If there exists some 𝐪\mathbf{q} with ||𝐪−𝐲||0≤R||\mathbf{q}-\mathbf{y}||_0 \leq R, return a vector 𝐪~\tilde{\mathbf{q}} with ||𝐪~−𝐲||0≤C⋅R||\tilde{\mathbf{q}}-\mathbf{y}||_0 \leq C \cdot R in:

  • Time: O(n1/C)O(n^{1/C})
  • Space: O(n1+1/C)O(n^{1+1/C})

where ||𝐪−𝐲||0||\mathbf{q}-\mathbf{y}||_0 is the “hamming distance” number of elements that different between 𝐪\mathbf{q} and 𝐲\mathbf{y}.

Used in near neighbor search problem.

#incomplete


Given a (r1,r2,p1,p2)(r_1,r_2,p_1,p_2)-locality sensitive hash family, (r1,r2)(r_1,r_2)-PLEB (point location in equal balls) can be solved with constant probability using:

  • Space: O(dn+n1+γ)O(dn + n^{1+\gamma})
  • Query time: O(nγ)O(n^\gamma) hash function evaluations and metric computations, d(⋅,⋅)d(\cdot,\cdot), where γ=log⁡(1/p1)log⁡(1/p2)\gamma = \frac{\log(1/p_1)}{\log(1/p_2)}.

PLEB (point location in equal balls)
For given radii r1, r2 with r1 ≤ r2, if there is at least one point p ∈ X with d(q, p) ≤ r1, return any p with d(q, p) < r2. On the other hand, if there is no point p ∈ X with d(q, p) < r2, output FAIL.


References:

  1. P. Indyk and R. Motwani, “Approximate nearest neighbors: towards removing the curse of dimensionality,” in Proceedings of the thirtieth annual ACM symposium on Theory of computing  - STOC ’98, Dallas, Texas, United States: ACM Press, 1998, pp. 604–613. doi: 10.1145/276698.276876.
  2. https://www.cs.princeton.edu/courses/archive/fall18/cos521/Lectures/lec12.pdf