Isa Nakhai Kamalabadi Seyed Hessameddin Zegordi Ali Hossein Mirzaei Developing an improved particle swarm optimization algorithm for solving the inventory routing problem with direct shipment. 221-225 2011 IEEM http://dx.doi.org/10.1109/IEEM.2011.6117911 conf/ieem/2011 db/conf/ieem/ieem2011.html#KamalabadiZM11