# edges2vees: List Dihedral Triples in a Graph

## Description

Given a list of edges between vertices,
compile a list of all ‘vees’ or dihedral triples
formed by these edges.

## Usage

edges2vees(iedge, jedge, nvert=max(iedge, jedge), …,
check=TRUE)

## Arguments

iedge,jedge

Integer vectors, of equal length, specifying the edges.

nvert

Number of vertices in the network.

check

Logical. Whether to check validity of input data.

## Value

A 3-column matrix of integers, in which each row represents a triple
of vertices, with the first vertex joined to the other two vertices.

## Details

Given a finite graph with `nvert`

vertices and with edges
specified by `iedge, jedge`

, this low-level function
finds all ‘vees’ or ‘dihedral triples’
in the graph, that is, all triples
of vertices `(i,j,k)`

where `i`

and `j`

are joined by
an edge and `i`

and `k`

are joined by an edge.

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`

.

## Examples

# NOT RUN {
i <- c(1, 2, 5, 5, 1, 4, 2)
j <- c(2, 3, 3, 1, 3, 2, 5)
edges2vees(i, j)
# }