You have an either/or constraint, and I do not think you can use a direct or
statement (unless developers made something like that).
Usually, if you have an either/or constraint, you should define a binary
variable, say y, taking only 0-1 value. If y=0, the sum is less than zero,
if y=1, the sum
Hello Eduardo,
I found the following paper to be insightful for finding
better formulations:
Norbert Ascheuer, Matteo Fischetti, Martin Grötschel
Solving the Asymmetric Travelling Salesman Problem with Time Windows by
Branch-and-Cut
Appeared in: Math. Program., Ser. A, Vol 90, No 3: 475-506
