ITC 2019: A small correction in pu-proj-fal19 instance

[Tomáš Müller]

Dear competitors,

There has been a small issue discovered with the pu-proj-fal19 instance: there are 16 required distribution constraints (all are either SameAttendees or NotOverlap), where the same class is listed two times. For example, there is class 1689 listed two times in the following NotOverlap constraint:

<distribution type="NotOverlap" required="true">
  <class id="1583"/>
  <class id="1599"/>
  <class id="1602"/>
  <class id="1689"/>
  <class id="1689"/>
</distribution>

The problem was caused by an instructor having the same class assigned two times (with a different role) in the original problem. Unfortunately, this problem has not been discovered earlier as the competition validator (as well as the UniTime solver) ignores such duplicates as a class cannot conflict with itself in a distribution constraint.

The pu-proj-fal19 instance is the only instance with such a problem, including the late instances that have not been published yet.

As this case may present an ambiguity for some solvers, the pu-proj-fal19 instance has just been corrected on the competition website. That is, the duplicate classes have been removed from these distributions.

If your solver is already ignoring the duplicate listings, no action is necessary. If it may have an issue with the same class being listed two times in a required SameAttendees or NotOverlap distribution constraint, please download the corrected pu-proj-fal19 instance from the competition website.

Best regards

Tomas Muller

organ...@itc2019.org