This article is about a search algorithm. For the digital voice d&d valentines gifts data protocol specification, see D-STAR.

For the physical quantity, see Specific detectivity. For the subatomic particle, see hexaquark. Anthony Stentz, is an informed incremental search algorithm. All three search algorithms solve the same assumption-based path planning problems, including planning with the freespace assumption, where a robot has to navigate to given goal coordinates in unknown terrain. The algorithm works by iteratively selecting a node from the OPEN list and evaluating it. It then propagates the node’s changes to all of the neighboring nodes and places them on the OPEN list. This propagation process is termed “expansion”.

Green indicates nodes which are being expanded. The path is indicated in cyan. When an obstruction is detected along the intended path, all the points that are affected are again placed on the OPEN list, this time marked RAISE. Before a RAISED node increases in cost, however, the algorithm checks its neighbors and examines whether it can reduce the node’s cost. If not, the RAISE state is propagated to all of the nodes’ descendants, that is, nodes which have backpointers to it.

These nodes are then evaluated, and the RAISE state is passed on, forming a wave. By this point, a whole series of other points are prevented from being “touched” by the waves. The algorithm has therefore only worked on the points which are affected by change of cost. Yellow indicates nodes marked RAISE, green indicates nodes marked LOWER. This time, the deadlock cannot be bypassed so elegantly. None of the points can find a new route via a neighbor to the destination. Therefore, they continue to propagate their cost increase.

Only points outside of the channel can be found, which can lead to destination via a viable route. This is how two Lower waves develop, which expand as points marked as unattainable with new route information. RAISE and LOWER toward the robot. Koenig and Likhachev few years earlier.