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Optimal bounds for sign-representing the intersection of two halfspaces by polynomials

Published: 05 June 2010 Publication History

Abstract

The threshold degree of a function f:{0,1}n->{-1,+1} is the least degree of a real polynomial p with f=sgn p. We prove that the intersection of two halfspaces on {0,1}n has threshold degree Omega(n), which matches the trivial upper bound and completely answers a question due to Klivans (2002). The best previous lower bound was Omega(sqrt n). Our result shows that the intersection of two halfspaces on {0,1}n only admits a trivial 2Θ(n)-time learning algorithm based on sign-representation by polynomials, unlike the advances achieved in PAC learning DNF formulas and read-once Boolean formulas. The proof introduces a new technique of independent interest, based on Fourier analysis and matrix theory.

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    cover image ACM Conferences
    STOC '10: Proceedings of the forty-second ACM symposium on Theory of computing
    June 2010
    812 pages
    ISBN:9781450300506
    DOI:10.1145/1806689
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    Published: 05 June 2010

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    Author Tags

    1. halfspaces
    2. intersections of halfspaces
    3. pac learning
    4. polynomial representations of boolean functions

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    STOC'10: Symposium on Theory of Computing
    June 5 - 8, 2010
    Massachusetts, Cambridge, USA

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    Cited By

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    • (2015)Hardness Amplification and the Approximate Degree of Constant-Depth CircuitsAutomata, Languages, and Programming10.1007/978-3-662-47672-7_22(268-280)Online publication date: 20-Jun-2015
    • (2014)Breaking the minsky-papert barrier for constant-depth circuitsProceedings of the forty-sixth annual ACM symposium on Theory of computing10.1145/2591796.2591871(223-232)Online publication date: 31-May-2014
    • (2012)Making polynomials robust to noiseProceedings of the forty-fourth annual ACM symposium on Theory of computing10.1145/2213977.2214044(747-758)Online publication date: 19-May-2012
    • (2010)A random-sampling-based algorithm for learning intersections of halfspacesJournal of the ACM10.1145/1857914.185791657:6(1-14)Online publication date: 5-Nov-2010
    • (2010)New Upper Bounds on the Average PTF Density of Boolean FunctionsAlgorithms and Computation10.1007/978-3-642-17517-6_28(304-315)Online publication date: 2010

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