Ensemble motion planning in trees

The problem of transporting a set of objects between the vertices of a tree by a unit capacity vehicle that travels along the edges of the tree is considered. For the case in which any object can be dropped at intermediate vertices along its route and picked up later, the authors present algorithms for finding a minimum cost transportation that run in O(k+qn) time and in O(k+n log n) time, where n is the number of vertices in the tree, k is the number of objects to be moved, and q>