Abstract
In this paper we study External A*, a variant of the conventional (internal) A* algorithm that makes use of external memory, e.g., a hard disk. The approach applies to implicit, undirected, unweighted state space problem graphs with consistent estimates. It combines all three aspects of best-first search, frontier search and delayed duplicate detection and can still operate on very small internal memory. The complexity of the external algorithm is almost linear in external sorting time and accumulates to \(O(\mbox{\em sort}(|E|) + \mbox{\em scan}(|V|))\) I/O operations, where V and E are the set of nodes and edges in the explored portion of the state space graph. Given that delayed duplicate elimination has to be performed, the established bound is I/O optimal. In contrast to the internal algorithm, we exploit memory locality to allow blockwise rather than random access. The algorithmic design refers to external shortest path search in explicit graphs and extends the strategy of delayed duplicate detection recently suggested for breadth-first search to best-first search. We conduct experiments with sliding-tile puzzle instances.
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References
Aggarwal, A., Vitter, J.S.: Complexity of sorting and related problems. In: Ottmann, T. (ed.) ICALP 1987. LNCS, vol. 267, pp. 467–478. Springer, Heidelberg (1987)
Arge, L., Knudsen, M., Larsen, K.: Sorting multisets and vectors in-place. In: Dehne, F., Sack, J.-R., Santoro, N. (eds.) WADS 1993. LNCS, vol. 709, pp. 83–94. Springer, Heidelberg (1993)
Chiang, Y.-J., Goodrich, M.T., Grove, E.F., Tamasia, R., Vengroff, D.E., Vitter, J.S.: External memory graph algorithms. In: Symposium on Discrete Algorithms (SODA), pp. 139–149 (1995)
Dial, R.B.: Shortest-path forest with topological ordering. Communication of the ACM 12(11), 632–633 (1969)
Hart, P.E., Nilsson, N.J., Raphael, B.: A formal basis for heuristic determination of minimum path cost. IEEE Trans. on on Systems Science and Cybernetics 4, 100–107 (1968)
Korf, R.: Best-first frontier search with delayed duplicate detection. In: National Conference on Artificial Intelligence, AAAI (2004) (to appear)
Korf, R.E.: Depth-first iterative-deepening: An optimal admissible tree search. Artificial Intelligence 27(1), 97–109 (1985)
Korf, R.E.: Divide-and-conquer bidirectional frontier search: First results. In: International Joint Conferences on Artificial Intelligence (IJCAI), pp. 1184–1191 (1999)
Korf, R.E.: Delayed duplicate detection. In: IJCAI-Workshop on Model Checking and Artificial Intelligence, MoChart (2003)
Korf, R.E., Felner, A.: Disjoint Pattern Database Heuristics. In: Chips Challenging Champions: Games, Computers and Artificial Intelligence, pp. 13–26. Elsevier, Amsterdam (2002)
Korf, R.E., Zhang, W.: Divide-and-conquer frontier search applied to optimal sequence allignment. In: National Conference on Artificial Intelligence (AAAI), pp. 910–916 (2000)
Mehlhorn, K., Meyer, U.: External-memory breadth-first search with sublinear I/O. In: European Symposium on Algorithms, ESA (2002)
Meyer, U., Sanders, P., Sibeyn, J.: Memory Hierarchies. Springer, Heidelberg (2003)
Munagala, K., Ranade, A.: I/O-complexity of graph algorithms. In: Symposium on Discrete Algorithms (SODA), pp. 87–88 (2001)
Pearl, J.: Heuristics. Addison-Wesley, Reading (1985)
Zhou, R., Hansen, E.: Breadth-first heuristic search. In: International Conference on Automated Planning and Scheduling (ICAPS), pp. 92–100 (2004)
Zhou, R., Hansen, E.: Structured duplicate detection in external-memory graph search. In: National Conference on Artificial Intelligence, AAAI (2004) (to appear)
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Edelkamp, S., Jabbar, S., Schrödl, S. (2004). External A*. In: Biundo, S., Frühwirth, T., Palm, G. (eds) KI 2004: Advances in Artificial Intelligence. KI 2004. Lecture Notes in Computer Science(), vol 3238. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-30221-6_18
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DOI: https://doi.org/10.1007/978-3-540-30221-6_18
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