This function checks the reciprocal pair of the supplied edges.

## Usage

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

## Arguments

- graph
The input graph.

- eids
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.

## See also

`reciprocity()`

, `dyad_census()`

if you just
want some statistics about mutual edges.

Other structural.properties:
`bfs()`

,
`component_distribution()`

,
`connect()`

,
`constraint()`

,
`coreness()`

,
`degree()`

,
`dfs()`

,
`distance_table()`

,
`edge_density()`

,
`feedback_arc_set()`

,
`girth()`

,
`is_acyclic()`

,
`is_dag()`

,
`is_matching()`

,
`knn()`

,
`laplacian_matrix()`

,
`reciprocity()`

,
`subcomponent()`

,
`subgraph()`

,
`topo_sort()`

,
`transitivity()`

,
`unfold_tree()`

,
`which_multiple()`

## Author

Gabor Csardi csardi.gabor@gmail.com

## Examples

```
g <- sample_gnm(10, 50, directed = TRUE)
reciprocity(g)
#> [1] 0.6
dyad_census(g)
#> $mut
#> [1] 15
#>
#> $asym
#> [1] 20
#>
#> $null
#> [1] 10
#>
which_mutual(g)
#> [1] TRUE FALSE TRUE TRUE TRUE FALSE TRUE TRUE FALSE FALSE FALSE TRUE
#> [13] TRUE FALSE FALSE TRUE TRUE FALSE TRUE TRUE FALSE TRUE TRUE TRUE
#> [25] TRUE FALSE TRUE FALSE FALSE FALSE TRUE TRUE FALSE TRUE TRUE FALSE
#> [37] TRUE TRUE TRUE TRUE TRUE TRUE FALSE TRUE TRUE FALSE TRUE FALSE
#> [49] FALSE FALSE
sum(which_mutual(g)) / 2 == dyad_census(g)$mut
#> [1] TRUE
```