Now consider generalizing the wavefront propagation idea. Wavefront
propagation can be applied to any discrete planning problem if
for any and
(except ). It is
most useful when the transition graph is sparse (imagine representing
the transition graph using an adjacency matrix). The grid problem is
a perfect example where this becomes important. More generally, if
the cost terms assume integer values, then *Dial's algorithm*
[272] results, which is a generalization of wavefront
propagation, and a specialization of Dijkstra's algorithm. The
idea is that the priority queue can be avoided by assigning the alive
vertices to buckets that correspond to different possible
cost-to-go values. In the wavefront propagation case, there are
never more than two buckets needed at a time. Dial's algorithm allows
all states in the smallest cost bucket to be processed in parallel.
The scheme was enhanced in [939] to yield a linear-time
algorithm.

Steven M LaValle 2020-08-14