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A Generalised Twinning Property for Minimisation of Cost Register Automata*

机译:最小化成本登记自动机的广义孪生属性*

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Weighted automata (WA) extend finite-state automata by associating with transitions weights from a semiring S, defining functions from words to S. Recently, cost register automata (CRA) have been introduced as an alternative model to describe any function realised by a WA by means of a deterministic machine. Unambiguous WA over a monoid (M,⊗) can equivalently be described by cost register automata whose registers take their values in M, and are updated by operations of the form x :=y⊗c, with c ϵ M. This class is denoted by CRA⊗cM. We introduce a twinning property and a bounded variation property parametrised by an integer k, such that the corresponding notions introduced originally by Choffrut for finite-state transducers are obtained for k=1. Given an unambiguous weighted automaton W over an infinitary group (G,⊗) realizing some function f, we prove that the three following properties are equivalent: i) W satisfies the twinning property of order k, ii) f satisfies the k-bounded variation property, and iii) f can be described by a CRA⊗c(G) with at most k registers.In the spirit of tranducers, we actually prove this result in a more general setting by considering machines over the semiring of finite sets of elements from (G,⊗) : the three properties are still equivalent for such finite-valued weighted automata, that is the ones associating with words subsets of G of cardinality at most ℓ, for some natural ℓ. Moreover, we show that if the operation ⊗ of G is commutative and computable, then one can decide whether a WA satisfies the twinning property of order k. As a corollary, this allows to decide the register minimisation problem for the class CRA⊗c(G). Last, we prove that a similar result holds for finite-valued finite-state transducers, and that the register minimisation problem for the class CRA.c(B*) is PSPACE-complete.
机译:加权自动机(WA)通过与来自半环S的过渡权重相关联来扩展有限状态自动机,定义从单词到S的功能。最近,已经引入了成本寄存器自动机(CRA)作为替代模型来描述由WA实现的任何功能通过确定性机器。等价类集(M,⊗)上的明确WA可以等效地由成本寄存器自动机描述,其寄存器的值以M为单位,并通过x:=y⊗c形式的操作进行更新,其中c ϵM。通过CRA ⊗c M.我们引入参数为整数k的孪生性质和有界变化性质,以便在k = 1的情况下获得Choffrut最初为有限状态换能器引入的相应概念。给定一个实现函数f的不定式(G,⊗)上明确的加权自动机W,我们证明以下三个性质是等价的:i)W满足k阶孪生性质,ii)f满足k界变化属性,并且iii)f可以由CRA描述 ⊗c (G)最多具有k个寄存器。在换能器的精神上,我们实际上通过考虑机器对(G,⊗)有限元集的半环进行了证明,从而证明了这一结果是更通用的:这三个属性对于这样的有限值加权自动机,即对于某些自然ℓ,它最多与基数的G的单词子集相关联。此外,我们表明,如果G的运算is是可交换的并且是可计算的,则可以确定WA是否满足k级的孪生性质。因此,可以确定类CRA的寄存器最小化问题 ⊗c (G)。最后,我们证明了有限值有限状态换能器的相似结果,并且证明了CRA类的寄存器最小化问题。 c (B * )是PSPACE完整的。

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