Date | 2016-02-12 |
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Speaker | Won Hwa Kim |

Dept. | University of Wisconsin - Madison |

Room | 27-116 |

Time | 14:00-15:00 |

A Gaussian graphical model shows conditional independences between the random variables, which can be used to setup specific hypothesis based analyses downstream. But most data involve a large list of ‘latent’variables that remain unobserved, yet affect the ‘observed’ variables substantially. Accounting for such latent variables falls outside the scope of standard inverse covariance matrix estimation, and is tackled via highly specialized optimization methods. We offer a unique harmonic analysis view of this problem. By casting the estimation of the precision matrix in terms of a composition of low-frequency latent variables and high-frequency sparse terms, we show how the problem can be formulated using a new wavelet-type expansion in non-Euclidean spaces. Our formalization poses the estimation problem entirely in the frequency space and shows how it can be solved by a simple sub-gradient scheme (involving a single variable). We provide a compelling set of scientific results on ~500 scans from the recently released HCP data where our algorithm recovers highly interpretable and sparse conditional dependencies between brain connectivity pathways and well-known covariates.

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