2009/01/01 by Nir Ailon, Bernard Chazelle · 52 citations
Engineering · Computer Science · #Sparse and Compressive Sensing Techniques #Advanced Image and Video Retrieval Techniques #Computational Geometry and Mesh Generation
paper · doi:10.1137/060673096
We introduce a new low-distortion embedding of ℓ2d into ℓpO(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 ℓ1 and ℓ2. We consider the case of approximate nearest neighbors in ℓ2d. 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.