spatstat (version 1.64-1)

# edges2triangles: List Triangles in a Graph

## Description

Given a list of edges between vertices, compile a list of all triangles formed by these edges.

## Usage

```edges2triangles(iedge, jedge, nvert=max(iedge, jedge), …,
check=TRUE, friendly=rep(TRUE, nvert))```

## Arguments

iedge,jedge

Integer vectors, of equal length, specifying the edges.

nvert

Number of vertices in the network.

Ignored

check

Logical. Whether to check validity of input data.

friendly

Optional. For advanced use. See Details.

## Value

A 3-column matrix of integers, in which each row represents a triangle.

## Details

This low level function finds all the triangles (cliques of size 3) in a finite graph with `nvert` vertices and with edges specified by `iedge, jedge`.

The interpretation of `iedge, jedge` is that each successive pair of entries specifies an edge in the graph. The \(k\)th edge joins vertex `iedge[k]` to vertex `jedge[k]`. Entries of `iedge` and `jedge` must be integers from 1 to `nvert`.

To improve efficiency in some applications, the optional argument `friendly` can be used. It should be a logical vector of length `nvert` specifying a labelling of the vertices, such that two vertices `j,k` which are not friendly (`friendly[j] = friendly[k] = FALSE`) are never connected by an edge.

`edges2vees`

## Examples

Run this code
``````# NOT RUN {
i <- c(1, 2, 5, 5, 1, 4, 2)
j <- c(2, 3, 3, 1, 3, 2, 5)
edges2triangles(i, j)
# }
``````

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