| | The complexity of the covering radius problem on lattices and codes (Site not responding. Last check: 2007-10-10) |
 | | For the covering radius on n-dimensional lattices, we show that the problem can be approximated within any constant factor gamma(n) > 1 in random exponential time 2^{O(n)}, it is in AM for gamma(n) = 2, in coAM for gamma(n) = sqrt{n / log n}, and in NP intersected coNP for gamma(n) = sqrt{n}. |
 | | For the covering radius on n-dimensional linear codes, we show that the problem can be solved in deterministic polynomial time for approximation factor gamma(n) = log n, but cannot be solved in polynomial time for some gamma(n) = Omega(log log n) unless NP can be simulated in deterministic n^{O(log log log n)} time. |
 | | Moreover, we prove that the problem is NP-hard for any constant approximation factor, it is Pi_2-hard for some constant approximation factor, and it is in AM for approximation factor 2. |
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