Chandra Chekuri Rajeev Motwani B. Natarajan Clifford Stein Approximation Techniques for Average Completion Time Scheduling. 146-166 2001 31 SIAM J. Comput. 1 http://epubs.siam.org/sam-bin/dbq/article/32718 db/journals/siamcomp/siamcomp31.html#ChekuriMNS01