TCA*-a time-constrained approximate A* search algorithm

The authors develop TCA*, a family of problem-independent, time-constrained, approximate A* search algorithms. The algorithms are designed to achieve the best ascertained degree of approximation with the minimum cost under a fixed time constraint, where cost is measured by either the cumulative space-time (CST) product or the maximum space encountered during the search. Only A* searches with admissible heuristic functions are considered; a branch-and-bound algorithm with a best-first strategy is an example of such a search. NP-hard combinatorial optimization problems whose feasible solutions can be found easily in polynomial time are studied. For the problems studied, it is observed that the execution time, the CST product and the maximum space required all increase exponentially as the degree of approximation decreases