Dan Feldman Amos Fiat Micha Sharir Danny Segev Bi-criteria linear-time approximations for generalized k-mean/median/center. 19-26 2007 conf/compgeom/2007 Symposium on Computational Geometry http://doi.acm.org/10.1145/1247069.1247073 db/conf/compgeom/compgeom2007.html#FeldmanFSS07