Choosing, Agreeing, and Eliminating in Communication Complexity

  • Authors:
  • Amos Beimel;Sebastian Ben Daniel;Eyal Kushilevitz;Enav Weinreb

  • Affiliations:
  • Department of Computer Science, Ben Gurion University of the Negev, Beer Sheva, Israel;Department of Computer Science, Ben Gurion University of the Negev, Beer Sheva, Israel;Department of Computer Science, Technion, Haifa, Israel;Department of Computer Science, Technion, Haifa, Israel

  • Venue:
  • Computational Complexity
  • Year:
  • 2014

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Abstract

We consider several questions inspired by the direct-sum problem in (two-party) communication complexity. In all questions, there are k fixed Boolean functions f 1,驴,f k and each of Alice and Bob has k inputs, x 1,驴,x k and y 1,驴,y k , respectively. In the eliminate problem, Alice and Bob should output a vector 驴1,驴,驴 k such that f i (x i , y i ) 驴 驴 i for at least one i (i.e., their goal is to eliminate one of the 2 k output vectors); in the choose problem, Alice and Bob should return (i, f i (x i , y i )), for some i (i.e., they choose one instance to solve), and in the agree problem they should return f i (x i , y i ), for some i (i.e., if all the k Boolean values agree then this must be the output). The question, in each of the three cases, is whether one can do better than solving one (say, the first) instance. We study these three problems and prove various positive and negative results. In particular, we prove that the randomized communication complexity of eliminate, of k instances of the same function f, is characterized by the randomized communication complexity of solving one instance of f.