2016/09/07 by Larsen, Kasper Green, Nelson, Jelani · 7 citations
#Computational Geometry (cs.CG) #Data Structures and Algorithms (cs.DS) #FOS: Computer and information sciences #FOS: Mathematics #Functional Analysis (math.FA) #Information Theory (cs.IT)
paper · doi:10.48550/arxiv.1609.02094
For any integers d, n ≥ 2 and 1/(min\n,d\)0.4999 < ε<1, we show the existence of a set of n vectors X⊂ ℝd such that any embedding f:X→ ℝm satisfying ∀ x,y∈ X, (1-ε)‖x-y‖22≤ ‖f(x)-f(y)‖22 ≤ (1+ε)‖x-y‖22 must have m = Ω(ε-2 \lg n). This lower bound matches the upper bound given by the Johnson-Lindenstrauss lemma [JL84]. Furthermore, our lower bound holds for nearly the full range of ε of interest, since there is always an isometric embedding into dimension min\d, n\ (either the identity map, or projection onto \mathopspan(X)). Previously such a lower bound was only known to hold against linear maps f, and not for such a wide range of parameters ε, n, d [LN16]. The best previously known lower bound for general f was m = Ω(ε-2\lg n/\lg(1/ε)) [Wel74, Lev83, Alo03], which is suboptimal for any ε = o(1).