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NAME
digraph - Directed Graphs
DESCRIPTION
The digraph module implements a version of labeled directed graphs. What makes the graphs implemented
here non-proper directed graphs is that multiple edges between vertices are allowed. However, the
customary definition of directed graphs will be used in the text that follows.
A directed graph (or just "digraph") is a pair (V, E) of a finite set V of vertices and a finite set E of
directed edges (or just "edges"). The set of edges E is a subset of V x V (the Cartesian product of V
with itself). In this module, V is allowed to be empty; the so obtained unique digraph is called the
empty digraph. Both vertices and edges are represented by unique Erlang terms.
Digraphs can be annotated with additional information. Such information may be attached to the vertices
and to the edges of the digraph. A digraph which has been annotated is called a labeled digraph, and the
information attached to a vertex or an edge is called a label. Labels are Erlang terms.
An edge e = (v, w) is said to emanate from vertex v and to be incident on vertex w. The out-degree of a
vertex is the number of edges emanating from that vertex. The in-degree of a vertex is the number of
edges incident on that vertex. If there is an edge emanating from v and incident on w, then w is said to
be an out-neighbour of v, and v is said to be an in-neighbour of w. A path P from v[1] to v[k] in a
digraph (V, E) is a non-empty sequence v[1], v[2], ..., v[k] of vertices in V such that there is an edge
(v[i],v[i+1]) in E for 1 <= i < k. The length of the path P is k-1. P is simple if all vertices are
distinct, except that the first and the last vertices may be the same. P is a cycle if the length of P is
not zero and v[1] = v[k]. A loop is a cycle of length one. A simple cycle is a path that is both a cycle
and simple. An acyclic digraph is a digraph that has no cycles.
DATA TYPES
d_type() = d_cyclicity() | d_protection()
d_cyclicity() = acyclic | cyclic
d_protection() = private | protected
digraph()
A digraph as returned by new/0,1.
edge()
label() = term()
vertex()
EXPORTS
add_edge(G, V1, V2) -> edge() | {error, add_edge_err_rsn()}
add_edge(G, V1, V2, Label) -> edge() | {error, add_edge_err_rsn()}
add_edge(G, E, V1, V2, Label) ->
edge() | {error, add_edge_err_rsn()}
Types:
G = digraph()
E = edge()
V1 = V2 = vertex()
Label = label()
add_edge_err_rsn() = {bad_edge, Path :: [vertex()]}
| {bad_vertex, V :: vertex()}
add_edge/5 creates (or modifies) the edge E of the digraph G, using Label as the (new) label of
the edge. The edge is emanating from V1 and incident on V2. Returns E.
add_edge(G, V1, V2, Label) is equivalent to add_edge(G, E, V1, V2, Label), where E is a created
edge. The created edge is represented by the term ['$e' | N], where N is an integer >= 0.
add_edge(G, V1, V2) is equivalent to add_edge(G, V1, V2, []).
If the edge would create a cycle in an acyclic digraph, then {error, {bad_edge, Path}} is
returned. If either of V1 or V2 is not a vertex of the digraph G, then {error, {bad_vertex, V}} is
returned, V = V1 or V = V2.
add_vertex(G) -> vertex()
add_vertex(G, V) -> vertex()
add_vertex(G, V, Label) -> vertex()
Types:
G = digraph()
V = vertex()
Label = label()
add_vertex/3 creates (or modifies) the vertex V of the digraph G, using Label as the (new) label
of the vertex. Returns V.
add_vertex(G, V) is equivalent to add_vertex(G, V, []).
add_vertex/1 creates a vertex using the empty list as label, and returns the created vertex. The
created vertex is represented by the term ['$v' | N], where N is an integer >= 0.
del_edge(G, E) -> true
Types:
G = digraph()
E = edge()
Deletes the edge E from the digraph G.
del_edges(G, Edges) -> true
Types:
G = digraph()
Edges = [edge()]
Deletes the edges in the list Edges from the digraph G.
del_path(G, V1, V2) -> true
Types:
G = digraph()
V1 = V2 = vertex()
Deletes edges from the digraph G until there are no paths from the vertex V1 to the vertex V2.
A sketch of the procedure employed: Find an arbitrary simple path v[1], v[2], ..., v[k] from V1 to
V2 in G. Remove all edges of G emanating from v[i] and incident to v[i+1] for 1 <= i < k
(including multiple edges). Repeat until there is no path between V1 and V2.
del_vertex(G, V) -> true
Types:
G = digraph()
V = vertex()
Deletes the vertex V from the digraph G. Any edges emanating from V or incident on V are also
deleted.
del_vertices(G, Vertices) -> true
Types:
G = digraph()
Vertices = [vertex()]
Deletes the vertices in the list Vertices from the digraph G.
delete(G) -> true
Types:
G = digraph()
Deletes the digraph G. This call is important because digraphs are implemented with ETS. There is
no garbage collection of ETS tables. The digraph will, however, be deleted if the process that
created the digraph terminates.
edge(G, E) -> {E, V1, V2, Label} | false
Types:
G = digraph()
E = edge()
V1 = V2 = vertex()
Label = label()
Returns {E, V1, V2, Label} where Label is the label of the edge E emanating from V1 and incident
on V2 of the digraph G. If there is no edge E of the digraph G, then false is returned.
edges(G) -> Edges
Types:
G = digraph()
Edges = [edge()]
Returns a list of all edges of the digraph G, in some unspecified order.
edges(G, V) -> Edges
Types:
G = digraph()
V = vertex()
Edges = [edge()]
Returns a list of all edges emanating from or incident on V of the digraph G, in some unspecified
order.
get_cycle(G, V) -> Vertices | false
Types:
G = digraph()
V = vertex()
Vertices = [vertex(), ...]
