Circuit constraint respecting the order of the next n jobs / jobs on each machine starting at 0

Question

I am working on a scheduling problem in OR-Tools using the CP-SAT solver.

I'm working with python but I managed to rebuild this solution as starting point: Optimal way to ensure optional intervals are consecutive in OR-Tools

Just like in that problem I also have the constraint, that the jobs are consecutive. This works already.

My first problem is really easy in my mind, but somehow I cant make it work: the first job on each machine MUST start at 0.

Second problem: lets say I produce n colors of the same product. Every one of these $n$ colors has a maximum $i$, which is the maximum number of jobs of the same color I can build in sequence on the same machine.

My solution pretty much depends on my x[job,machine] dict where x[job,machine] is true if job is performed on machine.

Answer 1

for 1) Look at this literal in the jobshop with setup times. You just need to add:

model.Add(start_of_job == 0).OnlyEnforceIf(start_lit)

For 2) For each color, add for each job a variable ranging from 0 to max_sequence_length for this color.

For each arc, you know if job_i has the same color as job_j. If true, the

model.Add(sequence_length[color][j] = sequence_length[color][i] + 1).OnlyEnforceIf(lit)

else

model.Add(sequence_length[color_i][j] == 0).OnlyEnforceIf(lit)
model.Add(sequence_length[color_j][j] == 1).OnlyEnforceIf(lit)

And do not forget to initialize all sequence lengths vars with the start_lit literal.