Difficult situation, for me

[Andrés Chandía]

Hi guys, I have the next situation:
A group of activities, 10 divided in two groups A (5) and B (5), between all of the 10, until 3 can be overlapped (A1-A2-A3 or A1-B1-B5 or any combination), but not a fix group of them, i mean whichever 3 randomly, if and only if by coincidence both groups A and B are assigned to the same day, because there's another restriction that says that all of the A activities have to be the same day, same for B.
Again, if it happens that A and B are the same day (summing 10 activities) only 3 of them can be overlapped, but if possible I wouldn't want to define which 3 can not be overlapped, because this should be randomly.
I hope it is not too complicated for understanding it, or that I was not clear in my explanation.
Well, the thing is that I don't know how to express this in FET. :-/
Tnx.

[Andrés Chandía]

Sorry, some more specifications:
Also if only one of the groups happens one day, I mean 5 activities only, also I would need until 3 overlapped, and also in a random combination.

Tnx again.

[Liviu Lalescu]

Do you mean you have activities A1..A10 and maximum 3 should be in the same day? Maybe you could use constraint teachers or students activity tag max 3 hours daily, if you add the same activity tag to all 10 activities. Maybe you need to add a dummy teacher or students set to all these activities, so that they share a teacher or a students set and you can use this constraint for the dummy teacher or students set.

[Andrés Chandía]

Not exactly what you say, but anyway I think your proposal would be a solution:
The situation is:
Activities
A1, A2, A3, A4, A5, B1, B2, B3, B4, B5.
Always A1.... are the same day
Always B1.... are the same day
Could be that A1.... and B1.... are the same day
In all the 3 cases, if there are 5 or 10 activities the same day, only 3 of them (randomly) can be overlapped.

[Volker Dirr]

i think that is maybe very easy if you didn't add room constraints yet.
just add a constraint that this activities have preferd rooms (3 rooms).
so never more then 3 activities can overlap.

if you already have (other) room constraints to that activities, then you need to set pseudo activities to each activitiy. the pseudoactivities must be conected with a sme starting time constraint to an activity. then do the room hint to the pseudo activities.

the other problem is esay to solve. just add a time constraint same day to the A activities. similar to the B activities.

yes, much to enter, but i don't know a faster variant at the moment.

[Andrés Chandía]

I have added rooms constraint already, but I solve it following Liviu's suggestion.
As I got a subject divided in two: Subject1.1 - Subject1.2, both making two different activities, and each activity divided into five different subactivities, at the previous example A1, A2..... , B1, B2......
To all of the 10 subactivities I added the tag Subject1, then on the time constraints I used the one that says that a group of activities do not overlap, defining the group by the tag, and giving it a low average 30%, or 40%, to allow them to overlap at least three, but no more than that.
I hope this help if somebody else finds this same situation.