I am working on a very large scheduling problem. My strategy is to limit the number of jobs to schedule to make a selection out of the whole pool of jobs in the first round, then schedule the selected jobs, and return to the first step. I realized that if I do not select more than 30-40 jobs, the optimization runs smoothly. However as I increase the number of selected jobs the optimization runs though, but several variables return the value "None". As I see their flag "Stale" is turned to TRUE.
I am quite clueless here, but first of all I would like to understand what this flag "Stale" exactly means. I hope if someone would clarify the meaning of it, it would be easier for me to hunt down my bug.
I use the "CBC" solver. I did try with other, but even with smaller sized problems they did not return an acceptable solution.
Thanks for your help in advance!
The stale flag indicates whether or not a variable's value was updated with the most recent call to a solver. If a variable's stale flag is True it usually means that the variable did not appear in any of the active model constraints that were sent to the solver.