ITC 2019: Two small corrections in the problem instances

[Tomáš Müller]

Dear competitors,

The following two issues have been discovered with the input data:

1) duplicate available times (both test and early data sets)

There are a few cases when a class has the same time listed two times. This was caused by the data entry in UniTime as it allows for multiple time patterns to be associated with the same class, and it is possible (though quite rare) for these time patterns to have overlapping times.

In most cases, both times have been with the same penalty. This is the case for iku-fal17, agh-,fis-spr17, pu-llr-spr07, and pu-c8-spr07.

There have been a few cases in two instances (bet-fal17 and pu-llr-spr17) where the same time for a class was listed two times with different penalization. In this case, the validator always picks the time with the smaller penalty (the time with the higher penalization is redundant).

Here is an example (from pu-llr-spr17):

<course id="618">

  <config id="635">

    <subpart id="706">

      <class id="895" limit="60">

        <time days="0101000" start="90" length="15" weeks="1111111111111110" penalty="44"/>

        <time days="0101000" start="90" length="15" weeks="1111111111111110" penalty="36"/>

        ...

      </class>

    </subpart>

  </config>

</course>

2) negative class length (test data sets)

The problem occurs only in the two test instances: class 448 in pu-llr-spr07 and class 1338 in pu-c8-spr07.

<course id="591">

  <config id="591">

    <subpart id="725">

      <class id="1338" limit="0">

        <room id="6" penalty="0"/>

        <time days="1000000" start="228" length="-2" weeks="100000000000000" penalty="0"/>

      </class>

    </subpart>

  </config>

</course>

These two instances are based on old data that we have published earlier (the original data are available at https://www.unitime.cz/uct_datasets.php used in the Complex university course timetabling paper). Unfortunately, in the original data, there was a class with zero length and as the travel time used to be computed differently, the conversion assumed that there are 10 minutes (2 slots) at the end of each class to travel from one class to the next. Hence the negative length of -2 (zero length minus the two slots allocated for travel to the consecutive class).

Also, as this class is fixed in both time and room, meets only once (on Monday at 7 pm during the first week), has no students associated with it, and it is not used in any distribution constraint, it either was a user error to begin with, or it was just created to show in the class schedule with no actual timetabling involved.

Both issues have been corrected in the problem instances and you can download the corrected instances from the competition website. The duplicate times, as well as the class with the negative length, have been removed. The changes have no effect on the consistency or quality of the solutions that have been already uploaded on the competition website or that has been successfully validated by the ITC 2019 validator. In the case of the duplicate times, the validator was already picking the time with the lower penalty. In the case of the class with the negative length, its placement incurred no penalization as the course had no students associated with it, the class had only one valid placement with zero penalization and it was not included in any distribution constraint.

Best regards,

ITC 2019 Organizers

organ...@itc2019.org