I need at least 1 teacher free each period

[juancmar]

I need at least 1 teacher free each period of the week, how can I do it?

I tried to do it making one group and a subject, and making the activity for that subject with all the teachers, but FET thinks that ALL of the teachers must be there, and I need ANY of the teachers to be. I cannot find the solution. Any suggestion?

[Volker Dirr]

use dummy activities.

so add activities with one teacher, a subject (maybe -) and no students set. maybe also use an activity tag "free" for this activities, so you can add some constraints to that activty tag (because you maybe don't want that is dummy activity is scheduled in the first or last period.)

maybe also read this:
http://www.timetabling.de/manual/FET-manual.en.html#id_22

[Liviu Lalescu]

Volker's approach might be good, but I must give some more details:

Here is one possible solution: if you know for instance that teacher T1 must have 3 free periods per week, T2 -> 2, T3-> 4, and so on, then: add activity A (T1, Subject: Free, no students), split into A1, A2, A3, then A' split into A4 and A5 (T2), then A6, A7, A8 and A9 (T3). Each has duration 1 hour. Then, a crucial step: add constraint activities not overlapping: A1, A2, ..., A9, ....

If you don't know which teacher has how many free hours to supervise the school, then I don't see for now a solution. Maybe you can try an approximate approach using the above method.

Later edit: you have activities A1...AN, where N is the number of periods per week: days*hours. In the constraint activities not overlapping, you add all these N activities.

[Volker Dirr]

Instead of using not overlapping constraints you can also work with a dummy room.

just add constraint activity tag "free" need room "pseudo room". so that activites will never overlap.

[Liviu Lalescu]

Reviving an old topic: you can use the new constraint activities max simultaneous in selected time slots (select all time slots and all activities, max simultaneous = number of teachers - 1). This constraint was introduced in FET-5.15.0.

[Volker Dirr]

Yes, that new constraints help (a bit), because you still need to think about not available times and free days.
You can avoid that by dummy activities (for not available times and free days), but if you use dummy activities you have disadvantages with other constraints like min/max n days/hours and gaps constraints.