Perturbation penalty computation.
In practice, the strategy for computing perturbations needs to be extended.
For example, a change in time is usually much worse than a movement to a
different classroom. The number of enrolled/involved students should also be
taken into account. Another factor is whether the solution has already been
published or not.
The priorities for evaluating perturbations are as follows. Before publishing
timetable:
In both cases, the number of classes with room change is not significant at
all. Before the timetable is published, minimizing the number of classes with
time changes is the most important criteria for the MPP as long as it does
not create too many additional student conflicts in the process. Therefore,
as a compromise, the cost (in equivalent conflicts) of changing the time
assigned to a class equals a number like 5% of the students enrolled in that
class. Otherwise none of our other criteria would have any importance.
Similar properties apply between other criteria as well. To fulfill all these
needs we have created a function (called perturbations penalty) which can be
computed over a partial solution. This is a weighted sum of various
perturbations criteria like the number of classes with time changes or the
number of additional student conflicts. This perturbation penalty is added as
an extra optimization criterion to the solution comparator and to value
selection criterion, so we can also setup the weights between this
perturbation penalty and other (initial) soft constraints.
Related Solver Parameters
| Parameter |
Type |
Comment |
| Perturbations.DifferentPlacement |
Double |
Different value than initial is assigned |
| Perturbations.AffectedStudentWeight |
Double |
Number of students which are enrolled in a class which is placed to a
different location than initial (a student can be included twice or more) |
| Perturbations.AffectedInstructorWeight |
Double |
Number of instructors which are assigned to classes which are placed to
different locations than initial (an instructor can be included twice or
more) |
| Perturbations.DifferentRoomWeight |
Double |
Number of classes which are placed to a different room than initial |
| Perturbations.DifferentBuildingWeight |
Double |
Number of classes which are placed to a different building than initial |
| Perturbations.DifferentTimeWeight |
Double |
Number of classes which are placed in a different time than initial |
| Perturbations.DifferentDayWeight |
Double |
Number of classes which are placed in a different days than initial |
| Perturbations.DifferentHourWeight |
Double |
Number of classes which are placed in a different hours than initial |
| Perturbations.DeltaStudentConflictsWeight |
Double |
Difference of student conflicts of classes assigned to current placements
instead of initial placements. It is a difference between number of students
conflicts which are in the initial solution and the current one. Student
conflicts created by classes without initial placement are not taken into
account |
| Perturbations.NewStudentConflictsWeight |
Double |
New created student conflicts -- particular students are taken into
account. Student conflicts created by classes without initial placement are
not taken into account |
| Perturbations.TooFarForInstructorsWeight |
Double |
New placement of a class is too far from the intial placement
(instructor-wise). It is computed only when the class has an instructor
assigned, moreover:
- 0 < distance(currentPlacement,initialPlacement) <= 5 .. weight is taken
once
- 5 < distance(currentPlacement,initialPlacement) <= 20 .. weight is taken
twice
- 20 < distance(currentPlacement,initialPlacement) .. weight is taken ten
times
|
| Perturbations.TooFarForStudentsWeight |
Double |
New placement of a class is too far from the intial placement
(instructor-student). It is weighted by the number of students enrolled in
the class when distance(currentPlacement,initialPlacement) > 67 |
| Perturbations.DeltaInstructorDistancePreferenceWeight |
Double |
Difference between number of instructor distance preferences of the
initial (but maybe inconsistent) solution and the current solution.
Instructor distance preferences of classes without initial placement are not
taken into account |
| Perturbations.DeltaRoomPreferenceWeight |
Double |
Difference between room preferences of the initial and the current
solution. Room preferences of classes without initial placement are not taken
into account |
| Perturbations.DeltaTimePreferenceWeight |
Double |
Difference between time preferences of the initial and the current
solution. Time preferences of classes without initial placement are not taken
into account |
| Perturbations.AffectedStudentByTimeWeight |
Double |
Number of students which are enrolled in a class which is placed to a
different time than initial |
| Perturbations.AffectedInstructorByTimeWeight |
Double |
Number of instructors which are assigned to classes which are placed to
different time than initial |
| Perturbations.AffectedStudentByRoomWeight |
Double |
Number of students which are enrolled in a class which is placed to a
different room than initial |
| Perturbations.AffectedInstructorByRoomWeight |
Double |
Number of instructors which are assigned to classes which are placed to
different room than initial |
| Perturbations.AffectedStudentByBldgWeight |
Double |
Number of students which are enrolled in a class which is placed to a
different building than initial |
| Perturbations.AffectedInstructorByBldgWeight |
Double |
Number of instructors which are assigned to classes which are placed to
different building than initial |