Locally associated graphical models
The notion of multivariate total positivity has proved to be useful in finance and psychology but may be too restrictive in other applications. In this paper we propose a concept of local association, where highly connected components in a graphical model are positively associated and study its properties. Our main motivation comes from gene expression data, where graphical models have become a popular exploratory tool. We focus the exposition on Gaussian distributions but our methods readily extend to non-paranormal distributions. Motivated by a convex optimization problem that arises in this context, we develop a GOLAZO approach that generalizes a number of optimization procedures that arise in the context of graphical models (e.g. the GLASSO) and propose a simple block-coordinate descent optimization procedure for solving the dual problem. Our results on existence of the optimum for such problems are of separate interest.
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