If there is a simple cycle of length two or more through the vertex V, then the cycle is returned
as a list [V, ..., V] of vertices, otherwise if there is a loop through V, then the loop is
returned as a list [V]. If there are no cycles through V, then false is returned.
get_path/3 is used for finding a simple cycle through V.
get_path(G, V1, V2) -> Vertices | false
Types:
G = digraph()
V1 = V2 = vertex()
Vertices = [vertex(), ...]
Tries to find a simple path from the vertex V1 to the vertex V2 of the digraph G. Returns the path
as a list [V1, ..., V2] of vertices, or false if no simple path from V1 to V2 of length one or
more exists.
The digraph G is traversed in a depth-first manner, and the first path found is returned.
get_short_cycle(G, V) -> Vertices | false
Types:
G = digraph()
V = vertex()
Vertices = [vertex(), ...]
Tries to find an as short as possible simple cycle through the vertex V of the digraph G. Returns
the cycle as a list [V, ..., V] of vertices, or false if no simple cycle through V exists. Note
that a loop through V is returned as the list [V, V].
get_short_path/3 is used for finding a simple cycle through V.
get_short_path(G, V1, V2) -> Vertices | false
Types:
G = digraph()
V1 = V2 = vertex()
Vertices = [vertex(), ...]
Tries to find an as short as possible simple path from the vertex V1 to the vertex V2 of the
digraph G. Returns the path as a list [V1, ..., V2] of vertices, or false if no simple path from
V1 to V2 of length one or more exists.
The digraph G is traversed in a breadth-first manner, and the first path found is returned.
in_degree(G, V) -> integer() >= 0
Types:
G = digraph()
V = vertex()
Returns the in-degree of the vertex V of the digraph G.
in_edges(G, V) -> Edges
Types:
G = digraph()
V = vertex()
Edges = [edge()]
Returns a list of all edges incident on V of the digraph G, in some unspecified order.
in_neighbours(G, V) -> Vertex
Types:
G = digraph()
V = vertex()
Vertex = [vertex()]
Returns a list of all in-neighbours of V of the digraph G, in some unspecified order.
info(G) -> InfoList
Types:
G = digraph()
InfoList =
[{cyclicity, Cyclicity :: d_cyclicity()} |
{memory, NoWords :: integer() >= 0} |
{protection, Protection :: d_protection()}]
d_cyclicity() = acyclic | cyclic
d_protection() = private | protected
Returns a list of {Tag, Value} pairs describing the digraph G. The following pairs are returned:
* {cyclicity, Cyclicity}, where Cyclicity is cyclic or acyclic, according to the options given
to new.
* {memory, NoWords}, where NoWords is the number of words allocated to the ETS tables.
* {protection, Protection}, where Protection is protected or private, according to the options
given to new.
new() -> digraph()
Equivalent to new([]).
new(Type) -> digraph()
Types:
Type = [d_type()]
d_type() = d_cyclicity() | d_protection()
d_cyclicity() = acyclic | cyclic
d_protection() = private | protected
Returns an empty digraph with properties according to the options in Type:
cyclic:
Allow cycles in the digraph (default).
acyclic:
The digraph is to be kept acyclic.
protected:
Other processes can read the digraph (default).
private:
The digraph can be read and modified by the creating process only.
If an unrecognized type option T is given or Type is not a proper list, there will be a badarg
exception.
no_edges(G) -> integer() >= 0
Types:
G = digraph()
Returns the number of edges of the digraph G.
no_vertices(G) -> integer() >= 0
Types:
G = digraph()
Returns the number of vertices of the digraph G.
out_degree(G, V) -> integer() >= 0
Types:
G = digraph()
V = vertex()
Returns the out-degree of the vertex V of the digraph G.
out_edges(G, V) -> Edges
Types:
G = digraph()
V = vertex()
Edges = [edge()]
Returns a list of all edges emanating from V of the digraph G, in some unspecified order.
out_neighbours(G, V) -> Vertices
Types:
G = digraph()
V = vertex()
Vertices = [vertex()]
Returns a list of all out-neighbours of V of the digraph G, in some unspecified order.
vertex(G, V) -> {V, Label} | false
Types:
G = digraph()
V = vertex()
Label = label()
Returns {V, Label} where Label is the label of the vertex V of the digraph G, or false if there is
no vertex V of the digraph G.
vertices(G) -> Vertices
Types:
G = digraph()
Vertices = [vertex()]
Returns a list of all vertices of the digraph G, in some unspecified order.
SEE ALSO
digraph_utils(3erl), ets(3erl)