Communication lower bounds using directional derivatives

  • Authors:
  • Alexander A. Sherstov

  • Affiliations:
  • University of California, Los Angeles, Los Angeles, CA, USA

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

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Abstract

We study the set disjointness problem in the most powerful bounded-error model: the number-on-the-forehead model with k parties and arbitrary classical or quantum communication. We obtain a communication lower bound of Omega(√(n)/2k*k) bits, which is essentially optimal. Proving it was a longstanding open problem even in restricted settings, such as one-way classical protocols with k=4 parties (Wigderson 1997). The proof contributes a novel technique for lower bounds on multiparty communication, based on directional derivatives of communication protocols over the reals.