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Option Syntax

Meaning of the call syntax documentation

All parameters can be specified by keyword or by position. Once a parameter is specified by keyword, the rest of the parameters must be specified by keyword too. Some parameters have default values and are optional. These parameters are documented in the form keyword = defaultvalue.

Consider the following example:

name(p, qs, r, s=v1, t=Enum1)

Parameters p, qs and r are mandatory. qs is a list parameter. List parameters have to be enclosed in square brackets. For example, let h1, h2, h3 be heuristic specifications, then [h1, h3] and [h2] are examples for a list of heuristic specifications.

Parameters s and t are optional. s has the default value v1 and t the default value Enum1. t is an enumeration parameter and can only take the values listed (here Enum0, Enum1, Enum2). These values may also be passed by number, e.g. here t=Enum1 and t=1 are equivalent.

Some possible calls for this specification (with X and Xi having type_x):


--help [Name]


Parameters of type int can be specified as "infinity". This means that the parameter will take the value numeric_limits<int>::max(), which is usually equal to 2^31 - 1. If an int parameter value ends with "K", "M" or "G", the value is multiplied by one thousand, one million or one billion, respectively. For example, "bound=2K" is equivalent to "bound=2000".


Parameters of type string can be specified in double quotes. Nested quotes can be escaped as \", backslashes as \\, and newlines as \n. E.g.,



List arguments have to be enclosed in square brackets now. E.g.,

--evaluator "hff=ff()" --evaluator "hcea=cea()" \
--search "lazy_greedy([hff, hcea], preferred=[hff, hcea])" \


Enumeration arguments should be specified by name, e.g.:

eager_greedy([h1,h2], cost_type=normal)

To get enumeration names (and more), run

--help [Name]   //e.g. with Name=eager_greedy


Often an object should be used for several purposes, e.g. a Heuristic or a LandmarkFactory. The most prevalent use case is a heuristic that is used for both the heuristic estimates and for its preferred operators. In this case, one should define a variable for the object. We currently only support variables for Heuristics and LandmarkFactories but will extend the support for other feature types in the future.

Variables can be defined with let(name, definition, expression)

Variable Example

Suppose I want to run GBFS with the lm_count heuristic (the inadmissible version), and then run another GBFS search with an admissible lm_count heuristic, using the h^m landmarks without discovering the landmarks twice.

--search "let(lm, lm_hm(m=2), 

Old-style Predefinitions

We still support but deprecate the use of "predefinitions" before the --search option. They are internally converted to let-expressions.

The command lines

--evaluator name=definition --search expression
--landmarks name=definition --search expression

are both transformed to

--search let(name, definition, expression)

Conditional options

In some cases, it is useful to specify different options depending on properties of the input file. For example, the LAMA 2011 configuration makes use of this, adding an additional cost-ignoring search run at the start for tasks with non-unit action costs.


--if-unit-cost --evaluator "h1=ff()" --evaluator "h2=blind()" \
--if-non-unit-cost --evaluator "h1=cea()" --evaluator "h2=lmcut()" \
--always --search "eager_greedy([h1, h2])"

This conducts an eager greedy search with two heuristics. On unit-cost tasks, it uses the FF heuristic and the blind heuristic. On other tasks, it uses the context-enhanced additive heuristic and the LM-Cut heuristic.


Options can be made conditional via selectors such as --if-unit-cost. All options following a selector are only used if the condition associated with the selector is true. (This really includes all options, including ones like --plan-file that do not affect the planning algorithm.) Each selector is in effect until it is overridden by a new selector. The following selectors are available:

FastDownward: OptionSyntax (last edited 2023-11-22 09:03:02 by GabiRoeger)