Consider the flow x’ at the end of a ∆-scaling phase and let S be the set of nodes reachable
from node s in G(x’, ∆). That is, there exist flow augmenting paths from s to the nodes in S whereas there is no flow augmenting path from s to any node in S. From the definition of S, we know that the residual capacity of every arc in G(x’, ∆ ) must be less than ∆ . Thus, the residual capacity of the cut (S, S ) is at most m ∆ . In the next scaling phase, each augmentation carries at least ∆ /2 units of flow. As a result, there are at most 2m such augmentations. The labeling requires O(m) time to identify an augmenting path and push flow over the path. Therefore, the complexity is O( 2 m log U). Example: original network residual network