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Poster

Exploiting Numerical Sparsity for Efficient Learning : Faster Eigenvector Computation and Regression

Neha Gupta · Aaron Sidford

Room 210 #58

Keywords: [ Regression ] [ Components Analysis (e.g., CCA, ICA, LDA, PCA) ]


Abstract: In this paper, we obtain improved running times for regression and top eigenvector computation for numerically sparse matrices. Given a data matrix \matA\Rn×d where every row a\Rd has a22L and numerical sparsity s, i.e. a12/a22s, we provide faster algorithms for these problems for many parameter settings. For top eigenvector computation, when \gap>0 is the relative gap between the top two eigenvectors of \matA\matA and r is the stable rank of \matA we obtain a running time of \otilde(nd+r(s+rs)/\gap2) improving upon the previous best unaccelerated running time of O(nd+rd/\gap2). As rd and sd our algorithm everywhere improves or matches the previous bounds for all parameter settings. For regression, when μ>0 is the smallest eigenvalue of \matA\matA we obtain a running time of \otilde(nd+(nL/μ)snL/μ) improving upon the previous best unaccelerated running time of \otilde(nd+nLd/μ). This result expands when regression can be solved in nearly linear time from when L/μ=\otilde(1) to when L/μ=\otilde(d2/3/(sn)1/3). Furthermore, we obtain similar improvements even when row norms and numerical sparsities are non-uniform and we show how to achieve even faster running times by accelerating using approximate proximal point \cite{frostig2015regularizing} / catalyst \cite{lin2015universal}. Our running times depend only on the size of the input and natural numerical measures of the matrix, i.e. eigenvalues and p norms, making progress on a key open problem regarding optimal running times for efficient large-scale learning.

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