Aaron Archer Ranjithkumar Rajagopalan David B. Shmoys Lagrangian Relaxation for the k-Median Problem: New Insights and Continuity Properties. 31-42 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2832&spage=31 2003 conf/esa/2003 ESA db/conf/esa/esa2003.html#ArcherRS03