Extended Hardness Results for Approximate Gröbner Basis Computation
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Two models were recently proposed to explore the robust hardness of Gröbner basis computation. Given a polynomial system, both models allow an algorithm to selectively ignore some of the polynomials: the algorithm is only responsible for returning a Gröbner basis for the ideal generated by the remaining polynomials. For the q-Fractional Gröbner Basis Problem the algorithm is allowed to ignore a constant (1-q)-fraction of the polynomials (subject to one natural structural constraint). Here we prove a new strongest-parameter result: even if the algorithm is allowed to choose a (3/10-ϵ)-fraction of the polynomials to ignore, and need only compute a Gröbner basis with respect to some lexicographic order for the remaining polynomials, this cannot be accomplished in polynomial time (unless P=NP). This statement holds even if every polynomial has maximum degree 3. Next, we prove the first robust hardness result for polynomial systems of maximum degree 2: for the q-Fractional model a (1/5-ϵ) fraction of the polynomials may be ignored without losing provable NP-Hardness. Both theorems hold even if every polynomial contains at most three distinct variables. Finally, for the Strong c-partial Gröbner Basis Problem of De Loera et al. we give conditional results that depend on famous (unresolved) conjectures of Khot and Dinur, et al.
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