 Second, when analyzing directed networks, people often treat them as undirected ones for simplicity; therefore, the information obtained from reciprocity studies helps to estimate the error introduced when a directed network is treated as undirected (for example, when measuring the clustering coefficient).Finally, detecting nontrivial patterns of reciprocity can reveal possible mechanisms and organizing principles that shape the observed network's topology.A traditional way to define the reciprocity r is using the ratio of the number of links pointing in both directions formula_1 to the total number of links L 
formula_2

With this definition, formula_3 is for a purely bidirectional network while
formula_4 for a purely unidirectional one.