The fast johnson-lindenstrauss transform and approximate nearest neighbors

Nir Ailon, Bernard Chazelle

Research output: Contribution to journalArticlepeer-review

295 Scopus citations


We introduce a new low-distortion embedding of l 2 d l p O(log n (p = 1, 2) called the fast Johnson-Lindenstrauss transform (FJLT). The FJLT is faster than standard random projections and just as easy to implement. It is based upon the preconditioning of a sparse projection matrix with a randomized Fourier transform. Sparse random projections are unsuitable for low-distortion embeddings. We overcome this handicap by exploiting the "Heisenberg principle" of the Fourier transform, i.e., its local-global duality. The FJLT can be used to speed up search algorithms based on low-distortion embeddings in l 1 and l 2. We consider the case of approximate nearest neighbors in l 2 d. We provide a faster algorithm using classical projections, which we then speed up further by plugging in the FJLT. We also give a faster algorithm for searching over the hypercube.

Original languageEnglish (US)
Pages (from-to)302-322
Number of pages21
JournalSIAM Journal on Computing
Issue number1
StatePublished - 2009
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General Computer Science
  • General Mathematics


  • Approximate nearest neighbors
  • Dimension reduction
  • Random matrices


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