Direct product via round-preserving compression

  • Authors:
  • Mark Braverman;Anup Rao;Omri Weinstein;Amir Yehudayoff

  • Affiliations:
  • Princeton University;University of Washington;Princeton University;Technion IIT, Israel

  • Venue:
  • ICALP'13 Proceedings of the 40th international conference on Automata, Languages, and Programming - Volume Part I
  • Year:
  • 2013

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Abstract

We obtain a strong direct product theorem for two-party bounded round communication complexity. Let sucr(μ,f,C) denote the maximum success probability of an r-round communication protocol that uses at most C bits of communication in computing f(x,y) when (x,y)~μ. Jain et al. [12] have recently showed that if ${\sf suc}_{r}(\mu,f,C) \leq \frac{2}{3}$ and $T\ll (C-\Omega (r^2)) \cdot\frac{n}{r}$, then ${\sf suc}_r(\mu^n,f^n,T)\leq \exp(-\Omega(n/r^2))$. Here we prove that if ${\sf suc}_{7r}(\mu,f,C) \leq \frac{2}{3}$ and T≪(C−Ω(r logr)) ·n then ${\sf suc}_{r}(\mu^n,f^n,T)\leq\exp(-\Omega(n))$. Up to a logr factor, our result asymptotically matches the upper bound on suc7r(μn,fn,T) given by the trivial solution which applies the per-copy optimal protocol independently to each coordinate. The proof relies on a compression scheme that improves the tradeoff between the number of rounds and the communication complexity over known compression schemes.