can't find the solution for robot path finding

Question

I'm new to the pddl. I need to find solution where a robot can put different objects in different destination cells. I'm using the software from http://www.fast-downward.org/. However, The problem is that my actions can't find the solution as required. The restriction is that no 2 objects can be in the same room even if the robot is carrying an object. attached: the domain file:

(define (domain gripper-strips)
(:predicates (ROOM ?x) ;iff x is a room
    (OBJECT ?x) ;iff x is an onject
    (HAND ?x) ;iff x is the robot's hand
    (FREE ?x) ;iff x is the robot's hand and it is free of object
    (ROBOT-AT ?x) ;iff x is a room and robot is located in x
    (OBJECT-AT ?x ?y) ;iff x is an object + y is a room and x is located at y
    (PATH ?x ?y) ;iff x and y are both room and there is no wall in-between
    (CARRY ?x) ;iff x is an object and robot is carrying it
)


  (:action MoveWithoutObject
   :parameters  (?room1 ?room2 ?hand)
   :precondition (and  (ROOM ?room1) (ROOM ?room1) (HAND ?hand) (not(=?room1 ?room2))
           (FREE ?hand) (ROBOT-AT ?room1) (PATH ?room1 ?room2))
   :effect (and  (ROBOT-AT ?room2)
         (not (ROBOT-AT ?room1)))
)

 (:action MoveWithObject
   :parameters  (?room1 ?room2 ?obj ?hand)
   :precondition (and  (ROOM ?room1) (ROOM ?room2) (OBJECT ?obj) (HAND ?hand) (not(=?room1 ?room2))
           (not (OBJECT-AT ?obj ?room1)) (not (OBJECT-AT ?obj ?room2))
           (ROBOT-AT ?room1) (not(FREE ?hand))
           (PATH ?room1 ?room2))
   :effect (and  (ROBOT-AT ?room2)
         (not (ROBOT-AT ?room1)))
)

 (:action Pickup
   :parameters (?obj ?room ?hand)
   :precondition  (and  (OBJECT ?obj) (ROOM ?room) (HAND ?hand)
            (OBJECT-AT ?obj ?room) (ROBOT-AT ?room) (FREE ?hand) (not(CARRY ?obj)))
   :effect (and (CARRY ?obj) (not (OBJECT-AT ?obj ?room)) (not (FREE ?hand)))
)

 (:action Release
   :parameters  (?obj ?room ?hand)
   :precondition  (and (OBJECT ?obj) (ROOM ?room) (HAND ?hand)
            (not(OBJECT-AT ?obj ?room)) (ROBOT-AT ?room) (not(FREE ?hand)) (CARRY ?obj))
   :effect (and (OBJECT-AT ?obj ?room)
        (not(CARRY ?obj))
        (FREE ?hand))))

and the problem file:

(define (problem strips-gripper-x-8)
(:domain gripper-strips)
(:objects room1 room2 room3 room4 room5 room6 room7 room8 room9
     object1 object2 object3
         hand)

  (:init (ROOM room1)(ROOM room2)(ROOM room3)(ROOM room4)(ROOM room5)(ROOM room6)(ROOM room7)(ROOM room8)(ROOM room9)
  (OBJECT object1)(OBJECT objec21)(OBJECT object3)
  (HAND hand)
  (FREE hand)
  (ROBOT-AT room1)
  (OBJECT-AT object1 room6)(OBJECT-AT object2 room4)(OBJECT-AT object3 room7)
  (PATH room1 room4)(PATH room4 room1)
  (PATH room4 room5)(PATH room5 room4)
  (PATH room5 room6)(PATH room6 room5)
  (PATH room5 room8)(PATH room8 room5)
  (PATH room6 room9)(PATH room9 room6)
  (PATH room6 room3)(PATH room3 room6)
  (PATH room3 room2)(PATH room2 room3)
  (PATH room8 room7)(PATH room7 room8))

  (:goal (and (OBJECT-AT object1 room7)(OBJECT-AT object2 room2)(OBJECT-AT object3 room9))))

http://www.fast-downward.org/IpcPlanners – Istiaque Hassan Apr 23 '16 at 06:39 — Istiaque Hassan, Apr 23 '16 at 06:39

