# Session 45: New insights into classical statistical methods

Session title: New insights into classical statistical methods
Organizer: Qing Mai (Florida State U)
Chair: Qing Mai (Florida State U)
Time: June 6th, 3:15pm – 4:45pm
Location: VEC 404/405

Speech 1: Rank-constrained inherent clustering paradigm for supervised and unsupervised learning
Speaker: Yiyuan She (Florida State U)
Abstract: Modern clustering applications are often faced with challenges from high dimensionality and/or nonconvex clusters. This paper gives a mathematical formulation of clustering with concurrent dimension reduction and proposes an optimization-based inherent clustering framework. Inherent clustering enjoys a kernel property to work on similarity matrices and can be extended to supervised learning. A simple-to-implement iterative algorithm is developed by use of linearization and block coordinate descent. Non-asymptotic analysis shows the tight error rate of inherent clustering in the supervised setting. Extensive simulations, as well as real-data experiments in network community detection and learning, demonstrate the excellent performance of the proposed approach.

Speech2:  Fast and Optimal Bayesian Inference via Variational Approximations
Speaker: Yun Yang (Florida State U)

Abstract: We propose a variational approximation to Bayesian posterior distributions, called $\alpha$-VB, with provable statistical guarantees for models with and without latent variables. The standard variational approximation is a special case of $\alpha$-VB with $\alpha=1$. When $\alpha \in(0,1)$, a novel class of variational inequalities are developed for linking the Bayes risk under the variationalapproximation to the objective function in the variational optimization problem, implying that maximizing the evidence lower bound in variational inference has the effect of minimizing the Bayes risk within the variational density family. Operating in a frequentist setup, the variational inequalities imply that point estimates constructed from the $\alpha$-VB procedure converge at an optimal rate to the true parameter in a wide range of problems. We illustrate our general theory with a number of examples, including the mean-field variational approximation to (low)-high-dimensional Bayesian linear regression with spike and slab priors, mixture of Gaussian models, latent Dirichlet allocation, and (mixture of) Gaussian variational approximation in regular parametric models.

Speech 3: An Iterative Penalized Least Squares Approach to Sparse Canonical Correlation Analysis
Speaker: Xin Zhang (Florida State U)
Abstract: It is increasingly interesting to model the relationship between two sets of measurements when both of them are high-dimensional. Canonical correlation analysis (CCA) is a classical tool that explores the dependency of two multivariate random variables and extracts canonical pairs of highly correlated linear combinations. Driven by applications in genomics, text mining and imaging research among others, many recent studies generalize CCA to high-dimensional settings. However, most of them either rely on strong assumptions on the covariance matrices, or does not produce nested solutions. We propose a new sparse CCA (SCCA) method that recasts high-dimensional CCA as an iterative penalized least squares problem. Thanks to the new penalized least squares formulation, our SCCA method directly penalizes and estimates the sparse CCA directions with efficient algorithms. Therefore, in contrast to some existing methods, the new SCCA does not impose any sparsity assumptions on the covariance matrices. The proposed SCCA is also very flexible in the sense that it can be easily combined with properly chosen penalty functions to perform structured variable selection or to incorporate prior information. Moreover, our proposal of SCCA produces nested solutions, which provides great convenient in practice. Theoretical results show that SCCA can consistently estimate the true canonical pairs with an overwhelming probability in ultra-high dimensions. Numerical results also demonstrate the competitive performance of SCCA.