严格的数学模型 We are now ready to define flows more formally.Let G =(V.E)be a flow network with a capacity function c.Let s be the source of the network,and let t be the sink.A flow in G is a real-valued function f:Vx V-R that satisfies the following two properties: Capacity constraint: Flow conservation:For all ue V-fs.t,we require When (u,v)E,there can be no flow from u to v,and f(u,v)=0.严格的数学模型