Find the multiple or loop edges in a graph

Description

A loop edge is an edge from a vertex to itself. An edge is a multiple edge if it has exactly the same head and tail vertices as another edge. A graph without multiple and loop edges is called a simple graph.

Usage

is.loop(graph, eids=E(graph))
has.multiple(graph)
is.multiple(graph, eids=E(graph))
count.multiple(graph, eids=E(graph))

Arguments

Details

is.loop decides whether the edges of the graph are loop edges.

has.multiple decides whether the graph has any multiple edges.

is.multiple decides whether the edges of the graph are multiple edges.

count.multiple counts the multiplicity of each edge of a graph.

Note that the semantics for is.multiple and count.multiple is different. is.multiple gives TRUE for all occurences of a multiple edge except for one. Ie. if there are three i-j edges in the graph then is.multiple returns TRUE for only two of them while count.multiple returns ‘3’ for all three.

See the examples for getting rid of multiple edges while keeping their original multiplicity as an edge attribute.

Value

has.multiple returns a logical scalar. is.loop and is.multiple return a logical vector. count.multiple returns a numeric vector.

Author(s)

Gabor Csardi csardi.gabor@gmail.com

See Also

simplify to eliminate loop and multiple edges.

Examples

# Loops
g <- graph( c(1,1,2,2,3,3,4,5) )
is.loop(g)

# Multiple edges
g <- barabasi.game(10, m=3, algorithm="bag")
has.multiple(g)
is.multiple(g)
count.multiple(g)
is.multiple(simplify(g))
all(count.multiple(simplify(g)) == 1)

# Direction of the edge is important
is.multiple(graph( c(1,2, 2,1) ))
is.multiple(graph( c(1,2, 2,1), dir=FALSE ))

# Remove multiple edges but keep multiplicity
g <- barabasi.game(10, m=3, algorithm="bag")
E(g)$weight <- count.multiple(g)
g <- simplify(g)
any(is.multiple(g))
E(g)$weight