Download - Planning to Learn, Learning to Plan
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Lecture 3-1 CS251: Intro to AI/Lisp II
Planning to Learn, Learning to Plan
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Lecture 3-1 CS251: Intro to AI/Lisp II
Announcements
• Quiz
• A Review of AI Planning Techniques
• Reading for next time: Cognitive model for planning
• Allegro for Windows
• Project deadline I
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Lecture 3-1 CS251: Intro to AI/Lisp II
What is planning?
“Figuring out what to do next”
• Wumpus agent already does that with:– First-order logic– Resolution
• Shortcomings– Default values– Efficiency
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Lecture 3-1 CS251: Intro to AI/Lisp II
Why do we need planners?
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Lecture 3-1 CS251: Intro to AI/Lisp II
STRIPS Planning
• State space search– Just like the search we saw last quarter
• “It’s all in the operators”
• What does a STRIPS operator look like?
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Lecture 3-1 CS251: Intro to AI/Lisp II
STRIPS Operators
Go(there)
At(here), Path(here, there)
At(there), At(here)
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Lecture 3-1 CS251: Intro to AI/Lisp II
Planning Terminology I
• STRIPS ops – Action description– Precondition– Effect / Postconditions / Add & Delete
• Operator schemata
• When is operator o applicable in situation s?
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Lecture 3-1 CS251: Intro to AI/Lisp II
Planning Terminology II
• The final frontier of planning: space– State (situation) space– Plan space
• Plan space is populated by __________
• Operators– Refine by eliminating plans from the set of
plans under consideration– Modify plans by messing with them
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Lecture 3-1 CS251: Intro to AI/Lisp II
Planning in Plan Space
• NOAH planner (Sacerdoti 1975) was first partial-order planner
• In state space, solution is a path– Series of operators
• In plan space, series of plan transformations– Examples: Expand detail, adding ordering
constraints
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Lecture 3-1 CS251: Intro to AI/Lisp II
Pruning the Search Space
• Cutting down the search space– Means-end analysis– Prioritize goals– Identify interactions– Parallelism
• Abstraction levels– Different approaches– Early: NOAH, ABSTRIPS (Sacerdoti 1973)
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Lecture 3-1 CS251: Intro to AI/Lisp II
A Problem in Plan Space
• The goal: Getting milk, banana and a drill and heading home
• Actions:– Go: From here to there– Buy: We’ve got money
• Good things to know– Hardware stores sell drills– Supermarkets sell milk and bananas
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Lecture 3-1 CS251: Intro to AI/Lisp II
Getting Started
• Start with an initial plan Start
Finish
At(Home) Sells(SM, Banana)
Sells(SM, Milk) Sells(HWS, Drill)
Have(Milk) Have(Banana)Have(Drill) At(Home)
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Lecture 3-1 CS251: Intro to AI/Lisp II
Next Step
Start
Finish
At(s) Sells(s, Drill) At(s) Sells(s, Milk)
Have(Drill) Have(Milk) At(Home) Have(Banana)
Buy(Drill) Buy(Milk) Buy(Bananas)
At(s) Sells(s, Bananas)
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Lecture 3-1 CS251: Intro to AI/Lisp II
What have we got?
• Protection– Need to have drill– Buy drill achieves Have(Drill)– If we mess with drill buying, then …– When doesn’t it matter?
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Lecture 3-1 CS251: Intro to AI/Lisp II
And after that...
Start
Finish
At(HWS) Sells(HWS, Drill) At(SM) Sells(SM, Milk)
Have(Drill) Have(Milk) At(Home) Have(Banana)
Buy(Drill) Buy(Milk) Buy(Bananas)
At(SM) Sells(SM, Bananas)
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Lecture 3-1 CS251: Intro to AI/Lisp II
What’s the problem?
• Need to:– Go from home to hardware store– Go from home to supermarket
• Pick one and then...
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Lecture 3-1 CS251: Intro to AI/Lisp II
Interactive Problems
• Big red arrows are protected links
• Protected from … threats
• Change the ordering
• The problem in the abstract– Suppose S1 achieves c for S2
– Now S3 comes along and clobbers c
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Lecture 3-1 CS251: Intro to AI/Lisp II
Project topics
• Planning– Build a planner from scratch: (AB)STRIPS,
NOAH– Explore current planners
• Robotics– Investigate reactive planning: write a series
of RAPs– “Build” a robot using subsumption
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Lecture 3-1 CS251: Intro to AI/Lisp II
Project Topics II
• Perception– Explore audio perception– Write an object recognizer (Pepsi cans in
Wayne’s World)
• Machine learning– Look at data mining (name & email from
newsgroup sigs)
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Lecture 3-1 CS251: Intro to AI/Lisp II
Project Topics III
• Uncertainty– Build a system that constructs Bayesian
networks– Look at HMMs in speech recognition
• Natural language– Write a story generator– Tell jokes