Unconstrained submodular maximization captures many NP-hard combinatorial optimization problems, including Max-Cut, Max-Di-Cut, and variants of facility location problems. Recently, Buchbinder et al. presented a surprisingly simple linear time randomized greedy-like online algorithm that achieves a constant approximation ratio of 1/2, matching optimally the hardness result of Feige et al.. Motivated by the algorithm of Buchbinder et al., we introduce a precise algorithmic model called double-sided myopic algorithms. We show that while the algorithm of Buchbinder et al. can be realized as a randomized online double-sided myopic algorithm, no such deterministic algorithm, even with adaptive ordering, can achieve the same approximation ratio. With respect to the Max-Di-Cut problem, we relate the Buchbinder et al. algorithm and our myopic framework to the online algorithm and inapproximation of Bar-Noy and Lampis.

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