Subproblem ordering heuristics for AND/OR best-first search.

Best-first search can be regarded as anytime scheme for producing lower bounds on the optimal solution, a characteristic that is mostly overlooked. We explore this topic in the context of AND/OR best-first search, guided by the MBE heuristic, when solving graphical models. In that context, the impact of the secondary heuristic for subproblem ordering may be significant, especially in the anytime context. Indeed, our paper illustrates this, showing that a new concept of bucket errors can advise in providing effective subproblem orderings in AND/OR search for both exact and anytime solutions.