Performance of IDA on Trees and Graphs
نویسندگان
چکیده
We present the following results about IDA* and related algorithms: We show that IDA* is not asymptotically optimal in all of the cases where it was thought to be so. In particular, there are trees satisfying all of the conditions previously thought to guarantee asymptotic optimality for IDA*, such that IDA* will expand more than O(N) nodes, where N is the number of nodes eligible for expansion by A*. We present a new set of necessary and suf-cient conditions to guarantee that IDA* expands O(N) nodes on trees. On trees not satisfying the above conditions, there is no best-rst admissible tree search algorithm that runs in S = N==(N) (where (N) 6 = O(1)) memory and always expands O(N) nodes. There are acyclic graphs on which IDA* expands (2 2N) nodes.
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