teacher work half day (one from two specific days)

[dimzev]

I have the following problem.
A teacher cannot work the first 4 hours of Tuesday or Thursday.
do i have to make two different programs and try?
or there is an easier way.
Because if I have two such teachers I will have to make 4 different programs etc ...

[Volker Dirr]

Depending on if gaps are critical or not.
If not:
You can add an activitiy with duration 4. Add the teacher, but no students and add a constraint preferred starting time on Tuesday and Thurstday.

[dimzev]

I did not understand...
but maybe I was not clear.
I clarify ..
the teacher can work Tuesday any from 5 or 6 or 7 hours and any hour from Thursday
or
any hour from Tuesday and from Thursday only from any 5 or 6 or 7 hour
the teacher have 23h/w with different groups and subgroups
how can give above to FET?
.

[Volker Dirr]

and use the trick i wrote above:
add an activity with duration 4. use a constraint to allow that activity to start only Thurstday or Tuesday the first hour. Add the teacher, but don't add students. Maybe call the subject "not available".

[dimzev]

ooooo!!!
Thank you !!!!
I don't know this trick ...

[Volker Dirr]

We call that "pseudo activity". A problem might be the gaps, since FET will count gaps between that pseudo activity and the following "real" activitiy. So if you use max gap constraint for that teacher and your timetable is too difficult we must think about a better variant.

[fourat]

regarding the gaps I have a trick : add an imaginary teacher  Tx working with the real teacher T in real activities.
The pseudo-activities that Volker cited will be assigned only to the imaginary teacher tx
Max gaps and similar constraints will only affected the real teacher

[Volker Dirr]

Very nice trick!