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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. An exception are single-element lists, where the brackets can be dropped. For example, let h1, h2, h3 be heuristic specifications, then [h1, h3], [h2] 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]


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

--heuristic "hff=ff()" --heuristic "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

As of this writing, enumeration arguments can also be specified by number, but this feature is deprecated and should no longer be used.


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 predefine the object.

Heuristic Predefinitions

Heuristics can be predefined using the search option --heuristic (see PlannerUsage#search).

--heuristic name=heuristic

Landmark Predefinitions

If a set of landmarks should be used for several purposes, it can be predefined using the search option --landmarks (see PlannerUsage#search) to avoid duplicate work and memory usage.

--landmarks name=landmarks

Predefinition 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.

--landmarks "lm=lm_hm(m=2)"
--search "iterated([

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 --heuristic "h1=ff()" --heuristic "h2=blind()" \
--if-non-unit-cost --heuristic "h1=cea()" --heuristic "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 2017-05-02 09:18:54 by MalteHelmert)