title: Dijkstra's algorithm cannot deal with negative weights, when do you see negative weights in the real world?
body: <p>I can't think of a concrete instance in which you'd have a negative weight. You cannot have a negative distance between two houses, you cannot go back in time. When would you have a graph with a negative edge weight?</p>
  
  <p>I found the Bellman Ford algorithm was originally used to deal with routing in ARPANET, but again, can't imagine where you'd run into a route with a negative weight, it just doesn't seem possible. I could just be thinking too hard about this, what would be a simple example?</p>