Abstract
In 1997, Håstad showed NP-hardness of (1 − ϵ, 1/q + δ)-approximating Max-3Lin(Zq); however, it was not until 2007 that Guruswami and Raghavendra were able to show NP-hardness of (1 − ϵ, δ)-approximating Max-3Lin(Z). In 2004, Khot--Kindler--Mossel--O’Donnell showed UG-hardness of (1 − ϵ, δ)-approximating Max-2Lin(Zq) for q = q(ϵ, δ) a sufficiently large constant; however, achieving the same hardness for Max-2Lin(Z) was given as an open problem in Raghavendra’s 2009 thesis. In this work, we show that fairly simple modifications to the proofs of the Max-3Lin(Zq) and Max-2Lin(Zq) results yield optimal hardness results over Z. In fact, we show a kind of “bicriteria” hardness: Even when there is a (1 − ϵ)-good solution over Z, it is hard for an algorithm to find a δ-good solution over Z, R, or Zm for any m ⩾ q(ϵ, δ) of the algorithm’s choosing.
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Index Terms
Hardness of Max-2Lin and Max-3Lin over Integers, Reals, and Large Cyclic Groups
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