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arXiv 1608.03036cs.CGcs.ET
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抽象瓦片装配模型中有向系统的通用模拟需要无向性

Universal Simulation of Directed Systems in the abstract Tile Assembly Model Requires Undirectedness

Jacob Hendricks, Matthew J. Patitz, Trent A. Rogers

摘要:

Winfree的抽象瓦片组装模型(aTAM)作为自组装系统的数学模型,是研究自组装系统行为和能力的重要平台。aTAM能够进行图灵通用计算,允许算法自组装,其中组件可以被设计为使得管理其行为的规则迫使它们在组合时固有地执行指定的算法。为了增加其完整性,aTAM还被示出为本质上是通用的,这意味着存在单个瓦片集合,使得对于任何任意输入aTAM系统,该瓦片集合可以被配置成种子结构,该种子结构然后将使用该瓦片集合来引起自组装以模拟输入系统,仅以比例因子为模来捕获其全动态。然而,通用的模拟器先前给出的利用非确定性的瓷砖类型放置在几个关键位置时,遵循不同的组装顺序,即使在模拟一个有向系统,这意味着一个只有一个唯一的终端组件。问题就变成了非决定论是否是根本需要的。在这里,我们的回答是肯定的:aTAM中的有向系统类本质上不是普适的,这意味着对于本身总是有向的有向系统没有通用的模拟器。这提供了洞察自我组装,这本身就是一个根本的不确定性过程中的非决定性的作用。为了实现这一结果,我们利用强大的结果的计算复杂性层次结构,包括最好和最坏情况下的复杂性的可判定语言的紧边界,设计系统的精确可控的空间资源可用于嵌入式计算。我们还开发了新的技术,用于设计包含子系统的系统,这些子系统具有不相交,互斥的计算能力。

英文摘要:

As a mathematical model of self-assembling systems, Winfree's abstract Tile Assembly Model (aTAM) is a remarkable platform for studying the behaviors and powers of self-assembling systems. Capable of Turing universal computation, the aTAM allows algorithmic self-assembly, in which the components can be designed so that the rules governing their behaviors force them to inherently execute prescribed algorithms as they combine. Adding to its completeness, the aTAM was shown to also be intrinsically universal, which means that there exists a single tile set such that for any arbitrary input aTAM system, that tile set can be configured into a seed structure which will then cause self-assembly using that tile set to simulate the input system, capturing its full dynamics modulo only a scale factor. However, the universal simulator previously given makes use of nondeterminism in terms of tile types placed in several key locations when different assembly sequences are followed, even when simulating a directed system, meaning one that has exactly one unique terminal assembly. The question then became whether or not that nondeterminism is fundamentally required. Here, we answer that in the affirmative: the class of directed systems in the aTAM is not intrinsically universal, meaning there is no universal simulator for directed systems which itself is always directed. This provides insight into the role of nondeterminism in self-assembly, which is itself a fundamentally nondeterministic process. To achieve this result we leverage powerful results of computational complexity hierarchies, including tight bounds on both best and worst-case complexities of decidable languages, to design systems with precisely controllable space resources available to embedded computations. We also develop novel techniques for designing systems containing subsystems with disjoint, mutually exclusive computational powers.

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