Computation of the Reverse Shortest-Path Problem

The shortest-path problem in a network is to find shortest paths between some specified sources and terminals when the lengths of edges are given. This paper studies a reverse problem: how to shorten the lengths of edges with as less cost as possible such that the distances between specified sources and terminals are reduced to the required bounds. This can be regarded as a routing speed-up model in transportation networks. In this paper, for the general problem, the NP-completeness is shown, and for the case of trees and the case of single source-terminal, polynomial-time algorithms are presented.