On this basis, in order to minimize the two objectives of the transport costs to model, to convert it into a network flow model with a stratified, with the minimum cost maximum flow algorithm.

If an edge in a network is destroyed, the value of maximum flow between two vertices in the network is decreased in general.

If the decrease of the value of maximum flow by the destruction is large, the degree of influence of the edge on the vulnerability of the network is considered to be large.