Lecture11HO - CS440/ECE448 Intro to Articial Intelligence...

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Lecture 11: Planning Prof. Julia Hockenmaier [email protected] http://cs.illinois.edu/fa11/cs440 CS440/ECE448: Intro to Artificial Intelligence What is planning? What is planning? Plan = ʻ plan of attack ʼ : Use inference to find a sequence of actions to reach a goal state from the initial state Combines logic and search: Logic: to describe states and define actions Search: to find the actual sequence of actions Applications of planning Space exploration Manufacturing Games (Bridge) Scheduling Logistics Semantic web support 4 CS440/ECE448: Intro AI
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Main types of planners Domain-specific: Tuned to target domain; don ʼ t generalize; used in real-world applications ( In CS440): domain-independent planning the only domain-specific knowledge: definitions of basic actions; requires many simplifying assumptions; = classical planning 5 CS440/ECE448: Intro AI Classical planning: assumptions The environment is: Fully observable Deterministic Static Known Finite (finitely many states and actions) Under these assumptions, a plan is a linear sequence of actions, and planning can be done off-line 6 CS440/ECE448: Intro AI Classical planning State transition system ! = (S, A, ! ) S = {states} A = {actions} ! = S " A # 2 S {state transition function) Initial state: s 0 Set of goal states: S g Task: Given ( ! , s 0 , S g ) , find a sequence of actions (a 1 ,a 2 ,…,a n-1 ,a n ) that produces a sequence of state transitions (s 1 ,s 2 ,…,s n-1 ,s n ) such that s n S g . 7 CS440/ECE448: Intro AI State transition system ! = (S,A, ! ) Classical Planning Planner Solution (= sequence of actions) (a 1 ,a 2 ,…,a n-1 ,a n ) Initial state s 0 Goal specification (description of goal states) S g
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Blocks World Goals: Build a tower of A,B,C,… Get block G, …. Silly domain, but concisely illustrates many general planning issues B D E G C F A B Granularities of representations: Blocks World Several ontologies possible (ways to conceptualize the world and its changes) D E G C F A Alternative Ontologies: how to move a block Version 1: MoveBlock Version 2: MoveGripper GraspBlock MoveGripper UngraspBlock Version 3: MoveGripper OpenGripper MoveGripper CloseGripper Version 4: Motor1 Velocity Motor2 Velocity Version 5: Motor1-Voltage (current, dutycycle) …. 11 CS440/ECE448: Intro AI Levels of Ontological Commitment Abstract, High-Level Ontology Action(Achieve-Block-Configuration3) Problem is trivialized Mid-Level Ontology MoveBlock( ... ) Low-Level Ontology Action(Motor3, Voltage7) Artificially and unnecessarily difficult Assume we ʼ re here Planning Assumed Hardware Support
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Traditional Blocks World Only support relationships matter (and change): On(x,y) (x is on y) , Clr(x) (x is clear) Assumptions: A block can support at most one other block The table can support any number of blocks Generalized block movement move(x,y,z) B D E G C F A I I,a2,a34 All reachable situations are defined by… I,a2 I,a17 I,a4 I,a15 1) The initial state
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