MIT16_410F10_lec08b

MIT16_410F10_lec08b - 1 Activity Planning II Plan Extraction and Analysis Brian C Williams 16.410-13 October 4 th 2010 Slides draw upon material

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Unformatted text preview: 1 Activity Planning II: Plan Extraction and Analysis Brian C. Williams 16.410-13 October 4 th , 2010 Slides draw upon material from: Prof. Maria Fox Univ Strathclyde, Scotland Brian Williams, Fall 10 2 Assignments • Remember: Problem Set #5: Constraint Satisfaction and Activity Planning, out Wed. Sep. 29 th , due Wed, Oct. 6 th , 2010. • Reading: – Today: Advanced Planning [AIMA] Ch. 11 " GraphPlan, # by Blum & Furst. – Wednesday: Wednesday: Dechter, R., I. Meiri, J. Pearl, “Temporal Constraint Networks,” Artificial Intelligence, 49, pp. 61-95,1991 posted on Stellar . • Exam: – Mid-Term - October 20 th . 2 Example Problem: Dinner Date Initial Conditions : (:init (cleanHands) (quiet)) Goal : (:goal (noGarbage) (dinner) (present)) Actions : (:operator carry :precondition :effect (and (noGarbage) (not (cleanHands))) (:operator dolly :precondition :effect (and (noGarbage) (not (quiet))) (:operator cook :precondition (cleanHands) :effect (dinner)) (:operator wrap :precondition (quiet) :effect (present)) + noops Solution : (Cook, Wrap, Carry) Approach: Graph Plan 1. Construct compact encoding of candidates that prunes many invalid plans – Plan Graph. 2. Generate plan by searching for a consistent subgraph that achieves the goals . Proposition Init State Action Time 1 Proposition Time 1 Action Time 2 3 Plan Graph • Compactly encodes the space of consistent plans, • while pruning . . . 1. partial states and actions at each time i that are not reachable from the initial state. 2. pairs of propositions and actions that are mutually inconsistent at time i. 3. plans that cannot reach the goals. Graph Plan • Create plan graph level 1 from initial state • Loop 1. If goal propositions of the highest level ( nonmutex ), 2. Then search graph for solution • If solution found, then return and terminate. 3. Extend graph one more level. 6 A kin d o f d o u b le se a rch : fo rw a rd d ire ctio n ch e cks n e ce ssa ry (b u t in su fficie n t) co n d itio n s fo r a so lu tio n , ... B a ckw a rd se a rch ve rifie s... 4 Layer 1: Add Proposition Mutexs noGarb cleanH quiet dinner present carry dolly cook wrap cleanH quiet 0 Prop 0 Action 1 Prop 1 Action 2 Prop Do all goal propositions appear non-mutex? No Proposition Mutexs Round 2: Extend the Plan Graph noGarb cleanH quiet dinner present carry dolly cook wrap carry dolly cook wrap cleanH quiet noGarb cleanH quiet dinner present 0 Prop 0 Action 1 Prop 1 Action 2 Prop 5 Search Graph for Solution noGarb cleanH quiet dinner present carry dolly cook wrap carry dolly cook wrap cleanH quiet noGarb cleanH quiet dinner present 0 Prop 0 Action 1 Prop 1 Action 2 Prop Outline • Graph Plan – Solution Extraction – Memos – Properties – Termination with Failure 6 2. Search for a Solution Recursively find consistent actions that achieve all goals at time t, t-1 ... : • Find actions to achieve each goal G i at time t: – For each action A i that makes G i true at t: • If A i isn ! t mutex with a...
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This note was uploaded on 12/26/2011 for the course SCIENCE 16.410 taught by Professor Prof.brianwilliams during the Fall '10 term at MIT.

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MIT16_410F10_lec08b - 1 Activity Planning II Plan Extraction and Analysis Brian C Williams 16.410-13 October 4 th 2010 Slides draw upon material

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