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== Setting the "cost type" for landmark heuristics == == Using "preferred operators" with landmark heuristics ==
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For mostly historical reasons, specifying the cost type (see HeuristicSpecification) for landmark heuristics is currently complicated. Here's the complete set of rules: Unlike all other (current) heuristics, the landmark heuristics ({{{landmark_sum}}} and {{{landmark_cost_partitioning}}}, see [[Doc/Evaluator#Landmark_sum_heuristic]] and [[Doc/Evaluator#Landmark_cost_partitioning_heuristic]]) require a special setting {{{pref=true}}} to enable preferred operator support. Hence, to use preferred operators with these heuristics, '''two''' things must be done at the moment:
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=== If you use the LAMA-FF synergy ===

There are three relevant options:

 1. {{{lm_cost_type}}} of the landmark generation method (e.g. {{{lm_rhw}}})
 2. {{{cost_type}}} of the landmark generation method (e.g. {{{lm_rhw}}})
 3. {{{cost_type}}} of the synergy declation ({{{lm_ff_syn}}})

The cost type of the synergy's landmark heuristic is determined by option 1. when using {{{admissible=false}}} and by option 3. when using {{{admissible=true}}}.

The cost type of the synergy's FF heuristic is determined by option 2. /!\

=== If you do not use the LAMA-FF synergy ===

There are three relevant options:

 1. {{{lm_cost_type}}} of the landmark generation method (e.g. {{{lm_rhw}}})
 2. {{{cost_type}}} of the landmark generation method (e.g. {{{lm_rhw}}})
 3. {{{cost_type}}} of the landmark heuristic declation ({{{lmcount}}})

The cost type of the landmark heuristic is determined by option 1. when using {{{admissible=false}}} and by option 3. when using {{{admissible=true}}}.

Option 2 is ignored in this case.
 1. Set {{{pref=true}}} in the [[Doc/Evaluator| heuristic specification]].
 2. Include the heuristic in the list of heuristics in the {{{preferred}}} specification of the [[Doc/SearchEngine|search engine]].

Back to the HomePage.

Caveats for the options

Here, we document some aspects of the command-line syntax that may be unintuitive or complicated.

Using "preferred operators" with landmark heuristics

Unlike all other (current) heuristics, the landmark heuristics (landmark_sum and landmark_cost_partitioning, see Doc/Evaluator#Landmark_sum_heuristic and Doc/Evaluator#Landmark_cost_partitioning_heuristic) require a special setting pref=true to enable preferred operator support. Hence, to use preferred operators with these heuristics, two things must be done at the moment:

  1. Set pref=true in the heuristic specification.

  2. Include the heuristic in the list of heuristics in the preferred specification of the search engine.