Optimal bounds for decision problems on the CRCW PRAM

  • Authors:
  • P. Beame;J. Hastad

  • Affiliations:
  • Laboratory for Computer Science, Massachusetts Institute of Technology, 545 Technology Square, Cambridge, MA;Laboratory for Computer Science, Massachusetts Institute of Technology, 545 Technology Square, Cambridge, MA

  • Venue:
  • STOC '87 Proceedings of the nineteenth annual ACM symposium on Theory of computing
  • Year:
  • 1987

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Abstract

We prove optimal &OHgr;(log n/log log n) lower bounds on the time for CRCW PRAM's with polynomially bounded numbers of processors or memory cells to compute parity and a number of related problems. We also exhibit a strict time hierarchy of explicit Boolean functions of n bits on such machines which holds up to &Ogr;(log n/log log n) time. Furthermore, we show that almost all Boolean functions of n bits require log n - log log n + &OHgr;(1) time when the number of processors is at most polynomial in n. Our bounds do not place restrictions on the uniformity of the algorithms nor on the instruction sets of the machines.