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Re: POP Planner Implementation: Choose-Operator

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  • yougooh2000
    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,
    Message 1 of 7 , Dec 18, 2003
      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. €  â' '¼POP€  â' '½â' '¹s full name is Parital-order
      Planner. It means
      if needs, it is sure that after linearizations of POP plan,
      €  â' '¼Total
      order plans€  â' '½ can be gained.
      > 2. But if you delete the €  â' '¼step 2)€  â' '½, the order
      relationship between start and €  â' '¼P1action€  â' '½ will not be
      written down
      in the €  â' '¼action order set bookkeeping€  â' '½, 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€  â' ¦.., 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
      €  â' '¼RESOLVE-THREATS€  â' '½ and function €  â' '¼POP€  â' '½
      > 1. In the function €  â' '¼POP€  â' '½, procedure
      €  â' '¼CHOOSE-OPERATOR€  â' '½
      and €  â' '¼RESOLVE-THREATS€  â' '½ are closely linked,
      that€  â' '¹s, one by one. It
      means after adding €  â' '¼casual link€  â' '½ and €  â' '¼order
      link€  â' '½ in
      €  â' '¼CHOOSE-OPERATOR€  â' '½, the procedure €  
      â' '¼RESOLVE-THREATS€  â' '½ 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€  â' '¹t exist, The
      €  â' '¼Resolve-threats€  â' '½ doesn€  â' '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´12€  æ'¼'¨12€  æ'·¥ 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'¤Ãª12€  Ã'´Ã'¢12€  Ã'¨Ã'µ 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.
      > >
      > >
      > >
      > > To unsubscribe from this group, send an email to:
      > > aima-talk-unsubscribe@yahoogroups.com
      > >
      > >
      > >
      > > Your use of Yahoo! Groups is subject to
      > http://docs.yahoo.com/info/terms/
      >
      >
      >
      > To unsubscribe from this group, send an email to:
      > aima-talk-unsubscribe@yahoogroups.com
      >
      >
      >
      > Your use of Yahoo! Groups is subject to
      http://docs.yahoo.com/info/terms/
    • chenyu468
      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
      Message 2 of 7 , Dec 18, 2003
        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.
        > > >
        > > >
        > > >
        > > > To unsubscribe from this group, send an email to:
        > > > aima-talk-unsubscribe@yahoogroups.com
        > > >
        > > >
        > > >
        > > > Your use of Yahoo! Groups is subject to
        > > http://docs.yahoo.com/info/terms/
        > >
        > >
        > >
        > > To unsubscribe from this group, send an email to:
        > > aima-talk-unsubscribe@yahoogroups.com
        > >
        > >
        > >
        > > Your use of Yahoo! Groups is subject to
        > http://docs.yahoo.com/info/terms/
      • 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 3 of 7 , Dec 22, 2003
          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.
          > > > >
          > > > >
          > > > >
          > > > > To unsubscribe from this group, send an email to:
          > > > > aima-talk-unsubscribe@yahoogroups.com
          > > > >
          > > > >
          > > > >
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          > > >
          > > >
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          > > >
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          > > >
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