Abstract
We study online scheduling of unit-sized jobs in two related problems, namely, restricted assignment problem and smart grid problem. The input to the two problems are in close analogy but the objective functions are different. We show that the greedy algorithm is an optimal online algorithm for both problems. Typically, an online algorithm is proved to be an optimal online algorithm through bounding its competitive ratio and showing a lower bound with matching competitive ratio. However, our analysis does not take this approach. Instead, we prove the optimality without giving the exact bounds on competitive ratio. Roughly speaking, given any online algorithm and a job instance, we show the existence of another job instance for greedy such that (i) the two instances admit the same optimal offline schedule; (ii) the cost of the online algorithm is at least that of the greedy algorithm on the respective job instance. With these properties, we can show that the competitive ratio of the greedy algorithm is the smallest possible.
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Notes
We note that we can refer to the simulation of \(\mathcal {A}\) since \(\mathcal {A}\) is an online algorithm.
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The authors would like to thank Marcin Bienkowski for helpful discussion.
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This article belongs to the Topical Collection: Special Issue on Approximation and Online Algorithms (2019)
Guest Editors: Evripidis Bampis and Nicole Megow
This work is partially supported by Polish National Science Centre grant 2016/22/E/ST6/00499. This work is supported by Networks Sciences & Technologies(NeST), School of EEECS, University of Liverpool. This work was partially done when Hsiang-Hsuan Liu worked in Wroclaw University, Poland. A preliminary version of this paper was published in WAOA 2019 [1].
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Liu, FH., Liu, HH. & Wong, P.W.H. Greedy is Optimal for Online Restricted Assignment and Smart Grid Scheduling for Unit Size Jobs. Theory Comput Syst 65, 1009–1032 (2021). https://doi.org/10.1007/s00224-021-10037-w
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DOI: https://doi.org/10.1007/s00224-021-10037-w