Planner founds no plan when a plan exists

[L-Naej]

Hi,

First of all, thanks for this awesome library! I'm learning pddl and started using PDDL4j a few days ago.

It seems the planners have a bug because editor.planning.domains finds a solution to my domain & problem files when pddl4j does not.

I managed to isolate the origin of the error to the following piece of code, which is the precondition of a move action: (or (at ?to ?watcher) (forall (?c - character) (not (at ?to ?c))) )

This disjunction leads to a "No plan found".

However, when I remove the disjunction and just let the "forall" clause, a plan is found. If I understand correctly how disjunctions work, if one of the two clauses is true, then the action should be usable, so the disjunction should not let to a "no plan found". Moreover, editor.planning.domains finds a solution to the problem almost instantly even with the disjunction there.

I tried with -p 0/1/2, but had the same result each time.

The complete action code is as following. Basically I want to force ?watcher to be set so at ?to ?watcher is true if it is possible, else ?watcher can be any character:

(:action move
  :parameters (?character ?watcher - character ?from ?to - place ?characterhouse - house)
  :precondition (and 
                    (at ?from ?character) 
                    ; If someone is in the room, pick it as watcher, else take someone randomly and ignore it in effects (conditional effect).
                    (or 
                        (at ?to ?watcher) 
                         (forall (?c - character) (not (at ?to ?c)))
                    )
                    
                    (not (= ?from ?to))
                    (isfromhouse ?character ?characterhouse)

                    ;Precondition: Either ?to is locked with ?key and ?character possesses ?key, either ?to is not locked.
                    (or 
                        (exists (?key - key) (and (islocked ?to ?key) (possess ?key ?character) ) )
                        (forall (?key - key) (not (islocked ?to ?key)) )
                    )
                    ;Precondition: Either ?to is not reserved to a house, either ?character is from the right house
                    (or 
                        (forall (?h - house) (not (reservedtohouse ?to ?h)) )
                        (reservedtohouse ?to ?characterhouse)    
                    )
                )
 :effect (and 
            (not (at ?from ?character)) 
            (at ?to ?character)
            (when (at ?to ?watcher) (sawatplace ?character ?watcher ?to)) 
        )
)

Do you know where it could come from? Thanks for your help!

[pellierd]

Hi,

Thanks for you return.

Can you join us the domain and the problem that is causing the problem?

Damien

[L-Naej]

Hi Damien, Thanks for your answer. You will find attached the domain and the problem files.

is-harrypotter.txt is-harrypotter-problem.txt

You will see another action, take, which has a similar approach (disjunctive with forall) but seems to work well.

I also tried the GeneralPlannerAnytime with AStarAnytime, same problem. Thanks again,

JN

[L-Naej]

Hi,

I'm still learning pddl4j and now use directly search strategy classes etc, but have been unable to find a working configuration yet. Did you have more luck on your side?

Thanks for your help, JN

[pellierd]

I will try my best to test your problem as soon as possible.