The diameter of a graph is the length of the longest geodesic.

## Usage

```
diameter(graph, directed = TRUE, unconnected = TRUE, weights = NULL)
get_diameter(graph, directed = TRUE, unconnected = TRUE, weights = NULL)
farthest_vertices(graph, directed = TRUE, unconnected = TRUE, weights = NULL)
```

## Arguments

- graph
The graph to analyze.

- directed
Logical, whether directed or undirected paths are to be considered. This is ignored for undirected graphs.

- unconnected
Logical, what to do if the graph is unconnected. If FALSE, the function will return a number that is one larger the largest possible diameter, which is always the number of vertices. If TRUE, the diameters of the connected components will be calculated and the largest one will be returned.

- weights
Optional positive weight vector for calculating weighted distances. If the graph has a

`weight`

edge attribute, then this is used by default.

## Value

A numeric constant for `diameter()`

, a numeric vector for
`get_diameter()`

. `farthest_vertices()`

returns a list with two
entries:

`vertices`

The two vertices that are the farthest.`distance`

Their distance.

## Details

The diameter is calculated by using a breadth-first search like method.

`get_diameter()`

returns a path with the actual diameter. If there are
many shortest paths of the length of the diameter, then it returns the first
one found.

`farthest_vertices()`

returns two vertex ids, the vertices which are
connected by the diameter path.

## See also

Other paths:
`all_simple_paths()`

,
`distance_table()`

,
`eccentricity()`

,
`graph_center()`

,
`radius()`

## Author

Gabor Csardi csardi.gabor@gmail.com

## Examples

```
g <- make_ring(10)
g2 <- delete_edges(g, c(1, 2, 1, 10))
diameter(g2, unconnected = TRUE)
#> [1] 7
diameter(g2, unconnected = FALSE)
#> [1] Inf
## Weighted diameter
set.seed(1)
g <- make_ring(10)
E(g)$weight <- sample(seq_len(ecount(g)))
diameter(g)
#> [1] 27
get_diameter(g)
#> + 5/10 vertices, from 38d7ccd:
#> [1] 1 10 9 8 7
diameter(g, weights = NA)
#> [1] 5
get_diameter(g, weights = NA)
#> + 6/10 vertices, from 38d7ccd:
#> [1] 1 2 3 4 5 6
```