digraph(3erl)
NAME
digraph - Directed graphs.
DESCRIPTION
This module provides a version of labeled directed graphs. What makes
the graphs provided here non-proper directed graphs is that multiple
edges between vertices are allowed. However, the customary definition
of directed graphs is used here.
* 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 more information. Such information
can be attached to the vertices and to the edges of the digraph. An
annotated digraph 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 an edge is emanating from v and incident on w, then w is said to
be an out-neighbor of v, and v is said to be an in-neighbor 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 path P is k-1.
* Path P is simple if all vertices are distinct, except that the
first and the last vertices can be the same.
* Path 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 without cycles.
DATA TYPES
d_type() = d_cyclicity() | d_protection()
d_cyclicity() = acyclic | cyclic
d_protection() = private | protected
graph()
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 = graph()
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) edge E of 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 term ['$e' | N], where N is an integer >= 0.
add_edge(G, V1, V2) is equivalent to add_edge(G, V1, V2, []).
If the edge would create a cycle in an acyclic digraph, {error,
{bad_edge, Path}} is returned. If either of V1 or V2 is not a
vertex of digraph G, {error, {bad_vertex, V}} is returned, V =
V1 or V = V2.
add_vertex(G) -> vertex()
add_vertex(G, V) -> vertex()
add_vertex(G, V, Label) -> vertex()
Types:
G = graph()
V = vertex()
Label = label()
add_vertex/3 creates (or modifies) vertex V of digraph G, using
Label as the (new) label of the vertex. Returns V.
add_vertex(G, V) is equivalent to add_vertex(G, V, []).
add_vertex/1 creates a vertex using the empty list as label, and
returns the created vertex. The created vertex is represented by
term ['$v' | N], where N is an integer >= 0.
del_edge(G, E) -> true
Types:
G = graph()
E = edge()
Deletes edge E from digraph G.
del_edges(G, Edges) -> true
Types:
G = graph()
Edges = [edge()]
Deletes the edges in list Edges from digraph G.
del_path(G, V1, V2) -> true
Types:
G = graph()
V1 = V2 = vertex()
Deletes edges from digraph G until there are no paths from
vertex V1 to 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 = graph()
V = vertex()
Deletes vertex V from digraph G. Any edges emanating from V or
incident on V are also deleted.
del_vertices(G, Vertices) -> true
Types:
G = graph()
Vertices = [vertex()]
Deletes the vertices in list Vertices from digraph G.
delete(G) -> true
Types:
G = graph()
Deletes digraph G. This call is important as digraphs are
implemented with ETS. There is no garbage collection of ETS
tables. However, the digraph is deleted if the process that
created the digraph terminates.
edge(G, E) -> {E, V1, V2, Label} | false
Types:
G = graph()
E = edge()
V1 = V2 = vertex()
Label = label()
Returns {E, V1, V2, Label}, where Label is the label of edge E
emanating from V1 and incident on V2 of digraph G. If no edge E
of digraph G exists, false is returned.
edges(G) -> Edges
Types:
G = graph()
Edges = [edge()]
Returns a list of all edges of digraph G, in some unspecified
order.
edges(G, V) -> Edges
Types:
G = graph()
V = vertex()
Edges = [edge()]
Returns a list of all edges emanating from or incident onV of
digraph G, in some unspecified order.
get_cycle(G, V) -> Vertices | false
Types:
G = graph()
V = vertex()
Vertices = [vertex(), ...]
If a simple cycle of length two or more exists through vertex V,
the cycle is returned as a list [V, ..., V] of vertices. If a
loop through V exists, the loop is returned as a list [V]. If no
cycles through V exist, false is returned.
get_path/3 is used for finding a simple cycle through V.
get_path(G, V1, V2) -> Vertices | false
Types:
G = graph()
V1 = V2 = vertex()
Vertices = [vertex(), ...]
Tries to find a simple path from vertex V1 to vertex V2 of
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.
Digraph G is traversed in a depth-first manner, and the first
found path is returned.
get_short_cycle(G, V) -> Vertices | false
Types:
G = graph()
V = vertex()
Vertices = [vertex(), ...]
Tries to find an as short as possible simple cycle through
vertex V of digraph G. Returns the cycle as a list [V, ..., V]
of vertices, or false if no simple cycle through V exists.
Notice that a loop through V is returned as 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 = graph()
V1 = V2 = vertex()
Vertices = [vertex(), ...]
Tries to find an as short as possible simple path from vertex V1
to vertex V2 of 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.
Digraph G is traversed in a breadth-first manner, and the first
found path is returned.
in_degree(G, V) -> integer() >= 0
Types:
G = graph()
V = vertex()
Returns the in-degree of vertex V of digraph G.
in_edges(G, V) -> Edges
Types:
G = graph()
V = vertex()
Edges = [edge()]
Returns a list of all edges incident on V of digraph G, in some
unspecified order.
in_neighbours(G, V) -> Vertex
Types:
G = graph()
V = vertex()
Vertex = [vertex()]
Returns a list of all in-neighbors of V of digraph G, in some
unspecified order.
info(G) -> InfoList
Types:
G = graph()
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 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() -> graph()
Equivalent to new([]).
new(Type) -> graph()
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:
Allows 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 specified or Type is not a
proper list, a badarg exception is raised.
no_edges(G) -> integer() >= 0
Types:
G = graph()
Returns the number of edges of digraph G.
no_vertices(G) -> integer() >= 0
Types:
G = graph()
Returns the number of vertices of digraph G.
out_degree(G, V) -> integer() >= 0
Types:
G = graph()
V = vertex()
Returns the out-degree of vertex V of digraph G.
out_edges(G, V) -> Edges
Types:
G = graph()
V = vertex()
Edges = [edge()]
Returns a list of all edges emanating from V of digraph G, in
some unspecified order.
out_neighbours(G, V) -> Vertices
Types:
G = graph()
V = vertex()
Vertices = [vertex()]
Returns a list of all out-neighbors of V of digraph G, in some
unspecified order.
vertex(G, V) -> {V, Label} | false
Types:
G = graph()
V = vertex()
Label = label()
Returns {V, Label}, where Label is the label of the vertex V of
digraph G, or false if no vertex V of digraph G exists.
vertices(G) -> Vertices
Types:
G = graph()
Vertices = [vertex()]
Returns a list of all vertices of digraph G, in some unspecified
order.
SEE ALSO
digraph_utils(3erl), ets(3erl)
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