The query complexity of finding local minima in the lattice

  • Authors:
  • Amos Beimel;Felix Geller;Eyal Kushilevitz

  • Affiliations:
  • Ben-Gurion Univ., Beer-Sheva, Israel;Technion, Haifa, Israel;Technion, Haifa, Israel

  • Venue:
  • Information and Computation
  • Year:
  • 2001

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Abstract

In this paper we study the query complexity of finding local minimum points of a boolean function. This task occurs frequently in exact learning algorithms for many natural classes, such as monotone DNF, O (log n)-term DNF, unate DNF, and decision trees. On the negative side, we prove that any (possibly randomized) algorithm that produces a local minimum of a function f chosen from a sufficiently "rich" concept class, using a membership oracle for f, must ask (n2) membership queries in the worst case. In particular, this lower bound applies to the class of decision trees. A simple algorithm is known that achieves this lower bound. On the positive side, we show that for the class O (log n)-term DNF finding local minimum points requires only (n log n) membership queries (and more generally (tn) membership queries for t-term DNF with tn). This efficient procedure improves the time and query complexity of known learning algorithms for the class O (log n)-term DNF. 2001 Elsevier Science.