Zusammenfassung
Recently, there has been a surge of interest in community detection
algorithms for complex networks. The proposed algorithms are based on a variety
of heuristics, some with a long history, for the identification of communities
or, alternatively, of good graph partitions. In most cases, the algorithms
proceed by maximizing a particular objective function, thereby finding the
`right' split into communities. Although a thorough comparative analysis of
these algorithms is still lacking, there has also been an effort to design
random graph models with known community structure against which the
performance of different algorithms can be benchmarked. However, such
benchmarks normally impose not only a known community structure but also a
clique-like random structure for the communities which may differ significantly
from those found in real networks. We show here that popular community
detection methods are affected by a restricted `field-of-view' limit, an
intrinsic upper scale that does not allow them to detect communities with large
effective diameters. Such long-range communities are widespread in real
networks, specifically in those that emerge from geometric constraints. In
consequence, the performance of algorithms on clique-like benchmarks, which are
inherently of low diameter, may not be indicative of equally good results in
real networks with sparser connectivity. We show that by adopting a dynamical
perspective towards community detection (Delvenne et al. (2010) PNAS:107:
12755-12760; Lambiotte et al. (2008) arXiv:0812.1770), in which the evolution
of a Markov process acts as a zooming lens over the structure of the graph at
all scales, one can detect robust communities without imposing an intrinsic
upper scale to the communities. We illustrate our ideas with constructive
examples and through the analysis of real-world networks from imaging, protein
structure and the power grid.
Nutzer