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Berlin 2008 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 3: Statistical physics of complex networks I

DY 3.8: Talk

Monday, February 25, 2008, 12:15–12:30, A 053

(Un)detectable cluster structure in sparse networks — •Jörg Reichardt1 and Michele Leone21Universität Würzburg, Institut f. Theoretische Physik — 2ISI Foundation, Torino, Italy

We study the problem of recovering a known cluster structure in a sparse network, also known as the planted partitioning problem, by means of statistical mechanics. We find a sharp transition from un-recoverable to recoverable structure as a function of the separation of the clusters. For multivariate data, such transitions have been observed frequently, but always as a function of the number of data points provided, i.e. given a large enough data set, two point clouds can always be recognized as different clusters, as long as their separation is non-zero. In contrast, for the sparse networks studied here, a cluster structure remains undetectable even in an infinitely large network if a critical separation is not exceeded. We give analytic formulas for this critical separation as a function of the degree distribution of the network and calculate the shape of the recoverability-transition. Our findings have implications for unsupervised learning and data-mining in relational data bases and provide bounds on the achievable performance of graph clustering algorithms.

Ref.: pre-print: http://arxiv.org/abs/0711.1452

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