We are given a digraph G = (N, A), where each arc is colored with one among k given colors. We look for a spanning arborescence T of G rooted at a given node and having minimum changeover cost. We call this the Minimum Changeover Cost Arborescence problem. To the authorsâ€™ knowledge, it is a new problem. The concept of changeover costs is similar to the one, already considered in the literature, of reload costs, but the latter depend also on the amount of commodity flowing in the arcs and through the nodes, whereas this is not the case for the changeover costs. Here, given any node j different from the root, if a is the color of the single arc entering node j in arborescence T , and b is the color of an arc (if any) leaving node j, then these two arcs contribute to the total changeover cost of T by the quantity dab, a non-negative entry of a k-dimensional square matrix D. We first prove that the problem is NPO-complete and very hard to approximate. Then we present a greedy heuristic together with combinatorial lower and upper bounds, a Binary Quadratic Programming formulation, and exact solution approaches based on branch-and-cut solvers. Finally, we report extensive computational results and exhibit a set of very challenging instances.

## Citation

Conference version of this paper, please cite: G. Galbiati, S. Gualandi, F. Maffioli. On Minimum Changeover Cost Arborescences. In Proc. of International Symposium on Experimental Algorithms (SEA), LNCS 6630, pp 112-123, 2011. DOI: 10.1007/978-3-642-20662-7_10

## Article

View Complexity and Exact Solution Approaches to the Minimum Changeover Cost Arborescence Problem