Www.cmap.polytechnique.fr/~elkaroui/masterfin034.pdf. Graph (mathematics) The edges may be directed or undirected.
For example, if the vertices represent people at a party, and there is an edge between two people if they shake hands, then this is an undirected graph, because if person A shook hands with person B, then person B also shook hands with person A. In contrast, if there is an edge from person A to person B when person A knows of person B, then this graph is directed, because knowledge of someone is not necessarily a symmetric relation (that is, one person knowing another person does not necessarily imply the reverse; for example, many fans may know of a celebrity, but the celebrity is unlikely to know of all their fans).
This latter type of graph is called a directed graph and the edges are called directed edges or arcs.
Algèbre. Computational Game Theory. Probabilités. Géométrie. Analyse. Statistiques. Abramowitz and Stegun: Handbook of Mathematical Functions.