Arithmetic expression in action preconditions

[Luca Faraoni]

Hi all and nice to meet you.

Someone knows if it is possible to write arithmetic expression inside actions preconditions?

Something like this:

(:action load
    :parameters (?f - freight ?v - vehicle ?l - location)
    :precondition (and
        (at1 ?f ?l)
        (at2 ?v ?l)
        (>= (maxLoad) (+ (load ?v) (weight ?f)))
    )
    :effect (and
        (in ?f ?v)
        (increase (load ?v) (weight ?f))

    )

)

For now i got this error: b'Undeclared predicate: >=\n'

Thanks for help!!

Cheers,

Luca

[Florian Pommerening]

Dear Luca,

Fast Downward is a classical planner and does not cover numerical
variables. There are two options to deal with this:

1) If your numerical variables only allow a small finite number of
distinct values, you can model each value as an object. For example, see
how the height of a tower is implemented in the domain TERMES:
https://github.com/aibasel/downward-benchmarks/blob/master/termes-opt18-strips/domain.pddl

2) If option 1 is not practical, you can try a numerical planner. I
suggest asking on the planning slack channel for good suggestions:
https://theplanningcommunity.slack.com/

Cheers
Florian

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