spatstat.geom (version 3.3-2)

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))

Value

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

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.

Author

Adrian Baddeley

and Rolf Turner

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.

See Also

edges2vees

Examples

 i <- c(1, 2, 5, 5, 1, 4, 2)
 j <- c(2, 3, 3, 1, 3, 2, 5)
 edges2triangles(i, j)