A Faster Combinatorial Approximation Algorithm for Scheduling Unrelated Parallel Machines

  • Martin Gairing
  • Burkhard Monien
  • Andreas Woclaw
Part of the Lecture Notes in Computer Science book series (LNCS, volume 3580)


We consider the problem of scheduling n independent jobs on m unrelated parallel machines without preemption. Job i takes processing time p ij on machine j, and the total time used by a machine is the sum of the processing times for the jobs assigned to it. The objective is to minimize makespan. The best known approximation algorithms for this problem compute an optimum fractional solution and then use rounding techniques to get an integral 2-approximation.

In this paper we present a combinatorial approximation algorithm that matches this approximation quality. It is much simpler than the previously known algorithms and its running time is better. This is the first time that a combinatorial algorithm always beats the interior point approach for this problem. Our algorithm is a generic minimum cost flow algorithm, without any complex enhancements, tailored to handle unsplittable flow. It pushes unsplittable jobs through a two-layered bipartite generalized network defined by the scheduling problem. In our analysis, we take advantage from addressing the approximation problem directly. In particular, we replace the classical technique of solving the LP-relaxation and rounding afterwards by a completely integral approach. We feel that this approach will be helpful also for other applications.


Schedule Problem Approximation Algorithm Generalize Maximum Unrelated Parallel Machine Generalize Assignment Problem 
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Copyright information

© Springer-Verlag Berlin Heidelberg 2005

Authors and Affiliations

  • Martin Gairing
    • 1
  • Burkhard Monien
    • 1
  • Andreas Woclaw
    • 1
  1. 1.Faculty of Computer Science, Electrical Engineering and MathematicsUniversity of PaderbornPaderbornGermany

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