Computing push plans for disk-shaped robots

Suppose we want to move a passive object along a given path, among obstacles in the plane, by pushing it with an active robot. We present two algorithms to compute a push plan for the case that the obstacles are non-intersecting line segments, and the object and robot are disks. The first algorithm assumes that the robot must maintain contact with the object at all times, and produces a shortest path. There are also situations, however, where the robot has no choice but to let go of the object occasionally. Our second algorithm handles such cases, but no longer guarantees that the produced path is the shortest possible

Computing push plans for disk-shaped robots

Suppose we want to move a passive object along a given path, among obstacles in the plane, by pushing it with an active robot. We present two algorithms to compute a push plan for the case that the obstacles are non-intersecting line segments, and the object and robot are disks. The first algorithm assumes that the robot must maintain contact with the object at all times, and produces a shortest path. There are also situations, however, where the robot has no choice but to let go of the object occasionally. Our second algorithm handles such cases, but no longer guarantees that the produced path is the shortest possible

Large bichromatic point sets admit empty monochromatic 4-gons

We consider a variation of a problem stated by Erd˝os and Szekeres in 1935 about the existence of a number fES(k) such that any set S of at least fES(k) points in general position in the plane has a subset of k points that are the vertices of a convex k-gon. In our setting the points of S are colored, and we say that a (not necessarily convex) spanned polygon is monochromatic if all its vertices have the same color. Moreover, a polygon is called empty if it does not contain any points of S in its interior. We show that any bichromatic set of n ≥ 5044 points in R2 in general position determines at least one empty, monochromatic quadrilateral (and thus linearly many).Postprint (published version