Writing a custom propagator is worth considering when one constraint carries much of a problem's structure. My paper Propagation Algorithms for the Minimum-Distance Constraint over Selected Points, to be presented at ModRef 2026, works through one such case in Gecode.

Suppose we want to select five facility locations, spread out so that the closest pair is as far apart as possible. Let z denote that minimum distance. A straightforward CP model introduces a distance variable for every selected pair, then constrains z to be the minimum of those distances. This is a clear specification, but it creates quadratically many auxiliary variables and propagators.

There is now a public collection of 434,201 generated Sudoku instances, ranging from 6×6 to 36×36. The paper describes how the collection was generated, and its experiments provide a map for navigating it.

We needed to arrange the tables for a real wedding. That practical problem became the MiniZinc model in No More Awkward Silences with Table Talk Tuning, a paper by Martin Butler and me to be presented at ModRef 2026.

A seating plan can satisfy every capacity and grouping request and still leave someone with little to talk about. That gap was visible in the actual planning problem, so the model treats conversational fit as part of the assignment rather than something to inspect afterwards.

The paper The Work Task Variation Problem by Mikael Z. Lagerkvist and Magnus Rattfeldt was presented at the 31st International Conference on Principles and Practice of Constraint Programming (CP 2025) in Glasgow, Scotland. This post summarizes the paper and provides some context.

The paper is available on my research page and the benchmark instances and MiniZinc model are available on GitHub.

The paper Half-checking propagators by Mikael Z. Lagerkvist and Magnus Rattfeldt is presented at the 19th workshop on Constraint Modelling and Reformulation at The 26th International Conference on Principles and Practice of Constraint Programming, CP2020.

This post summarizes the paper and gives some context on it. The paper is available on my research page. You can also watch the presentation given at the workshop if you are interested.

This paper has now been published at ModRef 2020. Please see the updated post that includes a video presentation.

The paper Half-checking propagators by Mikael Z. Lagerkvist and Magnus Rattfeldt is now available from arXiv. This post summarizes the paper and gives some context on it. The paper is available on my research page.

Nmbr9 as a Constraint Programming Challenge, a paper by Mikael Z. Lagerkvist

State Representation and Polyomino Placement for the Game Patchwork, a paper by Mikael Z. Lagerkvist

Monte Carlo Methods for the Game Kingdomino, a paper by Magnus Gedda, Mikael Z. Lagerkvist and Martin Butler