1. Aardal, K.I., Chudak, F.A., Shmoys, D.B.: A 3-approximation algorithm for the $$k$$-level uncapacitated facility location problem. Inf. Process. Lett. 72, 161–167 (1999)
2. Arya, V., Garg, N., Khandekar, R., Meyerson, A., Munagala, K., Pandit, V.: Local search heuristics for $$k$$-median and facility location problems. SIAM J. Comput. 33, 544–562 (2004)
3. Asadi, M., Niknafs, A., Ghodsi, M.: An approximation algorithm for the $$k$$-level uncapacitated facility location problem with penalties. In: Proceedings of the 13th International Computer Society of Iran Computer Conference on Advances in Computer Science and Engineering, pp. 41–49 (2008)
4. Bumb, A., Kern, W.: A simple dual ascent algorithm for the multilevel facility location problem. In: Proceedings of the 4th International Workshop on Approximation Algorithms for Combinatorial Optimization, pp. 55–62 (2001)
5. Bumb, A.: Approximation Algorithms for Facility Location Problem. Ph.D. Thesis, University of Twente (2002)