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On the power of randomization for job shop scheduling with k-units length tasks
Published online by Cambridge University Press: 05 June 2008
Abstract
In the job shop scheduling problem k-units-Jm, there are
m machines and each machine has an integer processing time of at most
k time units. Each job consists of a permutation of m
tasks corresponding to all machines and thus all jobs have an identical
dilation D.
The contribution of this paper are the
following results;
(i) for $d=o(\sqrt{D})$ jobs and every fixed k, the makespan of
an optimal schedule is at most D+ o(D), which extends the result of [3]
for k=1;
(ii) a randomized on-line approximation algorithm for k-units-Jm is
presented. This is the on-line algorithm with the best known competitive
ratio against an oblivious adversary for $d = o(\sqrt{D})$
and k > 1;
(iii) different processing times yield harder instances than identical
processing times. There is no 5/3 competitive deterministic on-line
algorithm for k-units-Jm, whereas the competitive ratio of the randomized
on-line algorithm of (ii) still tends to 1 for $d = o(\sqrt{D})$
.
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- Research Article
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- Copyright
- © EDP Sciences, 2008
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