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l12_13bwgraphx4 - Plan Extraction in GraphPlan Slides draw...

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Brian C. Williams Session 12-13 Plan Extraction in GraphPlan 16.410-13 Slides draw upon material from: Prof. Maria Fox Reading and Assignment for Planning Lectures l ifi Pl i Graph-based P anning AIMA Chapter 11 AIMA = “Art cial Intelligence: A Modern Approach,” by Russell and Norvig. Assignment No problem set out this week, due to mid-term. ease take the pract ce mid-term. Outline Revi GraphPlan Memos Properties ew Solution Extraction Termination with Failure 1
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Simple Spacecraft Problem Observation-1 target instruments Observation-2 Observation-3 Observation-4 calibrated pointing States: Target Pointed To, Camera Calibrated?, Has Image? Operations: Turn, Take Image, and Calibrate. Courtesy of NASA. Example Init Actions Goal p C T y c I A y p C p C p x ¬p x I x Im c p x Operators in STRIPS Representation TakeImage (?target, ?instr): Pre: Status(?instr, Calibrated), Pointing(?target) Eff: Image(?target) Calibrate (?instrument): Pre: Status(?instr, On), Calibration-Target(?target), Pointing(?target) Eff: ¬Status(?inst, On), Status(?instr, Calibrated) Turn (?target): Pre: Pointing(?direction), ?direction ?target Eff: ¬Pointing(?direction), Pointing(?target) ith, NASA Ames Often begin with “?” to denote a parameter, as in ?var. Based on slides by Dave Sm 2
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Partial Order Causal Link Planning ) ion i i i I A F Im c p A I A F p C C Im I A F c p A C p C Im I A F c p A S T A ¬p C C p C Im I A F c p A S p C T A ¬p C C p C Im I A F c p A S p C l l l Planning in the Past: (SNLP, UCPOP 1. Select an open condit 2. Choose an op that can ach eve it Link to an existing nstance Add a new nstance 3. Resolve threats Current P anning: Graph-based P anners (B um & Furst) Outline Revi Memos Properties ew Graph Plan Solution Extraction Termination with Failure Approach: Graph Plan 1. of i Plan Graph. 2. Time 1 Time 1 Time 2 Constructs compact constraint encoding state space from operators and initial state, which prunes many nvalid plans Generates plan by searching for a consistent subgraph that achieves the goals. Proposition Init State Action Proposition Action 3
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Graph Properties A Plan graph plans, 1. i i i . 2. i at ti 3. . compactly encodes the space of consistent while pruning . . . partial states and actions at each t me that are not reachable from the init al state pairs of propositions and actions that are mutually nconsistent me i. plans that cannot reach the goals Example Problem: Dinner Date ions : )) Goal : ions : carry ion ( ion cook ion ( ) (dinner)) ion (quiet) + noops ) Initial Condit (and (cleanHands) (quiet (and (noGarbage) (dinner) (present)) Act (:operator :precondit :effect (and (noGarbage) (not cleanHands))) (:operator dolly :precondit :effect (and (noGarbage) (not (quiet))) (:operator :precondit cleanHands :effect (:operator wrap :precondit :effect (present)) Solution: (Cook, Wrap, Carry Example: Graph and Solution noGarb carry cook wrap carry cook wrap noGarb 0 Prop 1 1 Action 2 Prop cleanH quiet dinner present dolly dolly cleanH quiet cleanH quiet dinner present 0 Action Prop 4
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13 Graphplan Loop 1. If goal ( ) 2. Then If 3.
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