- INSTANCE: Graph , source , sets of terminals with node rates and edge lengths .
- SOLUTION: A tree in such that , .
- COST FUNCTION: , where (see comment).
- OBJECTIVE: Minimize.
*Approx.:*Approximable within 1.960 for the case of two non-zero rates. Approximable within 3.802 for the case of unbounded number of rates [72]. For the case of three non-zero rates, the problem admits an 1.522 approximation algorithm [89] [41].*Hardness:*NP-hard to approximate within 96/95 [36].*Comment:*are the distinct rates. For , denotes the set of all nodes with rate . The cost of an edge in the solution tree is , where (rate of edge )is the maximum rate in the component

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