Powerlifted Planner

Powerlifted is a domain-independent classical planner that uses only lifted representations.

The planner supports the STRIPS formalism, but extended with inequalities (e.g., (not (= ?x ?y))), types (e.g., ?b - block), and object creation (e.g., :new ?b - block).

(See References for more details.)

Usage

The powerlifted.py script solves a PDDL task provided as input. It also builds the planner if the --build parameter is passed. To run a single search, you can use the following algorithms:

$ ./powerlifted.py [-d DOMAIN] -i INSTANCE -s SEARCH -e EVALUATOR -g GENERATOR [ADDITIONAL OPTIONS] [--build]

The options for each parameter are described below. If you do not pass any value for SEARCH, EVALUATOR, and GENERATOR, the planner will use the best (known) configuration for satisficing planning (i.e., no optimality guaranteed). (See next section for more details.)

It is also possible to perform multiple search algorithms on the same task iteratively. See the section "Multiple Search Algorithms" below.

You can either use the build.py script to build the planner first, or pass the --build flag to build the planner prior to the search execution.

Best Configuration for Satisficing Planning

Currently, the best configuration for satisficing planning (with respect to total coverage) is the following:

$ ./powerlifted.py [-d DOMAIN] -i INSTANCE -s alt-bfws1 -e ff -g yannakakis [ADDITIONAL OPTIONS] --only-effects-novelty-check

These are also the default values for -s, -e, and -g. To maximize coverage, we also recommend adding --unit-cost (see below) to the ADDITIONAL OPTIONS.

Available Options for SEARCH:

• alt-bfws1 and alt-bfws2: [R_x, h] with w=1 and w=2, respectively. The choice of h is given the EVALUATOR option. (See Corrêa and Seipp 2022.)
• astar: A* Search
• bfs: Breadth-First Search (This option was previously called naive. You can still use naive with the powerlifted.py script but the planner will internally use the new keyword bfs.)
• bfws1 and bfws2: Best-First Width Search with w=1 and w=2, respectively.
• bfws1-rx and bfws2-rx: BFWS(R_x) with w=1 and w=2, respectively. (See Corrêa and Seipp 2022.)
• dq-bfws1-rx and dq-bfws2-rx: DQ(R_x) with w=1 and w=2, respectively. (See Corrêa and Seipp 2022.)
• gbfs: Greedy Best-First Search
• iw1 and iw2: Iterated Width Search (with w=1 and w=2, respectively)
• lazy: Lazy Best-First Search
• lazy-po: Lazy Best-First Search with Boosted Dual-Queue
• lazy-prune: Lazy Best-First Search with pruning of states generated by non-preferred operators

Available Options for EVALUATOR:

• add: The additive heuristic
• blind: No Heuristic
• ff: The FF heuristic
• goalcount: The goal-count/STRIPS heuristic
• hmax: The hmax heuristic
• rff: The rule-based FF heuristic

Available Options for GENERATOR:

• join: Join program using the predicate order given in the PDDL file
• random_join: Randomly ordered join program
• ordered_join: Join program ordered by the arity of the predicates
• full_reducer: Generate successor for acyclic schemas using the full reducer method; for cyclic schemas it uses a partial reducer and a join program.
• yannakakis: Same as above but replaces the final join of the full reducer method by the Yannakakis' project-join program.

Available ADDITIONAL OPTIONS:

• [--novelty-early-stop]: Flag if the novelty evaluation of a state should stop as soon as the return value is defined. (See Corrêa and Seipp 2022.)
• [--only-effects-novelty-check]: Flag if the novelty evaluation of a state should only consider atoms in the applied action effect. Warning: for state-of-the-art performance, you must use this option when running BFWS-based search engines. (See Corrêa and Seipp 2022.)
• [--plan-file]: Name of the file used to output the plan(s) found. If you are using sequential iterations, the plan found at the x-th iteration will have .x appended to its name.
• [--preprocess-task]: Preprocess domain and problem PDDL files so it is translated into a fragment supported by Powerlifted. You need to have CPDDL installed, and an environment variable CPDDL_BIN pointing to the cpddl/bin directory after it is locally compiled. Note: This is still not fully functional. CPDDL still leaves negated static precondition on the PDDL file, which Powerlifted does not support. Also, it produces two new intermediate files, which now have hardcoded names.
• [--seed RANDOM SEED]: Random seed for the random number generator.
• [--translator-output-file TRANSLATOR_FILE]: Output of the intermediate representation to be parsed by the search component will be saved into TRANSLATOR_FILE. (Default: output.lifted)
• [--unit-cost]: Use unit cost (i.e., all costs are equal to 1) instead of the costs specified in the domain file.
• [--validate]: Runs VAL after a plan is found to validate it. This requires VAL to be added as validate to the PATH.

