I have a location problem I need help with:
Suppose a boat company wants to operate services between 11 ports in a city. The number of return journeys between port i and port j is denoted by a x-variable (Xij), i and j = 1 to 11. Now I need to impose a constraint such that the number of return journeys between the same pair of ports does not exceed 3. That is, e.g. there can be at most 3 return journeys made between port 1 and port 2.
I know I can do it by Xij + Xji <= 3, but this would result in tons of constraints...
Can anyone come up with a compact form of this constraint? Thank you in advance!