Level of Repair Analysis and Minimum Cost Homomorphisms of Graphs

  • Gregory Gutin
  • Arash Rafiey
  • Anders Yeo
  • Michael Tso
Part of the Lecture Notes in Computer Science book series (LNCS, volume 3521)


Level of Repair Analysis (LORA) is a prescribed procedure for defence logistics support planning. For a complex engineering system containing perhaps thousands of assemblies, sub-assemblies, components, etc. organized into several levels of indenture and with a number of possible repair decisions, LORA seeks to determine an optimal provision of repair and maintenance facilities to minimize overall life-cycle costs. For a LORA problem with two levels of indenture with three possible repair decisions, which is of interest in UK and US military and which we call LORA-BR, Barros (1998) and Barros and Riley (2001) developed certain branch-and-bound heuristics. The surprising result of this paper is that LORA-BR is, in fact, polynomial-time solvable. To obtain this result, we formulate the general LORA problem as an optimization homomorphism problem on bipartite graphs, and reduce a generalization of LORA-BR, LORA-M, to the maximum weight independent set problem on a bipartite graph. We prove that the general LORA problem is NP-hard by using an important result on list homomorphisms of graphs. We introduce the minimum cost graph homomorphism problem and provide partial results. Finally, we show that our result for LORA-BR can be applied to prove that an extension of the maximum weight independent set problem on bipartite graphs is polynomial time solvable.


Polynomial Time Bipartite Graph Interval Graph Input Graph Complex Engineering System 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer-Verlag Berlin Heidelberg 2005

Authors and Affiliations

  • Gregory Gutin
    • 1
  • Arash Rafiey
    • 1
  • Anders Yeo
    • 1
  • Michael Tso
    • 2
  1. 1.Department of Computer ScienceRoyal Holloway University of LondonEghamUK
  2. 2.School of MathematicsUniversity of ManchesterManchesterUK

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