The shared engines under Raphaël Anjou's experiments. The named experiments are studies that run on these; this is the apparatus they share. The CSP presets and the Verhaard reimplementation are documented here; the constructive engines are not yet published.
The experiments are studies: each one asks a question and reports the board it reached. But most of them are not built from nothing. They run on a small set of shared engines, and the same engine turns up under experiment after experiment. This page documents that apparatus once, so the studies can point here instead of re-explaining the machine each time.
A single constraint-propagation engine with interchangeable orderings and propagators: arc-consistency, colour-graph matching, several fill orders. Faithful reimplementations of known community techniques, run under a dozen presets on the ten variants so the exact cost of each knob is on the leaderboard rather than argued about.
A from-scratch reimplementation of Louis Verhaard's eii method, since his own binary ships no source and will not run here. Set-composition swap-annealing under the 2×2-tiling metric; on the real five-clue puzzle it reaches 438 of 480, single core.
The two constructive engines these studies also lean on, the beam producer and the ALNS polish stage, do not yet have their own write-ups here; those pages are held back for now, and neither is on the benchmark leaderboard. Where an experiment steers one of them, its own page says what that engine does at the level the study needs, so nothing below depends on reading a page that is not here yet. The two engines documented and measured in full are the CSP presets and the Verhaard reimplementation.
A study and its engine answer different questions. The engine answers how the search works, the data structures, the fill order, the propagators, and it is reused unchanged across many studies. The study answers what happens when you point that engine at a particular idea: a learned prior, a fixed border, a break mask. Keeping them apart means a reader who wants to understand PRIOR's prior does not have to re-read how a beam works, and a reader who wants the engine gets it in one place, current and complete.
Where these engines race head to head under a fixed budget, they appear on the single-core benchmark. The general theory behind each method lives in the build-a-solver section; these pages are the specific engines as built and measured here.