Tunable Suboptimal Heuristic Search

Finding optimal solutions to state-space search problems often takes too long, even when using A* with a heuristic function. Instead, practitioners often use a tunable approach, such as weighted A*, that allows them to adjust a trade-off between search time and solution cost until the search is sufficiently fast for the intended application. In this paper, we study algorithms for this problem setting, which we call `tunable suboptimal search'. We introduce a simple baseline, called Speed*, that uses distance-to-go information to speed up search. Experimental results on standard search benchmarks suggest that 1) bounded-suboptimal searches suffer overhead due to enforcing a suboptimality bound, 2) beam searches can perform well, but fare poorly in domains with dead-ends, and 3) Speed* provides robust overall performance.