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Add experimental A* and CABS search - #256

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@zayenz zayenz commented Oct 13, 2026 •
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Add experimental A* and complete anytime beam search (CABS) for ordinary Gecode Space subclasses.

Guidance (an optimistic objective bound, an optional rank, and optional CABS dominance) is passed through Search::Options::guidance, so AStar<T>(s,o) and CABS<T>(s,o) have the same shape as BAB<T> and run directly with Script::run. The driver forwards Options::guidance(). CABS limits are Search::Options::max_width and frontier_limit. As with BAB, next() returns improving solutions.

Both engines support parallel search (Options::threads), dynamic worker control, and PBS portfolios with BAB. Open nodes, layers and beams use Gecode's Support containers; the shared pieces (node order, incumbent, A* queue, CABS beam) are in gecode/search/heuristic.hh, and parallel A* and CABS are small subclasses of Par::Frontier.

Commits:

  1. An option for experimental preview APIs (CMake, Autoconf, CI).
  2. Experimental changelog grouping.
  3. The A* and CABS engines, driver integration, and tests.
  4. Portfolio fix: a CABS asset that stops at its width or node limit no longer stops sequential or parallel portfolios. Search::Engine::limited() (experimental) reports such local limits; portfolios retire the asset and report an incomplete search once all assets are done. Other assets are handled as before. Sequential PBS also no longer takes a stop after a finished slice for the end of the slice.
  5. fifteen-puzzle gains -search astar|cabs; tsptw is a new driver-based example with two inline instances and a CABS dominance check.

Makefile.dep is regenerated in the stacked #269.

Enable with GECODE_ENABLE_EXPERIMENTAL=ON or --enable-experimental; the preview is disabled by default and its APIs may change.

Review: independent zdev reviews by two models; both found the parallel-portfolio issue fixed in commit 4, and two focused rechecks verified the fix.

Testing:

  • macOS arm64, CMake Release: -tag standard 6776/6777 passed; FlatZinc::on_restart::last_val_float also fails on main and is handled in feature/6.5.0-cleanups.
  • macOS, ASan+UBSan Debug: heuristic, worker-control and portfolio tests 283/283 over 10 iterations, no sanitizer reports; -tag check 536/536 with one test thread on the previous revision.
  • Experimental OFF: -tag check 533/533.
  • Linux (GCC 15, RelWithDebInfo): -tag check 539/539, no new warnings. Valgrind on the heuristic, worker-control and portfolio tests (previous revision): 14/14; the only report is the known 78-byte leak from static test registration.

🤖 Generated with Claude Code

@zayenz zayenz changed the title Add experimental heuristic search for Gecode 6.5 [Experimental work in progress] Add experimental heuristic search for Gecode 6.5 Oct 13, 2026
@zayenz
zayenz force-pushed the feature/open-search branch 5 times, most recently from 10fad23 to 4b24088 Compare October 14, 2026 12:11
@zayenz
zayenz force-pushed the feature/open-search branch from 4b24088 to 489e4c2 Compare October 15, 2026 12:49
@zayenz
zayenz force-pushed the feature/open-search branch 5 times, most recently from b599534 to bfe3f2f Compare October 15, 2026 15:10
@zayenz zayenz changed the title [Experimental work in progress] Add experimental heuristic search for Gecode 6.5 Add experimental A* and CABS search for Gecode 6.5 Oct 18, 2026
@zayenz zayenz mentioned this pull request Oct 18, 2026
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zayenz marked this pull request as ready for review October 20, 2026 06:50
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zayenz force-pushed the feature/open-search branch 2 times, most recently from 5c37b18 to 2e3068c Compare October 20, 2026 20:33
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zayenz force-pushed the feature/open-cp branch 2 times, most recently from 0e679a7 to 5fb98a6 Compare October 21, 2026 08:11
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zayenz force-pushed the feature/open-search branch 4 times, most recently from a03e61d to ace7c7f Compare October 21, 2026 12:02
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zayenz force-pushed the feature/open-search branch 2 times, most recently from 7c04635 to 8d491da Compare October 21, 2026 19:25
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zayenz force-pushed the feature/open-search branch from fe151fe to 5c83ea5 Compare October 21, 2026 20:44
@zayenz zayenz changed the title Add experimental A* and CABS search for Gecode 6.5 Add experimental A* and CABS search Oct 21, 2026
@zayenz
zayenz force-pushed the feature/open-search branch 2 times, most recently from 9690a92 to e3cdb68 Compare October 22, 2026 14:05
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zayenz force-pushed the feature/open-search branch from e3cdb68 to 3c4cc55 Compare October 22, 2026 17:18
@zayenz
zayenz force-pushed the feature/open-search branch 5 times, most recently from bbf762e to 11e7c25 Compare October 26, 2026 18:40
Base automatically changed from feature/open-cp to main October 27, 2026 11:46
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zayenz force-pushed the feature/open-search branch 3 times, most recently from 0bc31b6 to b31ea94 Compare October 28, 2026 05:57
@zayenz zayenz mentioned this pull request Oct 28, 2026
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zayenz and others added 5 commits October 28, 2026 09:57
@zayenz @claude
Add an option for experimental preview APIs
4875544 
GECODE_ENABLE_EXPERIMENTAL (CMake) and --enable-experimental
(Autoconf) define GECODE_HAS_EXPERIMENTAL. The option is off by
default; CI builds both settings.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
@zayenz @claude
Group experimental changelog entries
1c69ad7 
Entries marked Experimental: true appear under Experimental changes in
each release, and tidy validates the field.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
@zayenz @claude
Add experimental A* and CABS search
32a5a31 
AStar and CABS (complete anytime beam search) are best-solution
engines for ordinary Space subclasses. Their guidance, an optimistic
objective bound with an optional rank and optional CABS dominance, is
passed through Search::Options::guidance, so they have the same
constructor as BAB and run with Script::run; the driver forwards
Options::guidance. Search::Options::max_width and frontier_limit bound
CABS.

Both engines support parallel search, worker control, and portfolios.
Open nodes, layers and beams use the Support containers; node order,
incumbent, A* queue and CABS beam are shared in search/heuristic.hh,
and parallel A* and CABS are subclasses of Par::Frontier.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
@zayenz @claude
Keep portfolios running when an asset stops at a local limit
dacf16b 
A CABS asset that reaches its width or node limit cannot continue, but
both portfolio engines took its stop for a user stop: the sequential
one kept returning without running the other assets, and the parallel
one stopped the portfolio while keeping the asset. Search::Engine::limited
now tells that an engine stopped at a local limit; portfolios remove such
an asset and report that they stopped once all assets are done. Other
assets are handled as before. The sequential engine also no longer takes
a stop after a finished slice for the end of the slice.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
@zayenz @claude
Add A* and CABS to the fifteen-puzzle and add a TSPTW example
52ad2b6 
The fifteen-puzzle gains -search astar|cabs using the moves so far plus
the Manhattan distance as bound. TSPTW is a driver-based travelling
salesperson model with time windows and two inline instances; it runs
with BAB, A* and CABS, and CABS uses a dominance check on partial
tours.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
@zayenz
zayenz force-pushed the feature/open-search branch from b31ea94 to 52ad2b6 Compare October 28, 2026 10:33

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