Abstract
We introduce a method for the theoretical analysis of exponential random
graph models. The method is based on a large-deviations approximation to the
normalizing constant shown to be consistent using theory developed by
Chatterjee and Varadhan European J. Combin. 32 (2011) 1000-1017. The theory
explains a host of difficulties encountered by applied workers: many distinct
models have essentially the same MLE, rendering the problems ``practically''
ill-posed. We give the first rigorous proofs of ``degeneracy'' observed in
these models. Here, almost all graphs have essentially no edges or are
essentially complete. We supplement recent work of Bhamidi, Bresler and Sly
2008 IEEE 49th Annual IEEE Symposium on Foundations of Computer Science (FOCS)
(2008) 803-812 IEEE showing that for many models, the extra sufficient
statistics are useless: most realizations look like the results of a simple
Erd\Hos-Rényi model. We also find classes of models where the limiting
graphs differ from Erd\Hos-Rényi graphs. A limitation of our approach,
inherited from the limitation of graph limit theory, is that it works only for
dense graphs.
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