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Release notes

Fast Downward has been in development since 2003, but the current timed release model was not adopted until 2019. This file documents the changes since the first timed release, Fast Downward 19.06.

For more details, check the repository history (https://github.com/aibasel/downward) and the issue tracker (https://issues.fast-downward.org). Repository branches are named after the corresponding tracker issues.

Changes since the last release

  • Add debugging methods to LP solver interface. https://issues.fast-downward.org/issue960 You can now assign names to LP variables and constraints for easier debugging. Since this incurs a slight runtime penalty, we recommend against using this feature when running experiments.

  • Support integer variables in linear programs. https://issues.fast-downward.org/issue891 You can now use the LP solver interface to solve mixed integer programs. In particular, the operator-counting heuristics now have an option use_integer_operator_counts that improves the heuristic value by forcing operator counts to take integer values. Solving a MIP is NP-hard and usually takes much longer than solving the corresponding LP.

  • For developers: move functionality used during search away from LandmarkGraph, making it constant after creation. https://issues.fast-downward.org/issue988 https://issues.fast-downward.org/issue1000

  • For developers: new state class https://issues.fast-downward.org/issue348 We unified the classes GlobalState and State into a new class also called State. This removed a lot of code duplication and hacks from the code. A description of the new class can be found in the wiki: https://www.fast-downward.org/ForDevelopers/Blog/A%20Deeper%20Look%20at%20States

  • For developers: introduce class for delete-relaxation based landmark factories and move usage of exploration object to subclasses of (abstract) landmark factory class. https://issues.fast-downward.org/issue990

  • For users: We removed options from LandmarkFactories that were not relevant, renamed the option "no_orders" to "use_orders" and changed the reasonable_orders option to a Factory. https://issues.fast-downward.org/issue995 Removed options: lm_exhaust: disjunctive_landmarks, conjunctive_landmarks, no_orders, reasonable_orders lm_hm: disjunctive_landmarks, only_causal_landmarks, no_orders, reasonable_orders lm_merged: disjunctive_landmarks, conjunctive_landmarks, only_causal_landmarks, no_orders, reasonable_orders lm_rhw: conjunctive_landmarks, no_orders, reasonable_orders lm_zg: disjunctive_landmarks, conjunctive_landmarks, only_causal_landmarks, no_orders, reasonable_orders Added options: lm_hm/lm_rhw/lm_zg: use_orders (negation of removed option "no_orders") New Factory "lm_reasonable_orders_hps": This factory approximates reasonable orders according to Hoffman, Porteus and Sebastia ("Ordered Landmarks in Planning", JAIR 2004) and is equivalent to the removed option "reasonable_orders", i.e. the command line argument --evaluator hlm=lmcount(lm_factory=lm_reasonable_orders_hps(lm_rhw())) is equivalent to the removed command line argument --evaluator hlm=lmcount(lm_factory=lm_rhw(reasonable_orders=true))

  • For developers: add support for Github actions https://issues.fast-downward.org/issue940

  • For developers: We cleaned up the code of LandmarkGraph. Some of the public methods were renamed. This class will undergo further changes in the future. https://issues.fast-downward.org/issue989

  • Debug builds with LP solvers vs. the _GLIBCXX_DEBUG flag https://issues.fast-downward.org/issue982 Previously, we used the flag _GLIBCXX_DEBUG in debug builds for additional checks. This makes the binary incompatible with external libraries such as LP solvers. The flag is now disabled by default. If no LP solvers are present or LP solvers are disabled, it can be enabled by setting the CMake option USE_GLIBCXX_DEBUG. The build configurations debugnolp and releasenolp have been removed, and the build configuration glibcxx_debug has been added.

