All planning problems involve a sequence of
decisions that must be applied over time. Time might be explicitly
modeled, as in a problem such as driving a car as quickly as possible
through an obstacle course. Alternatively, time may be implicit, by
simply reflecting the fact that actions must follow in succession, as
in the case of solving the Rubik's cube. The particular time is
unimportant, but the proper sequence must be maintained. Another
example of implicit time is a solution to the Piano Mover's Problem;
the solution to moving the piano may be converted into an animation
over time, but the particular speed is not specified in the plan. As
in the case of state spaces, time may be either discrete or
continuous. In the latter case, imagine that a continuum of decisions
is being made by a plan.
Steven M LaValle
2020-08-14