The mixed center location problem

This paper studies a new version of the location problem called the mixedcenterlocation problem. Let P be a set of n points in the plane. We first consider the mixed 2-center problem, where one of the centers must be in P, and we solve it in O(n²log n) time. Second, we consider the mixed k-center problem, where m of the centers are in P, and we solve it in O(nm+O(k-m)) time. Motivated by two practical constraints, we propose two variations of the problem. Third, we present a 2-approximation algorithm and three heuristics solving the mixed k-center problem (k> 2).