Journal of Arti cial Intelligence Research 9 1998 1{36 Submitted 1/98; published 8/98 The Computational Complexity of Probabilistic Planning Michael L. Littman
[email protected] Department of Computer Science, Duke University Durham, NC 27708-0129 USA Judy Goldsmith
[email protected] Department of Computer Science, University of Kentucky Lexington, KY 40506-0046 USA Martin Mundhenk
[email protected] FB4 - Theoretische Informatik, Universitat Trier D-54286 Trier, GERMANY Abstract We examine the computational complexity of testing and nding small plans in proba- bilistic planning domains with b oth at and prop ositional representations. The complexity of plan evaluation and existence varies with the plan typ e sought; we examine totally ordered plans, acyclic plans, and lo oping plans, and partially ordered plans under three natural de nitions of plan value. We show that problems of interest are complete for a PP PP variety of complexity classes: PL, P, NP, co-NP, PP,NP , co-NP , and PSPACE. In PP the pro cess of proving that certain planning problems are complete for NP ,weintro duce PP a new basic NP -complete problem, E-Majsat, which generalizes the standard Bo olean satis ability problem to computations involving probabilistic quantities; our results suggest that the development of go o d heuristics for E-Majsat could b e imp ortant for the creation of ecient algorithms for a wide variety of problems. 1. Intro duction Recent work in arti cial-intelligence planning has addressed the problem of nding e ec- tive plans in domains in which op erators have probabilistic e ects Drummond & Bresina, 1990; Mansell, 1993; Drap er, Hanks, & Weld, 1994; Ko enig & Simmons, 1994; Goldman & Bo ddy, 1994; Kushmerick, Hanks, & Weld, 1995; Boutilier, Dearden, & Goldszmidt, 1995; Dearden & Boutilier, 1997; Kaelbling, Littman, & Cassandra, 1998; Boutilier, Dean, & Hanks, 1998.