  • For developers: decide on rules regarding software support and improve Github actions accordingly https://issues.fast-downward.org/issue1003

  • For developers: add CPLEX support to our GitHub Actions for Windows https://issues.fast-downward.org/issue1005

  • Fix a bug in the computation of RHW landmarks https://issues.fast-downward.org/issue1004

  • Only build configurations defined in build_configs.py are loaded in the build.py script. https://issues.fast-downward.org/issue1016

  • Replace size_t by int for abstract state hashes in PDB-related code https://issues.fast-downward.org/issue1018

  • Integrate the pattern generation methods based on CEGAR https://issues.fast-downward.org/issue1007

  • Integrate the random pattern generation methods https://issues.fast-downward.org/issue1007

  • For developers: change public interface of generation of random ints and doubles in the RandomNumberGenerator class https://issues.fast-downward.org/issue1026

  • For developers: we separate the functionality of landmarks from the functionality of landmark nodes by introducing a new Landmark class https://issues.fast-downward.org/issue999

  • For developers: use RandomNumberGenerator class in VariableOrderFinder https://issues.fast-downward.org/issue1032

  • For users: the driver now finds domain files -domain. for task files called . https://issues.fast-downward.org/issue1033

  • For users: the build system now prefers compilers cc/c++ found on the path over gcc/g++. As before, environment variables CC/CXX can be used to override this choice. https://issues.fast-downward.org/issue1031

  • For developers: Add option to use a local (configurable) logger instead of the global one. https://issues.fast-downward.org/issue964 Classes which want to configure the logger (currently only the verbosity level can be configured) should now use the facilities add_log_options_to_parser and get_log_from_options to obtain their local log object.

  • Fix a failing assertion in the landmark factory RHW triggered by unsolvable tasks. https://issues.fast-downward.org/issue467

  • Remove a failing assertion in the lm_zg landmark factory. The issue was triggered by an overly optimistic approximation of relaxed reachability in the presence of conditional effects. While the assertion failed, this did not affect soundness of the other places where the same function is used. Nevertheless, we changed the approximation to become stricter which can lead to lm_rhw, lm_zg, and lm_exhaust finding more landmarks and landmark orderings. https://issues.fast-downward.org/issue1041

  • Fix a bug where the Zhu/Givan landmark factory lead to a crash on relaxed unsolvable tasks due to returning an empty landmark graph. https://issues.fast-downward.org/issue998

  • Delete-relation constraints can now be used in the operator-counting framework. The constraints defined by Imai and Fukunaga (JAIR 2015) encode different relaxations of the delete-relaxation heuristic. For details, see our documentation. https://www.fast-downward.org/Doc/ConstraintGenerator#Delete_relaxation_constraints Additionally, we fixed a bug which induced inadmissible heuristic values when using CPLEX for optimal planning with large action costs and/or long plans (only operator-counting heuristics with integer variables and tasks with total costs starting from 10'000 were affected). https://issues.fast-downward.org/issue983

  • The landmark factories can handle cycles of natural orderings without crashing. Since the planning task is unsolvable in these cases, they signal this by clearing the first achievers of the involved landmarks. https://issues.fast-downward.org/issue937

  • New LimitedPruning class replaces previous limitation options of individual pruning methods http://issues.fast-downward.org/issue1042 A previous command line option using this feature, such as --search "astar(lmcut(),pruning=atom_centric_stubborn_sets(min_required_pruning_ratio=0.2,expansions_before_checking_pruning_ratio=1000))" is now changed to --search "astar(lmcut(),pruning=limited_pruning(pruning=atom_centric_stubborn_sets(),min_required_pruning_ratio=0.2,expansions_before_checking_pruning_ratio=1000))

  • All pattern (collection) generators now have an option "verbosity" to set the desired level of output. https://issues.fast-downward.org/issue1043 Internally, generators now use their own logger rather than g_log.

Fast Downward 20.06

Released on July 26, 2020.

Highlights:

  • The Singularity and Docker distributions of the planner now include LP support using the SoPlex solver out of the box. Thank you to ZIB for their solver and for giving permission to include it in the release.

  • The Vagrant distribution of the planner now includes LP support using the SoPlex and/or CPLEX solvers out of the box if they are made available when the virtual machine is first provisioned. See https://www.fast-downward.org/QuickStart for more information.

  • A long-standing bug in the computation of derived predicates has been fixed. Thanks to everyone who provided bug reports for their help and for their patience!

  • A new and much faster method for computing stubborn sets has been added to the planner.

  • The deprecated merge strategy aliases merge_linear and merge_dfp have been removed.

Details:

Fast Downward 19.12

Released on December 20, 2019.

Highlights:

  • Fast Downward no longer supports Python 2.7, which reaches its end of support on January 1, 2020. The minimum supported Python version is now 3.6.

  • Fast Downward now supports the SoPlex LP solver.

Details:

Fast Downward 19.06

Released on June 11, 2019. First time-based release.