A Nonlinear Approach to Dimension Reduction

The l(2) flattening lemma of Johnson and Lindenstrauss (in: Proceedings of the conference in modern analysis and probability, 1984) is a powerful tool for dimension reduction. It has been conjectured that the target dimension bounds can be refined and bounded in terms of the intrinsic dimensionality of the dataset (for example, the doubling dimension). One such problem was proposed by Lang and Plaut (Geom Dedicata 87(1-3):285-307, 2001) (see also Abraham et al. in: Proceedings of the 20th annual ACM-SIAM symposium on discrete algorithms, 2008; Chan et al. in: J ACM 57(4):1-26, 2010; Gupta et al. in: Proceedings of the 44th annual IEEE symposium on foundations of computer science, 2003; Matousek in: Open problems on low-distortion embeddings of finite metric spaces, 2002), and is still open. We prove another result in this line of work: The snowflake metric d(alpha) (alpha < 1) of a doubling set S subset of l(2) embeds with constant distortion into l(2)(D) for dimension D that depends solely on the doubling constant of the metric. In fact, the distortion can be made arbitrarily close to 1, and the target dimension is polylogarithmic in the doubling constant. Our techniques are robust and extend to the more difficult space l(1), although the dimension bounds here are quantitatively inferior to those for l(2).