arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2103.10062cond-mat.stat-mechcond-mat.dis-nnphysics.soc-ph
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从单向街道到随机混合图上的渗流

From one-way streets to percolation on random mixed graphs

Vincent Verbavatz, Marc Barthelemy

摘要:

在大多数研究中,街道网络被认为是无向图,而单向街道及其对最短路径的影响通常被忽略。在这里,我们首先研究了世界上约$140$城市的单行道的经验效应。它们的存在导致了一种迂回,这种迂回在很大的距离范围内持续存在,并以非普适指数为特征。单向交通对最短路径模式的影响是双重的:它们在某些地区缓解了当地交通,但在其他地方造成了瓶颈。这一实证研究自然导致考虑一个混合图模型的2D规则格与无向链接和稀释的可变部分$p$随机定向链接,模仿存在的街道网络中的单向。我们研究了强连通分量(SCC)与$p$的大小,并证明了存在一个阈值$p_c$,高于该阈值SCC的大小为零。我们数值计算表明,这种转变是非平凡的晶格度小于$4$,并提供了一些分析论证。我们计算数值的临界指数为这个过渡,并确认以前的结果表明,他们定义了一个新的普适性类不同的定向和标准渗流。最后,我们表明,现实世界中的图的过渡可以理解与规则格的随机扰动。单向对图形属性的影响已经是一些数学研究的主题,我们的研究结果表明,这个问题也有有趣的联系与渗流,在统计物理学的经典模型。

英文摘要:

In most studies, street networks are considered as undirected graphs while one-way streets and their effect on shortest paths are usually ignored. Here, we first study the empirical effect of one-way streets in about $140$ cities in the world. Their presence induces a detour that persists over a wide range of distances and characterized by a non-universal exponent. The effect of one-ways on the pattern of shortest paths is then twofold: they mitigate local traffic in certain areas but create bottlenecks elsewhere. This empirical study leads naturally to consider a mixed graph model of 2d regular lattices with both undirected links and a diluted variable fraction $p$ of randomly directed links which mimics the presence of one-ways in a street network. We study the size of the strongly connected component (SCC) versus $p$ and demonstrate the existence of a threshold $p_c$ above which the SCC size is zero. We show numerically that this transition is non-trivial for lattices with degree less than $4$ and provide some analytical argument. We compute numerically the critical exponents for this transition and confirm previous results showing that they define a new universality class different from both the directed and standard percolation. Finally, we show that the transition on real-world graphs can be understood with random perturbations of regular lattices. The impact of one-ways on the graph properties were already the subject of a few mathematical studies, and our results show that this problem has also interesting connections with percolation, a classical model in statistical physics.

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