Weird instructor scheduling

[matoats]

Hello, Unitime Team!

We've encountered with some strange Instructor scheduler behavior.

There's one Instructional Offering in test mode. It consists of 6 subparts 1x45 taught all in one day, none of them are grouped or in a parent-child relationship.

Each subpart has a teaching request with required instructor attributes: Attr-A and Attr-B. There are no instructors assigned manually. No particular instructor preference is used. Same Course Preference is set to Neutral.

There are 2 equal instructors on the instructor list with both attributes (A and B) set on, each instructor has Preferred scheduling preference except the following: Instructor 1 is available all days and all times a week, Instructor 2 availability is PROHIBITED from 11am till the end of day. Both instructors have a greater teaching load than in subparts' teaching requests.

We start Instructor Scheduler after the Timetable Solver is done. Strange but it assignes Instructor 2 (who is set to prohibited from 11am - ) to all classes independent of his unavailability, neither it offers sharing the teaching load between two instructors. After committing the Instructor solution, all classes he was assigned to just disappear from the timetable grid.

Clearing class assignments, reloading input data, deleteng timetables and running slovers again don't help.
The solver uses Instructor 1 only if Instructor 2 teaching preference is set to 'prohibited'. If both are 'preferred' or 'neutral', mostly unavailable instructor 2 keeps to be assigned to classes at slots that are prohibited.

How do we adjust proper Instructor scheduling balance and set up the Solver not to use prohibited instructor time slots?

Thank you!

[tomas-muller]

First of all, based on the screenshot, there is no course timetable (assigned classes show no time assignments)-- if you need class times to be considered, you need to have a course timetabling done first. The instructor scheduling solver needs to be loaded and run after the course timetabling solution has been saved and committed.

Also, by default, the instructor scheduling solver tries to minimise the number of instructors used by heavily penalising any unused teaching load held by the instructors who are being used. This is why it will try to use just one instructor rather than spreading the load between two.

To avoid that (i.e., disable the UnusedInstructorLoad criterion), you will need to create a solver parameter Weight.UnusedInstructorLoad (using Administration > Solver > Parameters page and the following settings) and set it to zero.

Once created, you can change the value of this parameter for your solver configuration using Administration > Solver > Configurations page, e.g., if you want to experiment with different settings. E.g., you can try to set it to a negative value to encourage the solver to create unused instructor load rather than trying to avoid it.

[matoats]

It seems strange for me either, but the course timetable exists. Even if i clear all hard constraints and the solver assigns instructors to all classes without conflicts, the Instructor solution is committed and those instructors appear in the timetable grid, the Teaching Assignments screet always shows No dates, No hours, No rooms...

Thank you for the solver parameter, I'll try it now!

But the question is still bugging me - among two instructors the solver choses the most unsuitable one - with severe prohibited time slots. Even if I set the Teaching Preference of that instrcutor to "Strongly discouraged" combined with most time slots "Prohibited", the Solver picks this instructor anyway independent of the other fully available instructor. Aren't "Prohibited" and "Strongly discouraged" considered hard constraints?

Thank you!

[tomas-muller]

Required and prohibited are hard constraints; others are soft.

But prohibiting certain times when their class has no time assigned does not make a difference.

Check the Courses > Course Timetabling > Saved Timetables page. For each defined course timetabling problem (solver group), there should be a line in the Saved Timetables table that also indicates that the solution has been Committed.

[matoats]

Setting Weight.UnusedInstructorLoad parameter to -500 worked like magic and did its job!

So saving a Course Timetable isn't enough? It has to be committed and appear in Events Timetable. I always ran the Instructor Scheduler when there was a saved timetable and thought the sequence had to be as follows:

1. Solve Course timetable
2. Save course timetable without committing
3. Solve instructors and commit
4. Commit the Course Timetable with already pre-assigned instructors.

Anyways, starting the Instructor Scheduler on a committed Course timetable now considers all constraints.

Thank you very much!

[tomas-muller]

Indeed, saving a course timetable without committing is not enough -- there could be multiple solutions saved for each solver group. Committing a solution would make it available to other modules and to anyone outside of the department. This is also important when multiple problems/solver groups share some instructors, students, and/or rooms. Running a solver for one problem will consider all other problems that are already committed.

The instructor scheduling solver was originally designed to work for Teaching Assistant assignments, so it can be run way later in the process. It will, for instance, check the availability of instructors based on the classes they are taking as students (both student and instructor records must have the same external id for that), making sure that a TA does not get to teach a class at the same time they are attending some other class as a student.