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A lower bound on the MOD 6 degree of the OR function. (English) Zbl 0936.68051

Summary: We examine the computational power of modular counting, where the modulus \(m\) is not a prime power, in the setting of polynomials in Boolean variables over \(Z_m\). In particular, we say that a polynomial \(P\) weakly represents a Boolean function \(f\) (both have \(n\) variables) if for any inupts \(x\) and \(y\) in \(\{0,1\}^n\), we have \(P(x)\neq P(y)\) whenever \(f(x)\neq f(y)\). D. A. M. Barrington, R. Beigel and S. Rudich [Comput. Complexity 4, No. 4, 367-382 (1994; Zbl 0829.68057)] investigated the minimal degree of a polynomial representing the OR function in this way, proving an upper bound of \(O(n^{1/r})\) (where \(r\) is the number of distinct primes dividing \(m\)) and a lower bound of \(\omega(1)\). Here, we show a lower bound of \(\Omega(\log n)\) when \(m\) is a product of two primes and \(\Omega((\log n)^{1/(r- 1)})\) in general. While many lower bounds are known for a much stronger form of representation of a function by a polynomial, very little is known using this liberal (and, we argue, more natural) definition. While the degree is known to be \(\Omega(\log n)\) for the generalized inner product because of its high communication complexity, our bound is the best known for any function of low communication complexity and any modulus not a prime power.

MSC:

68Q15 Complexity classes (hierarchies, relations among complexity classes, etc.)
68Q25 Analysis of algorithms and problem complexity

Citations:

Zbl 0829.68057
Full Text: DOI