Does order matter for split activities?

Started by robbo, June 10, 2023, 01:19:25 PM

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robbo

I have a lot of 6-lesson activities. I use sub-activities to change the teachers for some of them. Does the order matter? Some of the teachers are part-time and it isn't finding a solution.

Volker Dirr

#1
You mean you have an activity with total duration 6 and split it for example like this:
2-2-1-1
and the other time you split it like this:
1-1-2-2

In normal case the order doesn't matter.

Except if you use a constraint like "subactivities preffered starting time", since in constraints like that you choose the component number (split index). So if you choose split index 1 in such a constraint, then it will affect the first subactivity with duration 2 in the first example, but in the second example it will affect the subactivity with duration 1.

robbo

#2
Thank you for the reply. I split them like this, worst case:

1/6 Teacher A
2/6 Teacher A
3/6 Teacher B
4/6 Teacher B
5/6 Teacher C
6/6 Teacher C

Most blocks are split 3:3.

I use activity tags to group them and then constraints to say tags mustn't overlap.

So, if A works Th, Fr, Sa and B works M, Tu, W would I be better ordering the sub-activities to put C first and A last?

Volker Dirr

#3
ah. Ok. In fact it is nearly the the same answer (read carefully, i modified a bit):

In normal case the order doesn't matter.

Except if you use a constraint like "subactivities preffered starting time", since in constraints like that you choose the component number (split index). So if you choose split index 1 in such a constraint, then it will affect the first subactivity with teacher A in your example, but with an other order it will affect the subactivity with an other teacher (C).

robbo

Thanks. So, I am only using tags, say:

U6-A
U6-B
U6-C
U6-D
U6-X

Then one constraint that says they must not overlap.

Volker Dirr

#5
So if you swap a teacher, do you also swap the tag?
If you also swap the tag, then the order doesn't matter.

If you swap the teacher, but not the tag, then it might matter.
it is depeding on what constraints you use. Only not overlapping tags constraint? Then the order doesn't matter.
If you use different preffered time constraints with that tags, then it matters.
In fact in that case it is not the order that matters, the "correct" reason is that an other differnt tag is connected to an other teacher. So it matter in that case.

Volker Dirr

Please read my previous answer once again. I just modified it.

robbo

Hi

All six activities have the same tag. Is it okay if I email my input file, please? I can't see why it won't solve. :(

Volker Dirr

I haven't much time at the moment (i have much time in 2 weeks), but i can have a quick look now. So you can email me.

robbo

Thanks. Sorry for delay in replying. It turned out I wasn't allowing enough time for it to find a solution. 9-16hrs needed!

Liviu Lalescu

Wow! That is something (though not the record).

If you have more cores, you can generate multiple with nThreads=n_cores_you_have, and FET might find a solution faster.