# is.multiple

##### Find the multiple or loop edges in a graph

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.

- Keywords
- graphs

##### Usage

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

##### Arguments

- graph
- The input graph.
- eids
- The edges to which the query is restricted. By default this is all edges in the graph.

##### 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

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.

##### concept

Simple graph

##### 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
```

*Documentation reproduced from package igraph, version 0.6.5-2, License: GPL (>= 2)*