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– successor axioms: s Poss(a,s)Eff(result(a,s))• poss_pickup_a_1 pickup_a_1 holding_a_2gripper_empty_2
– frame axioms: s Flu(s)aCancelingActionsFlu(result(a,s))• on_b_c_1 poss_pickup_a_1 on_b_c_2
• use a satisfiability solved like DPLL or WalkSat– query: poss_on_a_b_1? poss_on_a_b_2? poss_on_a_b_3?– the truth values of action propositions in the model tell you the plan
– high-level operators vs. low-level operators– expansion, multiple choices of how to achieve subtask– still a problem of sub-goal interactions– system: STEAM
• plan monitoring and repair– what if action in step i might fail?– non-deterministic domains (most in real-world)– at each step, check pre-conditions– if expected conditions not satisfied, re-invoke planner
• costly to re-plan from scratch• search for modification of existing plan, e.g. re-do previous action or
insert steps to get back on track
• contingent planning: – a plan with a branch in it– include sensor actions to sense state– algorithm to create such plans to achieve goals