Patrick Trentin · Accepted Answer · 2016-05-18T06:30:28.820

Your approach is seemingly correct, but you have a couple of typos in your files that hinder the possibility of finding a solution.

problem.pddl:

change

(OBJECT object1)(OBJECT objec21)(OBJECT object3)

with

(OBJECT object1) (OBJECT object2) (OBJECT object3)

domain.pddl: change

change

(ROOM ?room1) (ROOM ?room1)

in action MoveWithoutObject with

(ROOM ?room1) (ROOM ?room2)

EDIT:

This escaped my first check since I didn't know the language in the first place and I assumed there was an universal quantification over the variables. You also need to fix MoveWithObject like this:

(:action MoveWithObject
 :parameters  (?room1 ?room2 ?obj1 ?obj2 ?obj3 ?hand)
 :precondition (and  (ROOM ?room1) (ROOM ?room2) (HAND ?hand) (not(=?room1 ?room2))
   (OBJECT ?obj1) (OBJECT ?obj2) (OBJECT ?obj3) 
   (not (OBJECT-AT ?obj1 ?room1)) (not (OBJECT-AT ?obj1 ?room2))
   (not (OBJECT-AT ?obj2 ?room1)) (not (OBJECT-AT ?obj2 ?room2))
   (not (OBJECT-AT ?obj3 ?room1)) (not (OBJECT-AT ?obj3 ?room2))
   (not (= ?obj1 ?obj2))
   (not (= ?obj1 ?obj3))
   (not (= ?obj2 ?obj3))
   (ROBOT-AT ?room1) (not (FREE ?hand)) (PATH ?room1 ?room2))
   :effect (and  (ROBOT-AT ?room2)
         (not (ROBOT-AT ?room1)))
)

Now the solver finds the following solution:

    Solution found!
    Actual search time: 2.23336s [t=4.41504s]
    movewithoutobject room1 room4 hand (1)
    movewithoutobject room4 room5 hand (1)
    movewithoutobject room5 room6 hand (1)
    pickup object1 room6 hand (1)
    movewithobject room6 room3 object1 object2 object3 hand (1)
    release object1 room3 hand (1)
    movewithoutobject room3 room6 hand (1)
    movewithoutobject room6 room5 hand (1)
    movewithoutobject room5 room8 hand (1)
    movewithoutobject room8 room7 hand (1)
    pickup object3 room7 hand (1)
    movewithobject room7 room8 object1 object2 object3 hand (1)
    movewithobject room8 room5 object1 object2 object3 hand (1)
    movewithobject room5 room6 object1 object2 object3 hand (1)
    movewithobject room6 room9 object1 object2 object3 hand (1)
    release object3 room9 hand (1)
    movewithoutobject room9 room6 hand (1)
    movewithoutobject room6 room3 hand (1)
    pickup object1 room3 hand (1)
    movewithobject room3 room6 object1 object2 object3 hand (1)
    movewithobject room6 room5 object1 object2 object3 hand (1)
    movewithobject room5 room8 object1 object2 object3 hand (1)
    movewithobject room8 room7 object1 object2 object3 hand (1)
    release object1 room7 hand (1)
    movewithoutobject room7 room8 hand (1)
    movewithoutobject room8 room5 hand (1)
    movewithoutobject room5 room4 hand (1)
    pickup object2 room4 hand (1)
    movewithobject room4 room5 object1 object2 object3 hand (1)
    movewithobject room5 room6 object1 object2 object3 hand (1)
    movewithobject room6 room3 object1 object2 object3 hand (1)
    movewithobject room3 room2 object1 object2 object3 hand (1)
    release object2 room2 hand (1)
    Plan length: 33 step(s).
    Plan cost: 33

I used the following strategy for finding this solution, other strategies might find longer paths:

 $ fast-downward.py --alias seq-opt-bjolp problem.pddl

Thanks. it is a good progress. but the solution seems not right as it can't release the old object before picking up new one and it seems to have 2 objects in the same room when robot moveswithobject. For example: robot pickup the object2 from room4 then the next line says that robot moves from room4 to 5 with object1. — Istiaque Hassan, Apr 23 '16 at 13:23
@IstiaqueHassan I have edited my answer with the requested fixes — Patrick Trentin, Apr 23 '16 at 14:27

can't find the solution for robot path finding

1 Answers1