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Re: POP Planner Implementation: Choose-Operator

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  • yougooh2000
    Chenyu, Thanks for the feedback. As far as the problem is concerned, my tests until now show that I do not need to add the Start
    Message 1 of 7 , Dec 22, 2003
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      Chenyu,

      Thanks for the feedback.

      As far as the problem is concerned, my tests until now show that I do
      not need to add the Start < S-add ordering. I need to test additional
      worlds, but my initial ideia seems to be valid. I don't know if this
      is due to the way in which I implemented the algorithm or some "bug".

      Anyway here is the explanation: because the alg. is goal recursive I
      only check for preconditions before I regress. If after an
      operation/step has been selected I do not add Start < S-add, it does
      not matter because I only check for the steps/operators that I have
      selected until now with open preconditions. Start will therefore never
      be considered, it has no pre-conds.

      What about checking for consistency? This doesn't matter either
      because I cannot promote anything before Start, nor for that matter
      demote it after Finish. In other words consistency only checks for
      steps consistency between Start and Finish (exclusive).

      What about identifying threats? Just as in the case checking for
      consistency, threats may only occur for operators/steps between Start
      and Finish. So once again, if I do add a Start < S-add, I don't need
      the info to identify threats.
      Please note that the book's algo. just checks if an operator/step
      "clobbers" anothers pre-conds. This means that after ordering, the
      check for threats will still show the threats. I only use ordering
      information so as not to repeatedly (and unecessarily) resolve
      conflicts.

      I hope this explanation is valid. In case I do detect a mistake, I
      will post additional information.

      Thanks again.
      Regards,
      Hugo.




