February 03, 2016

"Fast Bayesian Factor Analysis via Automatic Rotations to Sparsity" (Next Week at the Statistics Seminar)

Attention conservation notice: Only of interest if (1) you care about factor analysis and Bayesian nonparametrics, and (2) will be in Pittsburgh on Monday.

Constant readers, knowing of my love-hate relationship with both factor analysis and with Bayesian methods will appreciate that the only way I could possibly be more ambivalent about our next seminar was if it also involved power-law distributions.

Veronika Ročková, "Fast Bayesian Factor Analysis via Automatic Rotations to Sparsity" [preprint, preprint supplement]
Abstract: Rotational post-hoc transformations have traditionally played a key role in enhancing the interpretability of factor analysis. Regularization methods also serve to achieve this goal by prioritizing sparse loading matrices. In this work, we bridge these two paradigms with a unifying Bayesian framework. Our approach deploys intermediate factor rotations throughout the learning process, greatly enhancing the effectiveness of sparsity inducing priors. These automatic rotations to sparsity are embedded within a PXL-EM algorithm, a Bayesian variant of parameter-expanded EM for posterior mode detection. By iterating between soft-thresholding of small factor loadings and transformations of the factor basis, we obtain (a) dramatic accelerations, (b) robustness against poor initializations and (c) better oriented sparse solutions. To avoid the pre-specification of the factor cardinality, we extend the loading matrix to have infinitely many columns with the Indian Buffet Process (IBP) prior. The factor dimensionality is learned from the posterior, which is shown to concentrate on sparse matrices. Our deployment of PXL-EM performs a dynamic posterior exploration, outputting a solution path indexed by a sequence of spike-and-slab priors. For accurate recovery of the factor loadings, we deploy the Spike-and-Slab LASSO prior, a two-component refinement of the Laplace prior (Rockova 2015). A companion criterion, motivated as an integral lower bound, is provided to effectively select the best recovery. The potential of the proposed procedure is demonstrated on both simulated and real high-dimensional gene expression data, which would render posterior simulation impractical.
Time and place: 4 pm on Monday, 8 February 2016, in 125 Scaife Hall

As always, the talk is free and open to the public.

Enigmas of Chance; Bayes, anti-Bayes

Posted at February 03, 2016 22:32 | permanent link

Three-Toed Sloth