Efficient simulations by queue machines

Abstract

The following simulations by machines equipped with a one-way input tape and additional queue storage are shown: Every single-tape Turing machine (no separate input-tape) with time bound t(n) can be simulated by one queue in O(t(n)) time. Every pushdown automaton can be simulated by one queue in time O(n√n). Every deterministic machine with a one-turn pushdown store can be simulated deterministically by one queue in O(n√n) time. Every Turing machine with several multi-dimensional tapes accepting with time bound t(n) can be simulated by two queues in time O(t(n) log2 t(n)). Every deterministic Turing machine with several linear tapes accepting with time bound t(n) can be simulated deterministically by a queue and a pushdown store in O(t(n) log t(n)) time. The former results appear to be the first sub-quadratic simulations of other storage devices such as pushdowns or tapes by one queue. The simulations of pushdown machines almost match the corresponding lower bounds.KeywordsTuring MachineInput TapeDeterministic SimulationPushdown AutomatonDeterministic Turing MachineThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.