Multiple Search Algorithms

You can use the flag --iteration to specify one single search iteration for the planner. You can pass as many --iteration arguments as you wish, and each argument will execute a different search.

The syntax to specify a search iteration is the following:

$ ./powerlifted.py -i INSTANCE --iteration S,E,G

where S is a search algorithm, E is an evaluator, and G a successor generator. For example, to execute Greedy Best-First Search with FF followed by a Lazy Best-First Search with the additive heuristic (and both using the Yannakakis' algorithm for successor generation), you should run

$ ./powerlifted.py -i INSTANCE --iteration gbfs,ff,yannakakis --iteration lazy,add,yannakakis

The plan founds are then numbered based on its iterations. If the first iteration finds a plan, it will be called plan.1; the second will be called `plan.2; etc.

Unfortunately, the planner has the limitation that additional options are set for all the iterations.

Object Creation

Powerlifted supports object creation as part of object effects. The precise semantics are described in [5]. Currently, Powerlifted only supports a STRIPS-like fragment of the problem where action effects can have the following form:

:effect (:new (?o - some-type) (CONJ-EFFECT))

where CONJ-EFFECT is a conjunctive PDDL effect (e.g., (and (p ?x ?y) (p ?y ?o))) where ?o occurs. The basic semantics is that variable ?o must be instantiated with a fresh object that does not exist on the state the the (ground) action is applied.

Unfortunately, not all features of the planner support object creation. Here is a list of features that do support it:

• search engines:
• evaluators:
• successor generators:

See this repository for domain examples.

Running Powerlifted as a Apptainer container

You can also build an Apptainer image to run the planner. This might be useful in the case where you are not able to compile the planner locally, for example. You can run the following command to create the planner image:

apptainer build powerlifted.sif Apptainer.powerlifted

Be aware that this might take a while. Once the image powerlifted.sif is created, you can run it with the same parameters as the powerlifted.py script.

Note that VAL and CPDDL are not installed in the container, so it is not possible to use the --validate flag with the image, or to use the CPDDL preprocessor (--preprocess-task). However, you can run VAL with the plan file created by the planner after the execution, and use CPDDL as a standalone to preprocess the task beforehand.

The following command is a usage example on how to run the planner with the Apptainer image:

./powerlifted.sif -i /path/to/instance.pddl

Requirements

• A C++17-compliant compiler
• CMake 3.9+
• Python 3.5+
• Boost

Limitations

• Axioms: not supported
• Conditional effects: not supported
• Negated preconditions: only inequality
• Quantifiers: not supported

References

1. Corrêa, A. B.; Pommerening, F.; Helmert, M.; and Francès, G. 2020. Lifted Successor Generation using Query Optimization Techniques. In Proc. ICAPS 2020, pp. 80-89. [pdf]
2. Corrêa, A. B.; Francès, G.; Pommerening, F.; and Helmert, M. 2021. Delete-Relaxation Heuristics for Lifted Classical Planning. In Proc. ICAPS 2021, pp. 94-102. [pdf]
3. Corrêa, A. B.; Pommerening, F.; Helmert, M.; and Francès, G. 2022. The FF Heuristic for Lifted Classical Planning. In Proc. AAAI 2022. [pdf]
4. Corrêa, A. B.; and Seipp, J. 2022. Best-First Width Search for Lifted Classical Planning. In Proc. ICAPS 2022. [pdf]
5. Corrêa, A. B.; De Giacomo, G.; Helmert, M.; and Rubin, S. 2024. Planning with Object Creation. In Proc. ICAPS 2024. [pdf]