In this post I will briefly describe one type of algorithm that has been used to solve the well-known max flow problem. This problem is essentially how to find the maximum flow that can be sent from a source node to a sink node in a network. Think of a graph connected with nodes and arcs each having a certain capacity or limit of flow that it can hold. This could be a very literal thing such as network of pipes or internet cables, but other stranger uses for network flow problems do exist such as the baseball elimination problem I talked about before.

### Residual Capacities

The augmenting path algorithm utilises ideas in capacitated graphs called the residual capacity and the residual flow. This is the potential for flow to move along particular arcs. It can be summed up as Residual Flow = Capacity – Forwards Flow + Backwards Flow. See the diagram below to see how it works (the first number is the flow, the second the capacity).

Residual capacities

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