On variants of the Johnson–Lindenstrauss lemma

The Johnson–Lindenstrauss lemma asserts that an n‐point set in any Euclidean space can be mapped to a Euclidean space of dimension k = O(ε‐2 log n) so that all distances are preserved up to a multiplicative factor between 1 − ε and 1 + ε. Known proofs obtain such a mapping as a linear map Rn → Rk with a suitable random matrix. We give a simple and self‐contained proof of a version of the Johnson–Lindenstrauss lemma that subsumes a basic versions by Indyk and Motwani and a version more suitable for efficient computations due to Achlioptas. (Another proof of this result, slightly different but in a similar spirit, was given independently by Indyk and Naor.) An even more general result was established by Klartag and Mendelson using considerably heavier machinery.