# is.multiple

From igraph v0.5.5-3
by Gabor Csardi

##### 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))
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

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

`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(0,0,1,1,2,2,3,4) )
is.loop(g)
# Multiple edges
g <- barabasi.game(10, m=3)
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(0,1, 1,0) ))
is.multiple(graph( c(0,1, 1,0), dir=FALSE ))
# Remove multiple edges but keep multiplicity
g <- barabasi.game(10, m=3)
E(g)$weight <- count.multiple(g)
g <- simplify(g)
any(is.multiple(g))
E(g)$weight
```

*Documentation reproduced from package igraph, version 0.5.5-3, License: GPL (>= 2)*

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