One April afternoon in 2003, a reclusive Russian mathematician -- his hair overgrown, his beard and nails untrimmed for ages -- arrived at the Massachusetts Institute of Technology to deliver a talk.

Imagine walking into a math classroom. Everything is quiet, students are diligently writing and reading and thinking. You hear the rustle of paper, scratching pens, and the occasional student shifting ...

One of the most classic algorithmic problems deals with calculating the shortest path between two points. A more complicated variant of the problem is when the route traverses a changing network - ...