*Originally posted by: ***FoBoT**
*Originally posted by: ***oboeguy**

More than likely they use integer programming to solve massive scheduling problems. It is possible that they don't solve them exactly (IP is NP-hard).

what does that mean in layman's terms? that they might have done it for other reasons or that it is just really hard to figure out a schedule that doesn't overlap/repeat ?

In layman's terms it means that getting an optimal schedule is a hard enough problem that for a big enough delivery network (and by "big enough" I mean "most anything practically useful") we have little hope of ever being able to find the optimal routing, regardless of how fast computers get. See the movie "Sneakers" for what happens if someone figures out how to solve NP-Hard problems fast.

So what people do to solve a lot of these problems is use fairly detail-agnostic techniques to solve for "pretty good" solutions. That is to say, some of the same techniques for airline staffing and scheduling are used for FedEx routing or scheduling the NFL or running a factory, etc. Some of the "keywords" you may have heard before associated with this stuff are optimization, mathematical programming, operations researchk industrial engineering, etc.

(yes, it's my field)