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In computer science, a computation history is a sequence of steps taken by an abstract machine in the process of computing its result. Computation histories are frequently used in proofs about the capabilities of certain machines, and particularly about the undecidability of various formal languages. Formally, a computation history is a (normally finite) sequence of configurations of a formal automaton. Each configuration fully describes the status of the machine at a particular point. To be valid, certain conditions must hold: * the first configuration must be a valid initial configuration of the automaton and * each transition between adjacent configurations must be valid according to the transition rules of the automaton. In addition, to be complete, a computation history must be finite and * the final configuration must be a valid terminal configuration of the automaton. The definitions of "valid initial configuration", "valid transition", and "valid terminal configuration" vary for different kinds of formal machines. A deterministic automaton has exactly one computation history for a given initial configuration, though the history may be infinite and therefore incomplete. == Finite State Machines == For a finite state machine , a configuration is simply the current state of the machine, together with the remaining input. The first configuration must be the initial state of and the complete input. A transition from a configuration to a configuration is allowed if for some input symbol and if has a transition from to on input . The final configuration must have the empty string as its remaining input; whether has accepted or rejected the input depends on whether the final state is an accepting state. 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Computation history」の詳細全文を読む スポンサード リンク
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