2023 Quarterly Report 3

This quarterly report brings you reports on the ACP summer school, the CP conference, the CP awards, the CP competition results and the CP general assembly.

ACP.1: ACP Summer School 2023 in Leuven

From Monday July 10th to Friday July 14th the ACP summer school 2023 "Machine Learning for Constraint programming" (ML4CP). took place in Leuven, Belgium. The event, led by the team of prof. Tias Guns, brought together more than 90 participants - researchers, students, practitioners and experts - to explore the diverse applications and advancements emerging from the integration of Machine Learning with Constraint Programming. https://school.a4cp.org/summer2023/

All talks are recorded and the video's are available in a playlist on the ACP YouTube channel: https://www.youtube.com/playlist?list=PLcByDTr7vRTYJ2s6DL-3bzjGwtQif33y3

The lectures covered a diverse range of topics, Tias Guns was joined by nine well-established speakers: Quentin Cappart (Polytechnique Montreal), Ferdinando Fioretto (University of Virginia), Elias Khalil (University of Toronto), Wouter Kool (ORTEC), Lars Kotthoff (University of Wyoming), Michele Lombardi (Università di Bologna), Yingqian Zhang (TU Eindhoven), Hendrik Blockeel (KU Leuven) and Dimos Tsouros (KU Leuven). Slides and recordings are available on the website.

Complementing the insightful talks, the summer school featured interactive lab sessions, offering participants a hands-on perspective on covered topics. Attendees also took the opportunity to discuss their own work in the poster session where over 40 posters were presented. During the hackathon, participants creatively explored open questions from topics presented during the summer school, collaborating in groups of 3-5 people and comparing different approaches.

Of course, there was also an opportunity to connect in an informal setting during any of many social activities. Those who wanted culture joined the guided tour of Leuven, sporty participants proved their mettle in several ball games at a sports facility, and the relaxed gathered for a walking dinner. Naturally, those with a fondness of beer explored the many different flavors Leuven has to offer.

The organizers are happy with another successful edition of the ACP summer school, for the first time in Leuven. and want to thank anyone who contributed to this success, including the ACP, KU Leuven Arenberg Doctoral School, BNVKI an AI Journal who sponsored.

ACP.2: CP 2023 in Toronto

CP is the premier international event for presenting research in all aspects of computing with constraints, including, but not restricted to: theory, algorithms, environments, languages, models, systems, and applications. CP 2023 was held in-person in Toronto at the University of Toronto St. George campus (Downtown), August 27-31, 2023.

The CP 2023 program included presentations of high-quality scientific papers on constraints technology. In addition to the main conference program, CP 2023 featured 4 specialised tracks covering important topics in Constraints:

  • Applications
  • CP and Machine Learning
  • CP and Operations Research
  • Trustworthy Decision-Making

Please refer to the website for the full program: https://www.easychair.org/smart-program/CP2023/

On the first day of the conference (Sunday August 27th, 2023), there was a day of workshops and the CP Doctoral Program.

On the following days of the conference, apart from the technical paper presentations. We had tutorials and invited talks:


  • Explainable Constraint Solving - A Hands-On Tutoria by Ignace Bleukx, Dimos Tsouros and Tias Guns.
  • Machine Learning for Solvers by Vijay Ganesh

Invited Talks

  • Maria Garcia de la Banda (Monash University) Beyond optimal solutions for real-world problems
  • Jimmy Lee (Chinese University of Hong Kong) A Tale of Two Cities: Teaching CP with Story-Telling
  • Laurent Perron (Google, France) The CP-SAT-LP solver
  • Thomas Schiex (Universite Fédérale de Toulouse, ANITI, INRAE) Coupling CP with Deep Learning for Molecular Design and SARS-CoV2 variants exploration
  • Petr Vilím (ScheduleOpt) CP Solver Design for Maximum CPU Utilization

CP 2023 appreciates the generous support of our sponsors.

