Optimal bounds for monotonicity and lipschitz testing over hypercubes and hypergrids

  • Authors:
  • Deeparnab Chakrabarty;C. Seshadhri

  • Affiliations:
  • Microsoft Research India, Bengaluru, India;Sandia National Laboratories, Livermore, CA, USA

  • Venue:
  • Proceedings of the forty-fifth annual ACM symposium on Theory of computing
  • Year:
  • 2013

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Abstract

The problem of monotonicity testing over the hypergrid and its special case, the hypercube, is a classic question in property testing. We are given query access to f:[k]n - R (for some ordered range R). The hypergrid/cube has a natural partial order given by coordinate-wise ordering, denoted by prec. A function is monotone if for all pairs x prec y, f(x) ≤ f(y). The distance to monotonicity, εf, is the minimum fraction of values of f that need to be changed to make f monotone. For k=2 (the boolean hypercube), the usual tester is the edge tester, which checks monotonicity on adjacent pairs of domain points. It is known that the edge tester using O(ε-1n log|R|) samples can distinguish a monotone function from one where εf ε. On the other hand, the best lower bound for monotonicity testing over general R is Ω(n). We resolve this long standing open problem and prove that O(n/ε) samples suffice for the edge tester. For hypergrids, known testers require O(ε-1n log k log |R|) samples, while the best known (non-adaptive) lower bound is Ω(ε-1 n log k). We give a (non-adaptive) monotonicity tester for hypergrids running in O(ε{-1} n log k) time. Our techniques lead to optimal property testers (with the same running time) for the natural Lipschitz property on hypercubes and hypergrids. (A c-Lipschitz function is one where |f(x) - f(y)| ≤ c||x-y||1.) In fact, we give a general unified proof for O(ε-1nlog k)-query testers for a class of "bounded-derivative" properties, a class containing both monotonicity and Lipschitz.