A local source is a node of a directed graph with no entering edges (Borowski and Borwein 1991, p. 401; left figure), and a global source (often simply called a source) is a node in a directed graph which reaches all other nodes (Harary 1994, p. 201; right figure).
Digraph Source
See also
Digraph Sink, Directed Graph, NetworkExplore with Wolfram|Alpha
References
Borowski, E. J. and Borwein, J. M. (Eds.). The HarperCollins Dictionary of Mathematics. New York: HarperCollins, 1991.Harary, F. Graph Theory. Reading, MA: Addison-Wesley, 1994.Cite this as:
Weisstein, Eric W. "Digraph Source." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/DigraphSource.html