سلام دوستان عزیز.مقاله زیر رو لطف کنید.مرسی
A series of approximation algorithms for the acyclic directed steiner tree problem
JournalAlgorithmica
PublisherSpringer New YorkISSN0178-4617 (Print) 1432-0541 (Online)Issue
Volume 18, Number 1 / May, 1997
DOI10.1007/BF02523690...