      --- In aima-talk@yahoogroups.com, "chenyu468" <chenyu468@y...> wrote:
      > Hello Hugo,
      > I have use "notepad" to format the reply and eliminate the special
      > characters. I hope it is readable now.
      >
      > In addition, for your program's problem (don't work), maybe firstly
      > test the simplest planning problem as follows (context) to find the
      > error, then comparing with the pceudo-code to find the problem. I
      > haven't start this implementation now.
      >
      >
      > kind regards/chenyu
      >
      >
      >
      >
      > ;;;;;;;;;;;;;;;;;
      > ;;last message
      > ;;;;;;;;;;;;;;;;;
      > I have read the pecudo code again give you my thinking here. If you
      > delete the step 2) (start < s-add < finish), the following problem
      > will happens, To make the discussion more clearly, I give the
      context
      > (To simplify the problem, I will ignore the variables):
      >
      > Context:
      >
      > 1. actions
      > a) action1
      > i. name: start
      > ii. precondition: nothing
      > iii. effect: nothing
      > b) action2
      > i. name: finish
      > ii. precondition: predicate
      > iii. effect: nothing
      > c) action3
      > i. name: P1action
      > ii. precondition nothing
      > iii. effect: predicate
      > 2. initial casual link set bookkeeping
      > a) empty set
      > 3. initial action order set bookkeeping
      > a) start < finish
      >
      > Problem and discussion:
      > 1. Problem:
      > a) Is it possible for you to delete the step 2)
      > (start < s-add < finish)?
      > 2. discussion:
      > a) Not correct.
      > b) My reason:
      > i. Requirement of Linearization:
      > 1. "POP"'s full name is Parital-
      > order Planner. It means if needs, it is sure that after
      > linearizations of POP plan, "Total order plans" can be gained.
      > 2. But if you delete the "step
      > 2)", the order relationship between start and "P1action" will not
      be
      > written down in the "action order set bookkeeping", it is difficult
      > for the above linearizations operation.
      > 3. In last 2nd paragraph of page
      > 350 (AIMA version 1), light arrows in the figure show ordering
      > constraints¡­.., Also, all causes are constrained to come before
      > their effects, so you can think of each bold arrow as having a
      light
      > arrow underneath it.
      > ii. Requirement of procedure "RESOLVE-
      > THREATS" and function "POP"
      > 1. In the function "POP",
      > procedure "CHOOSE-OPERATOR" and "RESOLVE-THREATS" are closely
      linked,
      > that¡¯s, one by one. It means after adding "casual link" and
      "order
      > link" in "CHOOSE-OPERATOR", the procedure "RESOLVE-THREATS" will
      > check the threat has been happened or not. If happens, It will try
      to
      > solve it immediately. This immediately check needs the ordering
      > information. And the solving of threat also needs the ordering
      > information.
      > 2. If the ordering information
      > doesn¡¯t exist, The "Resolve-threats" doesn¡¯t work.
      >
      >
      > I am also interested in the POP implementation for fully
      > understanding and research later, but I want to use lisp language.
      >
      >
      > Kind regards/chenyu
      >
      >
      >
      > --- In aima-talk@yahoogroups.com, "yougooh2000"
      <hugo.ferreira@m...>
      > wrote:
      > > Hi Chenyu,
      > >
      > > Thanks for the feedback. Unfortunatelly I could not understand
      much
      > of
      > > your example. I cannot read the characters 8-(. As far as
      > > linearization goes, you are correct: to check and handle threats I
      > > need to have the correct orderings. My initial implementation
      (which
      > > is still not working), does insert the S-add < Finish because it
      > > regards Start as a standard step in the plan when selecting a
      > > sub-goal. As far as Start < S-add I have to check on that and see
      > how
      > > it influences threat detection and resolution. Nevertheless
      because
      > I
      > > also handle Finish as a step I do get a Start < S-add, but not in
      > the
      > > same point in time.
      > >
      > > Regards,
      > > Hugo F.
      > >
      > >
      > >
      > > --- In aima-talk@yahoogroups.com, E etech058 <etech058@o...>
      wrote:
      > > > Hello,
      > > > I have read the pecudo code again give you my thinking here. If
      > you
      > > delete the step 2) (start < s-add < finish), the following problem
      > > will happens, To make the discussion more clearly, I give the
      > context
      > > (To simplify the problem, I will ignore the variables):
      > > > Context:
      > > > 1. actions
      > > > a) action1
      > > > i. name:
      > start
      > > > ii. precondition:
      nothing
      > > > iii. effect:
      > > nothing
      > > > b) action2
      > > > i. name:
      > finish
      > > > ii. precondition:
      > predicate
      > > > iii. effect:
      > > nothing
      > > > c) action3
      > > > i. name:
      > > P1action
      > > > ii. precondition
      nothing
      > > > iii. effect:
      > > predicate
