Driving through an unfamiliar city centre recently, with its poorly signposted routes and confusing one-way systems, I became increasingly frustrated and completely lost. Sometimes I went with the flow and took the direction being followed by the majority of the traffic; at other times I deliberately avoided such directions. I began to feel like a particle randomly diffusing through an incomprehensible network of roads! When I eventually reached my destination and regained my equilibrium I realised the process I'd followed through the streets reminded me of a technique for solving linear networks that I've only come across in the relatively recent past.
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