# which_mutual

From igraph v1.2.3
by Gabor Csardi

##### Find mutual edges in a directed graph

This function checks the reciproc pair of the supplied edges.

- Keywords
- graphs

##### Usage

`which_mutual(graph, es = E(graph))`

##### Arguments

- graph
The input graph.

- es
Edge sequence, the edges that will be probed. By default is includes all edges in the order of their ids.

##### Details

In a directed graph an (A,B) edge is mutual if the graph also includes a (B,A) directed edge.

Note that multi-graphs are not handled properly, i.e. if the graph contains two copies of (A,B) and one copy of (B,A), then these three edges are considered to be mutual.

Undirected graphs contain only mutual edges by definition.

##### Value

A logical vector of the same length as the number of edges supplied.

##### See Also

`reciprocity`

, `dyad_census`

if you just
want some statistics about mutual edges.

##### Examples

```
# NOT RUN {
g <- sample_gnm(10, 50, directed=TRUE)
reciprocity(g)
dyad_census(g)
which_mutual(g)
sum(which_mutual(g))/2 == dyad_census(g)$mut
# }
```

*Documentation reproduced from package igraph, version 1.2.3, License: GPL (>= 2)*

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