Gold tier sponsors:

Silver tier sponsors:

Organizing Committee

Conference Chair - Andre Augusto Cire (University of Toronto)

Program Chair - Roland Yap (National University of Singapore)

Local Chair - Eldan Cohen (University of Toronto)

Workshop Chair - Lars Kotthoff (University of Wyoming)

Tutorials Chair - Emir Demirović (TU Delft)

Doctoral Program Chair - Xavier Gillard (Université catholique de Louvain)

Publicity & Website Chair - Anna Latour (National University of Singapore)

DEI Chairs - Maria Andreina Francisco Rodriguez (Uppsala University)
- Andrea Rendl (Satalia)

Sponsorship Chair - Arvind Raghunathan (Mitsubishi Electric Research Laboratories)

Special Track Chairs - CP Applications Track: Helmut Simonis (Insight SFI Research Centre for Data Analytics)
- CP & Machine Learning Track: Tias Guns (KU Leuven)
- CP & Operations Research Track: Gilles Pesant (Polytechnique Montréal)
- CP & Trustworthy Decision Making Track: Peter Stuckey (Monash University)

Senior Program Committee and Program Committee

ACP.3: ACP Awards

ACP Doctoral Research Award

Honorable Mention to Gustav Bjordal for his PhD thesis on "From Declarative Models to Local Search".

And the award went to Stephan Gocht for his PhD thesis on "Certifying Correctness for Combinatorial Algorithms: by Using Pseudo-Boolean Reasoning"

ACP Early Career Researcher Award

Ciaran McCreesh receives the ACP Early Career Award for ongoing contributions to subgraph isomorphism algorithms, always with a strong CP angle to it, and the development of the Glasgow Subgraph Solver; as well as his recent developments in proof logging systems, and the new proof logging Glasgow Constraint Solver.

ACP Research Excellence Award

Awarded to Mats Carlsson for his fundamental contribution to CP, in advancing the state of the art in both theory and implementation. Mats is the main author of SICStus Prolog and its foundational clp(FD) constraint solver. He has developed optimization algorithms for a broad scope of topics, including industrial scheduling, sports scheduling, configuration, DNA sequencing, and frequency allocation.

ACP.4: ACP General Assembly

The slides of the general assembly can be found here: https://www.a4cp.org/sites/default/files/attachments/static-pages/72/agm2023.pdf

At the general assembly, ACP president David Bergman presented, among others: * The Executive Committee members and what the EC does * Announcements on the organisation of CPAIOR2024, CP2024, CP2025 and even CP2026 * CPAIOR 2024: 28-31 May 2024, in Uppsala, Sweden by Maria Andreina Fancisco Rodriguez, Justin Pearson and Pierre Flener * CP 2024: 2-6 September 2024, in Girona, Catalonia (Spain) by Miquel Bofil and Mateu Villaret * CP 2025 will be in Glasgow, Scotland (UK) and organized by Ciaran McCrees and Blair Archibald * CP 2026 even has some information we can share: it will be part of FLOC2026 in Lisbon, Portugal * The ACP award * EC initiatives, like stronger digital content (youtube channel), a 'teaching constraint programming' comprehensive repository and the CP+1 challenge * An update on DEI positions and efforts

The assembly ended with an open discussion on future conferences and AI 'fast tracks', the constraints journal and other topics on growing the community and strengthening relations within the AI and OR world.

CP competition reports

The CP conference ran two competitions:

The MiniZinc 2023 Challenge

The aim of the challenge is to compare various constraint solving technology on the same problems sets. The focus is on finite domain propagation solvers. An auxiliary aim is to build up a library of interesting problem models, which can be used to compare solvers and solving technologies.


And the results, with 3 gold medals for OR-Tools, one gold medal for Yuck, 2 silver medals for PicatSAT, one silver medal for SICStus Prolog, 2 bronze medals for Choco 4 and one bronze medal for iZplus: https://www.minizinc.org/challenge2023/results2023.html

The XCSP 2023 Competition

As usual for XCSP 3 competitions, the problem specifications were limited to the kernel of XCSP3, called XCSP 3-core, meaning integer variables, CSP and COPs and a set of 24 popular global constraints. 36 problems were selected and almost all problems are new in 2023, with models directly written in PyCSP3.


In the results across the 4 main tracks, Choco was twice ranked 1st, once 2nd and once 3rd; Picat was ranked 1st once, Mistral was once ranked 1st and once 2nd, toulbar2 and Fun-sCOP (kissat) were ranked 2nd once and CoSoCo was ranked 3rd two times.