# count_triangles

From igraph v1.2.3
by Gabor Csardi

##### Find triangles in graphs

Count how many triangles a vertex is part of, in a graph, or just list the triangles of a graph.

- Keywords
- graphs

##### Usage

`count_triangles(graph, vids = V(graph))`

##### Arguments

- graph
The input graph. It might be directed, but edge directions are ignored.

- vids
The vertices to query, all of them by default. This might be a vector of numeric ids, or a character vector of symbolic vertex names for named graphs.

##### Details

`triangles`

lists all triangles of a graph. For efficiency, all
triangles are returned in a single vector. The first three vertices belong
to the first triangle, etc.

`count_triangles`

counts how many triangles a vertex is part of.

##### Value

For `triangles`

a numeric vector of vertex ids, the first three
vertices belong to the first triangle found, etc.

For `count_triangles`

a numeric vector, the number of triangles for all
vertices queried.

##### See Also

##### Examples

```
# NOT RUN {
## A small graph
kite <- make_graph("Krackhardt_Kite")
plot(kite)
matrix(triangles(kite), nrow=3)
## Adjacenct triangles
atri <- count_triangles(kite)
plot(kite, vertex.label=atri)
## Always true
sum(count_triangles(kite)) == length(triangles(kite))
## Should match, local transitivity is the
## number of adjacent triangles divided by the number
## of adjacency triples
transitivity(kite, type="local")
count_triangles(kite) / (degree(kite) * (degree(kite)-1)/2)
# }
```

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

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