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arXiv 2106.10201cs.DCcs.DS
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一种求解精确多数的时空最优稳定种群协议

A time and space optimal stable population protocol solving exact majority

David Doty, Mahsa Eftekhari, Leszek Gąsieniec, Eric Severson, Grzegorz Stachowiak, Przemysław Uznański

摘要:

我们研究人口协议,分布式计算模型适合建模良好混合的化学反应网络和其他物理系统,代理人在成对的相互作用交换信息,但没有控制他们的时间表的互动伙伴。经过充分研究的“多数”问题是,在初始的$n$主体群体中,每个主体都有两个意见之一:$A$或$B$,确定是否有更多的$A$、更多的$B$或平局。*stable* 协议解决这个问题的概率为1,它最终进入一个配置,在该配置中,所有代理都同意$\mathsf{A}$、$\mathsf{B}$或$\mathsf{T}$的正确共识决定,共识不能从该决定改变。我们描述了一个协议,解决了这个问题,使用$O(\log n)$状态($\log \log n + O(1)$位的内存)和最佳预期时间$O(\log n)$。已知状态数$O(\log n)$对于“输出占优”和“单调”的多对数时间稳定协议类是最优的。这是我们的协议满足的两个自然约束,使其同时对该类具有时间和状态最优性。我们引入了一个关键技术,称为“固定分辨率时钟”,以实现部分同步。我们的协议是 *nonuniform*:转换函数的值$\left \lceil {\log n} \right \rceil$编码在它。我们表明,该协议可以修改为统一的,而增加的状态复杂度$Θ(\log n \log \log n)$。

英文摘要:

We study population protocols, a model of distributed computing appropriate for modeling well-mixed chemical reaction networks and other physical systems where agents exchange information in pairwise interactions, but have no control over their schedule of interaction partners. The well-studied *majority* problem is that of determining in an initial population of $n$ agents, each with one of two opinions $A$ or $B$, whether there are more $A$, more $B$, or a tie. A *stable* protocol solves this problem with probability 1 by eventually entering a configuration in which all agents agree on a correct consensus decision of $\mathsf{A}$, $\mathsf{B}$, or $\mathsf{T}$, from which the consensus cannot change. We describe a protocol that solves this problem using $O(\log n)$ states ($\log \log n + O(1)$ bits of memory) and optimal expected time $O(\log n)$. The number of states $O(\log n)$ is known to be optimal for the class of polylogarithmic time stable protocols that are "output dominant" and "monotone". These are two natural constraints satisfied by our protocol, making it simultaneously time- and state-optimal for that class. We introduce a key technique called a "fixed resolution clock" to achieve partial synchronization. Our protocol is *nonuniform*: the transition function has the value $\left \lceil {\log n} \right \rceil$ encoded in it. We show that the protocol can be modified to be uniform, while increasing the state complexity to $Θ(\log n \log \log n)$.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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