Usage#

To run Fast Downward, use the fast-downward.py driver script. At minimum, you need to specify the PDDL input files and search options consisting of a search algorithm with one or more evaluator specifications. The driver script has many options to do things like running portfolios, running only the translation component of the planner, using a non-standard build, running a plan validator and various other things. To see the complete list of options, run

./fast-downward.py --help

If you want to run any of the planners based on Fast Downward that participated in IPC 2011, please also check the page on IPC planners.

Caveats#

The search options are built with flexibility in mind, not ease of use. It is very easy to use option settings that look plausible, yet introduce significant inefficiencies. For example, an invocation like

./fast-downward.py domain.pddl problem.pddl --search "lazy_greedy([ff()], preferred=[ff()])"

looks plausible, yet is hugely inefficient since it will compute the FF heuristic twice per state. See the examples at the bottom of this page to see how to call the planner properly. If in doubt, ask.

Different builds#

Different builds of Fast Downward (e.g. release vs. debug) are placed in different directories by the build script. Hence, several builds can coexist and fast-downward.py must be told which build to use. By default, the release build is used, which is also the default build produced by build.py. To use a different build, pass --build=<name> to the driver script. The parameter --debug is an alias for --build=debug --validate.

Note on IDE projects (Visual Studio, XCode): You can use the CMake build system to generate a project for you favourite IDE. These projects are what CMake calls "multi-config generators", i.e., they are created without fixing the build configuration. At build time, the IDE decides whether to do a debug or release build and creates subdirectories in the output folder. Use the full path to the binaries as the value of --build (e.g., --build=path/to/visual/studio/project/bin/Debug/).

Exit codes#

The driver exits with 0 if no errors are encountered. Otherwise, it returns the exit code of the first component that failed (cf. documentation of exit codes).

LP support#

Features that use an LP solver have a command-line option lpsolver to switch between different solver types. See issue752 and issue1076 for a discussion of the relative performance of CPLEX and SoPlex.

Note that SoPlex is not a MIP solver, so using it for configurations that require integer variables will result in an error. Please use CPLEX for such cases.

Examples#

A* search#

# landmark-cut heuristic
 ./fast-downward.py domain.pddl task.pddl --search "astar(lmcut())"

# iPDB heuristic with default settings
 ./fast-downward.py domain.pddl task.pddl --search "astar(ipdb())"

# blind heuristic
 ./fast-downward.py domain.pddl task.pddl --search "astar(blind())"

Lazy greedy best-first search with preferred operators and the queue alternation method#

## using FF heuristic and context-enhanced additive heuristic (previously: "fFyY")
 ./fast-downward.py domain.pddl task.pddl \
    --search "let(hff, ff(), let(hcea, cea(), lazy_greedy([hff, hcea], preferred=[hff, hcea])))"


## using FF heuristic (previously: "fF")
 ./fast-downward.py domain.pddl task.pddl \
    --search "let(hff, ff(), lazy_greedy([hff], preferred=[hff]))"


## using context-enhanced additive heuristic (previously: "yY")
 ./fast-downward.py domain.pddl task.pddl \
    --search "let(hcea, cea(), lazy_greedy([hcea], preferred=[hcea]))"

LAMA 2011#

./fast-downward.py --alias seq-sat-lama-2011 domain.pddl task.pddl

runs the "LAMA 2011 configuration" of the planner. (Note that this is not really the same as "LAMA 2011" as it participated at IPC 2011 because there have been bug fixes and other changes to the planner since 2011. See "IPC planners" for more information.) To find out which actual search options the LAMA 2011 configuration corresponds to, check the source code of the src/driver/aliases.py module.

64-bit mode#

Older planner versions built the planner in 32-bit mode by default because of lower memory consumption. As part of the meta issue issue213 we decreased the memory consumption of 64-bit builds to the point where there should be no difference between 32- and 64-bit builds for most configurations. Therefore, we use the native bitwidth of the operating system since January 2019.