Polynomial threshold functions, AC functions and spectrum norms

  • Authors:
  • J. Bruck;R. Smolensky

  • Affiliations:
  • IBM Almaden Res. Center, San Jose, CA, USA;-

  • Venue:
  • SFCS '90 Proceedings of the 31st Annual Symposium on Foundations of Computer Science
  • Year:
  • 1990

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Abstract

The class of polynomial-threshold functions is studied using harmonic analysis, and the results are used to derive lower bounds related to AC/sup 0/ functions. A Boolean function is polynomial threshold if it can be represented as a sign function of a sparse polynomial (one that consists of a polynomial number of terms). The main result is that polynomial-threshold functions can be characterized by means of their spectral representation. In particular, it is proved that a Boolean function whose L/sub 1/ spectral norm is bounded by a polynomial in n is a polynomial-threshold function, and that a Boolean function whose L/sub infinity //sup -1/ spectral norm is not bounded by a polynomial in n is not a polynomial-threshold function. Some results for AC/sup 0/ functions are derived.