Different arrival times [feature request]

[Maros112358]

Hello, I would like to solve a JSSP problem with different arrival times. Some of the jobs should be available at start t = 0, and others should arrive at time t > 0. I tried to use Wheatley for this purpose, but as far as I know, it does not support this feature right now. Would it be possible to add this feature to Wheatley?

[fantes]

Hi @Maros112358
we do not have such thing natively, for now our plan to deal with such case is to add "virtual" tasks that do not use any resource but have to be done before the job (or the first task of job) starting at time t > 0.

[Maros112358]

Hello @fantes, thank you for the quick reply. Your idea sounds like what I want. Are you planning to implement this in the near future? Or can this be done with Wheatley right now?

[fantes]

Using the rcpsp code, this should work directly by adding such jobs in the problem description file.
In jssp this is a bit more complicated, as tasks have to use a resource so this implies also adding extra "virtual" resources, one per such virtual task in order to be sure that they do not interfere. (a -1 in the description file means that the tasks should not be scheduled at all, not that it does not use any resource). Hope this helps

[Maros112358]

Hello @fantes, I tried implementing the proposed solution, and I would like to just make a quick check with an example if I understood you correctly.

This is 6x6 JSSP instance in Taillard specification

6	6
1	3	6	7	3	6
8	5	10	10	10	4
5	4	8	9	1	7
5	5	5	3	8	9
9	3	5	4	3	1
3	3	9	10	4	1
3	1	2	4	6	5
2	3	5	6	1	4
3	4	6	1	2	5
2	1	3	4	5	6
3	2	5	6	1	4
2	4	6	1	5	3

For each job, I generated arrival times [7, 0, 0, 5, 8, 0] (first job starts at time 7, second at 0, ...). The JSSP instance in Taillard specification with virtual tasks should then look like this:

6	6
7      1	3	6	7	3	6
8	5	10	10	10	4
5	4	8	9	1	7
5	5	5	5	3	8	9
8	9	3	5	4	3	1
3	3	9	10	4	1
7	3	1	2	4	6	5
2	3	5	6	1	4
3	4	6	1	2	5
8	2	1	3	4	5	6
9	3	2	5	6	1	4
2	4	6	1	5	3

If it's correct, I can prepare a pull request with the code snippet I used.

[fantes]

Hello @Maros112358
I think the reader/parser will not be able to read files with holes. I would try to also add tasks with a duration of zero (at beginning of jobs 2,3 and 6) and specify that the jssp problem is of size 7 x 6 (or 6x7, I cannot remember which one is number of tasks/number of jobs). Wheatley should be able to deal with null durations directly. I am less sure for ortools/cp-sat, you will have to test. Hope this helps.

[Maros112358]

Hello @fantes,
it worked correctly even with holes. Wheatley filled the rest automatically.

[fantes]

ok, that is pretty cool. Just keep in mind that we did not test this case, so do not hesitate to double/triple check the results.