[Cbc] Making CBC run faster

[Mona Rahn]

Hi all,

I am trying to program software for automated roster planning. My program
works fine if I use CPLEX, but the final goal is to use CBC (or some other
free solver). I have several cases which CPLEX solves in about half a
minute, while CBC is still not done after 10 minutes.

Do you have a tip how to make CBC run faster? I.e., is it better to add
constraints / variables? Or to remove them? Or can I influence the solver
in any other way? Or is there another free solver which might run faster?

Here are some  more details about the model: I use MIPs,

   - the variables are essentially binary variables, one for each tuple
   (worker, time, task)
   - the constraints consist of
      - the intuitive roster constraints such as "there is at most one task
      for each worker at each time", "each task must be executed by exactly one
      worker", etc.
      - additional constraints such as "for every worker, Task X must take
      at most 30% of his time" (where Task X is some unpleasant task)
      - additional constraints such as "after doing Task X, every worker
      has to take a break", "Task Y is forbidden after Task X"
   - the objective function - which is to be minimized - can be
      - the number of additional workers needed to make the schedule
      feasible, or (once there is a feasible schedule)
      - the maximum percentage of Task X any worker has to do.

Thank you in advance!
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