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| Content Provider | Society for Industrial and Applied Mathematics (SIAM) |
|---|---|
| Author | Drineas, Petros Mahoney, Michael W. Meng, Xiangrui Woodruff, David P. Magdon-Ismail, Malik Clarkson, Kenneth L. |
| Copyright Year | 2016 |
| Abstract | We provide fast algorithms for overconstrained $\ell_p$ regression and related problems: for an $n\times d$ input matrix $A$ and vector $b\in\mathbb{R}^n$, in $O(nd\log n)$ time we reduce the problem $\min_{x\in\mathbb{R}^d} \|Ax-b\|_p$ to the same problem with input matrix $\tilde A$ of dimension $s \times d$ and corresponding $\tilde b$ of dimension $s\times 1$. Here, $\tilde A$ and $\tilde b$ are a coreset for the problem, consisting of sampled and rescaled rows of $A$ and $b$; and $s$ is independent of $n$ and polynomial in $d$. Our results improve on the best previous algorithms when $n\gg d$ for all $p\in [1,\infty)$ except $p=2$; in particular, they improve the $O(nd^{1.376+})$ running time of Sohler and Woodruff [Proceedings of the 43rd Annual ACM Symposium on Theory of Computing, 2011, pp. 755--764] for $p=1$, which uses asymptotically fast matrix multiplication, and the $O(nd^5\log n)$ time of Dasgupta et al. [SIAM J. Comput., 38 (2009), pp. 2060--2078] for general $p$, which uses ellipsoidal rounding. We also provide a suite of improved results for finding well-conditioned bases via ellipsoidal rounding, illustrating tradeoffs between running time and conditioning quality, including a one-pass conditioning algorithm for general $\ell_p$ problems. To complement this theory, we provide a detailed empirical evaluation of implementations of our algorithms for $p=1$, comparing them with several related algorithms. Among other things, our empirical results clearly show that, in the asymptotic regime, the theory is a very good guide to the practical performance of these algorithms. Our algorithms use our faster constructions of well-conditioned bases for $\ell_p$ spaces and, for $p=1$, a fast subspace embedding of independent interest that we call the Fast Cauchy transform: a distribution over matrices $\Pi: \mathbb{R}^n\mapsto \mathbb{R}^{O(d\log d)}$, found obliviously to $A$, that approximately preserves the $\ell_1$ norms, that is, with large probability, simultaneously for all $x$, $\|Ax\|_1 \approx \|\Pi Ax\|_1$, with distortion $O(d^{2+\eta} )$, for an arbitrarily small constant $\eta>0$; and, moreover, $\Pi A$ can be computed in $O(nd\log d)$ time. The techniques underlying our Fast Cauchy transform include Fast Johnson--Lindenstrauss transforms, low-coherence matrices, and rescaling by Cauchy random variables. |
| Starting Page | 763 |
| Ending Page | 810 |
| Page Count | 48 |
| File Format | |
| ISSN | 00975397 |
| DOI | 10.1137/140963698 |
| e-ISSN | 10957111 |
| Journal | SIAM Journal on Computing (SMJCAT) |
| Issue Number | 3 (Special Section on the Fifty-Fourth Annual IEEE Symposium on Foundations of Computer Science (FOCS 2013)) |
| Volume Number | 45 |
| Language | English |
| Publisher | Society for Industrial and Applied Mathematics |
| Publisher Date | 2016-06-15 |
| Access Restriction | Subscribed |
| Subject Keyword | Cauchy transform subspace embedding randomized algorithms robust regression Randomized algorithms |
| Content Type | Text |
| Resource Type | Article |
| Subject | Mathematics Computer Science |
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