamjat "memory " Gothic gamunds, Old English gemynd "memory, remembrance conscious mind, intellect. An apparatus that automatically performs certain actions by responding to preset controls or encoded instructions. It forms all or part of: admonish Ahura Mazda ament amentia amnesia amnesty anamnesis anamnestic automatic automaton balletomane comment compos mentis dement demonstrate Eumenides idiomatic maenad -mancy mandarin mania maniac manic mantic mantis mantra memento mens rea mental mention mentor mind Minerva minnesinger mnemonic Mnemosyne money monition monitor monster monument mosaic Muse museum music muster premonition reminiscence reminiscent summon. A given input string may drive a nondeterministic pushdown automaton to one of several configuration sequences if one of them leads to an accepting configuration after reading the complete input string, the latter is said to belong to the language accepted by the automaton.Proto-Indo-European root meaning "to think," with derivatives referring to qualities and states of mind or thought. In general, if several actions are possible, then the automaton is called a general, or nondeterministic, PDA.
If, in every situation, at most one such transition action is possible, then the automaton is called a deterministic pushdown automaton (DPDA).
Put together: Given an input symbol, current state, and stack symbol, the automaton can follow a transition to another state, and optionally manipulate (push or pop) the stack. The automaton can alternatively ignore the stack, and leave it as it is. The manipulation can be to push a particular symbol to the top of the stack, or to pop off the top of the stack. A pushdown automaton can also manipulate the stack, as part of performing a transition. In each step, it chooses a transition by indexing a table by input symbol, current state, and the symbol at the top of the stack.
Automaton definition full#
Ī nested stack automaton allows full access, and also allows stacked values to be entire sub-stacks rather than just single finite symbols.Ī finite-state machine just looks at the input signal and the current state: it has no stack to work with. Stack automata can recognize a strictly larger set of languages than pushdown automata. 3 Altmetric Metrics Abstract Hybrid automata are an important formalism for modeling dynamical systems exhibiting mixed discretecontinuous behavior such as control systems and are amenable to formal verification. A stack automaton, by contrast, does allow access to and operations on deeper elements. 1 Formal definition A deterministic finite automaton M is a 5- tuple, (Q,, , q0, F), consisting of a finite set of states Q a finite set of input symbols called the alphabet a transition function : Q × Q an initial or start state a set of accept states Let w a1a2an be a string over the alphabet. The term "pushdown" refers to the fact that the stack can be regarded as being "pushed down" like a tray dispenser at a cafeteria, since the operations never work on elements other than the top element. American Heritage Anything that can move or act of itself. They are more capable than finite-state machines but less capable than Turing machines (see below).ĭeterministic pushdown automata can recognize all deterministic context-free languages while nondeterministic ones can recognize all context-free languages, with the former often used in parser design. noun automatons A self-operating machine or mechanism, especially a robot. Pushdown automata are used in theories about what can be computed by machines.
In the theory of computation, a branch of theoretical computer science, a pushdown automaton ( PDA) isĪ type of automaton that employs a stack. (Clicking on each layer gets an article on that subject)
0 kommentar(er)