      > > > 2. initial casual link set bookkeeping
      > > > a) empty set
      > > > 3. initial action order set bookkeeping
      > > > a) start < finish
      > > >
      > > > Problem and discussion:
      > > > 1. Problem:
      > > > a) Is it possible for you to delete the step 2) (start <
      s-
      > add
      > > < finish)?
      > > > 2. discussion:
      > > > a) Not correct.
      > > > b) My reason:
      > > > i. Requirement of
      > > Linearization:
      > > > 1. € ??¼POP€ ??½â'?¹s full name is
      Parital-order
      > > Planner. It means
      > > if needs, it is sure that after linearizations of POP plan,
      > > € ??¼Total
      > > order plans€ ???can be gained.
      > > > 2. But if you delete the € ??¼step 2)€ ???
      the order
      > > relationship between start and € ??¼P1action€
      ???will not be
      > > written down
      > > in the € ??¼action order set bookkeeping€ ??? it is
      difficult
      > > for the
      > > above linearizations operation.
      > > > 3. In last 2nd paragraph of page 350 (AIMA version 1),
      > light
      > > arrows in the figure show ordering constraints€ ? ¦..,
      Also, all
      > > causes
      > > are constrained to come before their effects, so you can think of
      > each
      > > bold arrow as having a light arrow underneath it.
      > > > ii. Requirement of procedure
      > > € ??¼RESOLVE-THREATS€ ???and function €
      ??¼POP€ ???> >
      > 1. In the function € ??¼POP€ ??? procedure
      > > € ??¼CHOOSE-OPERATOR€ ???> and €
      ??¼RESOLVE-THREATS€ ???are
      > closely linked,
      > > that€ ??¹s, one by one. It
      > > means after adding € ??¼casual link€ ???and €
      ??¼order
      > > link€ ???in
      > > € ??¼CHOOSE-OPERATOR€ ??? the procedure €
      > > ??¼RESOLVE-THREATS€ ???will check
      > > the threat has been happened or not. If happens, It will try to
      > solve
      > > it immediately. This immediately check needs the ordering
      > information.
      > > And the solving of threat also needs the ordering information.
      > > > 2. If the ordering information doesn€ ??¹t
      exist, The
      > > € ??¼Resolve-threats€ ???doesn€ ??¹t work.
      > > >
      > > >
      > > > I am also interested in the POP implementation for fully
      > > understanding and research later, but I want to use lisp language.
      > > >
      > > >
      > > > Kind regards/chenyu
      > > >
      > > > -----Original Message-----
      > > > From: yougooh2000 [mailto:hugo.ferreira@m...]
      > > > Sent: 2003€ å¹?2€ ???2€ ?·¥ 17:18
      > > > To: aima-talk@yahoogroups.com
      > > > Subject: [aima-talk] Re: POP Planner Implementation: Choose-
      > Operator
      > > >
      > > > Hi,
      > > >
      > > > First versions will (hopefully) be in Prolog. This is for
      research
      > > > purposes.
      > > >
      > > > Regards,
      > > > Hugo.
      > > >
      > > >
      > > > --- In aima-talk@yahoogroups.com, E etech058 <etech058@o...>
      > wrote:
      > > > > Hello,
      > > > > Which language will you use for implementation?
      > > > >
      > > > > Best regards/chenyu
      > > > >
      > > > > -----Original Message-----
      > > > > From: yougooh2000 [mailto:hugo.ferreira@m...]
      > > > > Sent: 2003€ ?¤Ã?2€ ?´Ã'?2€ ?¨Ã'?0:06
      > > > > To: aima-talk@yahoogroups.com
      > > > > Subject: [aima-talk] POP Planner Implementation:
      Choose-Operator
      > > > >
      > > > > Hi,
      > > > >
      > > > > I am attempting to implement the POP planner as is described
      in
      > > > AIMA's
      > > > > 1st version (Chap. 11.). I am having doubts regarding the call
      > > > > "choose-operator" that is described in the book. The
      > > > > pseudo-code says
      > > > > that if the step to add (S-add) is selected from operator's
      list
      > > > (not
      > > > > the plan), then it is necessary to:
      > > > > 1)Add this new step to the plans already existing steps.
      > > > > 2)Add the ordering: Start < S-add < Finish
      > > > >
      > > > > I cannot understand what is the need for step 2). Say for
      > example
      > > I
      > > > > start the planner with a minimal plan of {Start, Finish} and
      on
      > > > > selecting the first operator, I only find an S-add from the
      > > > operator's
      > > > > list. I will have to add the ordering S-add < S-need, where
      > > S-need =
      > > > > Finish, according to the 5th pseudo-code line of the call.
      After
      > > > that
      > > > > I see that I have to execute steps 1 and 2 as described above.
      > > Now I
      > > > > have a _repeated_ attempt to add ordering S-add < Finish.
      > > > >
      > > > > I have considered not doing step 2) which would result in a
      > > missing
      > > > > ordering Start < S-add. I figure this will eventually be
      added
      > to
      > > > the
      > > > > orderings when I process step S-add (i.e: attempt to satisfy
      its
      > > > > pre-conditions).
      > > > >
      > > > > Am I missing something?
      > > > >
      > > > > TIA.
      > > > > Hugo Ferreira.
      > > > >
      > > > >
      > > > >
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