**4. Search-based replanning on time-varying environment**

In real-world application, there is often a scenario that the robot initially does not know a priori information about its surroundings. We cannot encode the world space information each time the robot runs, because it is expensive, tedious, and infeasible due to rapid changes in practice. To maintain collision-free path, one can naively rerun A\* to replan the shortest path from the point that the robot detects changes. However, this naïve approach will waste computation by reprocessing cells that are irrelevant to compute a new path and hence increase idle time between each search. This section will demonstrate search-based algorithms to solve mentioned problem in time-variant environment.
