Approximating Capacitated Tree-Routings in Networks

  • Ehab Morsy
  • Hiroshi Nagamochi
Part of the Lecture Notes in Computer Science book series (LNCS, volume 4484)


The capacitated tree-routing problem (CTR) in a graph G = (V,E) consists of an edge weight function w:ER  + , a sink s ∈ V, a terminal set M ⊆ V with a demand function q:MR  + , a routing capacity κ> 0, and an integer edge capacity λ ≥ 1. The CTR asks to find a partition \({\cal M}=\{Z_{1},Z_{2},\ldots,Z_{\ell}\}\) of M and a set \({\cal T}=\{T_{1},T_{2},\ldots,T_{\ell}\}\) of trees of G such that each T i spans Z i  ∪ {s} and satisfies \(\sum_{v\in Z_{i}}q(v)\leq \kappa\). A subset of trees in \({\cal T}\) can pass through a single copy of an edge e ∈ E as long as the number of these trees does not exceed the edge capacity λ; any integer number of copies of e are allowed to be installed, where the cost of installing a copy of e is w(e). The objective is to find a solution \(({\cal M}, {\cal T})\) that minimizes the installing cost \(\sum_{e\in E} \lceil |\{T\in {\cal T}\mid T \mbox{ contains }e\}| /\lambda \rceil w(e)\). In this paper, we propose a \((2+\rho_{\mbox{\tiny{\sc ST}}})\)-approximation algorithm to the CTR, where \(\rho_{\mbox{\tiny{\sc ST}}}\) is any approximation ratio achievable for the Steiner tree problem.


Approximation Algorithm Graph Algorithm Routing Problems Network Optimization Tree Cover 


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Copyright information

© Springer-Verlag Berlin Heidelberg 2007

Authors and Affiliations

  • Ehab Morsy
    • 1
  • Hiroshi Nagamochi
    • 1
  1. 1.Department of Applied Mathematics and Physics, Graduate School of Informatics, Kyoto University, Yoshida Honmachi, Sakyo, Kyoto 606-8501Japan

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