Fast Downward规划器使用when条件效应报错，求解决方案

问题场景 #

我使用Fast Downward规划器解决PDDL问题时，在domain文件的dfaact动作中通过when语句实现了条件效应。执行命令：

./fast-downward.py tests/gripper_ltlf/prob01.pddl --search "astar(lmcut())"

收到以下错误提示：

"This configuration does not support conditional effects (operator dfaact)!  
Terminating.  
Tried to use unsupported feature.   
Peak memory: 23248 KB  
Remove intermediate file output.sas  
search exit code: 34"

怀疑是所选搜索算法的问题，但作为Fast Downward新手，不清楚如何处理。相关domain和problem文件内容如下：

Domain文件 #

(define (domain gripper-strips)
   (:predicates (room ?r)
        (ball ?b)
        (gripper ?g)
        (at-robby ?r)
        (at ?b ?r)
        (free ?g)
        (carry ?o ?g)
        (world )
        (dfa )
        (q1)(q2)(q3)(q4)
        
)
        
(:action dfaact
       :parameters  ()
       :precondition (and (dfa ))
       :effect (and  (not(dfa )) (world ) 
         (when (and  (q1) (at ball1 roomb) (not(at ball4 roomb)) ) 
                       (and (q3) (not (q1)))
         ) 
         (when (and  (q1) (at ball1 roomb) (at ball4 roomb))
                (and (q4) (not(q1)))
         )
         (when (and  (q1) (at ball4 roomb) (not(at ball1 roomb)))
               (and  (q2) (not(q1)))
         )
         (when (and  (q3) (at ball1 roomb) (at ball4 roomb))
               (and  (q4) (not(q3)))
         )
         (when (and  (q3) (not(at ball1 roomb)))
               (and  (q2) (not(q3)))
         )

        )
)


   (:action move
       :parameters  (?from ?to)
       :precondition (and  (room ?from) (room ?to) (at-robby ?from) (world ))
       :effect (and  (at-robby ?to)
             (not (at-robby ?from))  (not(world )) (dfa ) ))


   (:action pick
       :parameters (?obj ?room ?gripper)
       :precondition  (and  (ball ?obj) (room ?room) (gripper ?gripper)
                (at ?obj ?room) (at-robby ?room) (free ?gripper)(world ))
       :effect (and (carry ?obj ?gripper)
            (not (at ?obj ?room)) 
            (not (free ?gripper))(not(world )) (dfa )))


   (:action drop
       :parameters  (?obj  ?room ?gripper)
       :precondition  (and  (ball ?obj) (room ?room) (gripper ?gripper)
                (carry ?obj ?gripper) (at-robby ?room)(world ))
       :effect (and (at ?obj ?room)
            (free ?gripper)
            (not (carry ?obj ?gripper))(not(world )) (dfa ))))

Problem文件 #

(define (problem strips-gripper-x-1)
   (:domain gripper-strips)
   (:objects rooma roomb ball4 ball3 ball2 ball1 left right)
   (:init (q1)
      (dfa)
      (room rooma)
          (room roomb)
          (ball ball4)
          (ball ball3)
          (ball ball2)
          (ball ball1)
          (at-robby rooma)
          (free left)
          (free right)
          (at ball4 rooma)
          (at ball3 rooma)
          (at ball2 rooma)
          (at ball1 rooma)
          (gripper left)
          (gripper right))
   (:goal (and (q4)
        (at ball4 roomb)
               (at ball3 roomb)
               (at ball2 roomb)
               (at ball1 roomb))))

解决办法 #

1. 更换支持条件效应的搜索算法 #

你使用的lmcut()启发式不支持条件效应，Fast Downward中有多款支持该特性的算法，比如：

• astar(blind())：盲搜索，适合快速验证基础功能
• astar(ff())：经典FF启发式，对条件效应兼容性好
• astar(hmax())：HMAX启发式，同样支持条件效应

以FF启发式为例，修改后的执行命令为：

./fast-downward.py tests/gripper_ltlf/prob01.pddl --search "astar(ff())"

2. 预处理条件效应（可选） #

如果坚持要使用lmcut()，可以将带条件效应的动作拆分为多个无条件效应的独立动作。比如把dfaact中的5个when分支，分别拆成单独的动作，每个动作的前置条件包含原分支的判断条件，效应对应分支的结果。

示例拆分其中一个分支：

(:action dfaact_q1_ball1_roomb_not_ball4
       :parameters  ()
       :precondition (and (dfa) (q1) (at ball1 roomb) (not(at ball4 roomb)))
       :effect (and (not(dfa)) (world) (q3) (not(q1)))
)

将所有分支拆分完成后，lmcut()即可正常处理。

3. 确认Fast Downward基础配置 #

确保使用的Fast Downward版本支持条件效应（官方发行版基本都支持），无需额外编译选项，只需选择对应兼容的搜索算法即可。

内容的提问来源于stack exchange，提问作者Solya