Paper 4, Section II, H

Optimization
Part IB, 2019

(a) State and prove the max-flow min-cut theorem.

(b) (i) Apply the Ford-Fulkerson algorithm to find the maximum flow of the network illustrated below, where SS is the source and TT is the sink.

(ii) Verify the optimality of your solution using the max-flow min-cut theorem.

(iii) Is there a unique flow which attains the maximum? Explain your answer.

(c) Prove that the Ford-Fulkerson algorithm always terminates when the network is finite, the capacities are integers, and the algorithm is initialised where the initial flow is 0 across all edges. Prove also in this case that the flow across each edge is an integer.