is_forest()
decides whether a graph is a forest, and optionally returns a
set of possible root vertices for its components.
Usage
is_forest(graph, mode = c("out", "in", "all", "total"), details = FALSE)
Arguments
- graph
An igraph graph object
- mode
Whether to consider edge directions in a directed graph. ‘all’ ignores edge directions; ‘out’ requires edges to be oriented outwards from the root, ‘in’ requires edges to be oriented towards the root.
- details
Whether to return only whether the graph is a tree (
FALSE
) or also a possible root (TRUE
)
Value
When details
is FALSE
, a logical value that indicates
whether the graph is a tree. When details
is TRUE
, a named
list with two entries:
- res
Logical value that indicates whether the graph is a tree.
- root
The root vertex of the tree; undefined if the graph is not a tree.
Details
An undirected graph is a forest if it has no cycles. In the directed case, a possible additional requirement is that edges in each tree are oriented away from the root (out-trees or arborescences) or all edges are oriented towards the root (in-trees or anti-arborescences). This test can be controlled using the mode parameter.
By convention, the null graph (i.e. the graph with no vertices) is considered to be a forest.
See also
Other trees:
is_tree()
,
make_from_prufer()
,
sample_spanning_tree()
,
to_prufer()