Ehab Morsy Hiroshi Nagamochi Approximation Algorithms for Multicast Routings in a Network with Multi-Sources. 900-906 2007 90-A IEICE Transactions 5 http://dx.doi.org/10.1093/ietfec/e90-a.5.900 db/journals/ieicet/ieicet90a.html#MorsyN07