Provided by: libgraph-perl_0.96-1.1_all 
NAME
Graph - graph data structures and algorithms
SYNOPSIS
use Graph;
my $g0 = Graph->new; # A directed graph.
use Graph::Directed;
my $g1 = Graph::Directed->new; # A directed graph.
use Graph::Undirected;
my $g2 = Graph::Undirected->new; # An undirected graph.
$g->add_edge(...);
$g->has_edge(...)
$g->delete_edge(...);
$g->add_vertex(...);
$g->has_vertex(...);
$g->delete_vertex(...);
$g->vertices(...)
$g->edges(...)
# And many, many more, see below.
UNSUPPORTED
Unfortunately, as of release 0.95, this module is unsupported, and will no more be
maintained. Sorry about that.
DESCRIPTION
Non-Description
This module is not for drawing or rendering any sort of graphics or images, business,
visualization, or otherwise.
Description
Instead, this module is for creating abstract data structures called graphs, and for doing
various operations on those.
Perl 5.6.0 minimum
The implementation depends on a Perl feature called "weak references" and Perl 5.6.0 was
the first to have those.
Constructors
new Create an empty graph.
Graph->new(%options)
The options are a hash with option names as the hash keys and the option values as the
hash values.
The following options are available:
directed
A boolean option telling that a directed graph should be created. Often
somewhat redundant because a directed graph is the default for the Graph class
or one could simply use the "new()" constructor of the Graph::Directed class.
You can test the directness of a graph with $g->is_directed() and
$g->is_undirected().
undirected
A boolean option telling that an undirected graph should be created. One
could also use the "new()" constructor the Graph::Undirected class instead.
Note that while often it is possible to think undirected graphs as
bidirectional graphs, or as directed graphs with edges going both ways, in
this module directed graphs and undirected graphs are two different things
that often behave differently.
You can test the directness of a graph with $g->is_directed() and
$g->is_undirected().
refvertexed
refvertexed_stringified
If you want to use references (including Perl objects) as vertices, use
"refvertexed".
Note that using "refvertexed" means that internally the memory address of the
reference (for example, a Perl object) is used as the "identifier" of the
vertex, not the stringified form of the reference, even if you have defined
your own stringification using "overload".
This avoids the problem of the stringified references potentially being
identical (because they are identical in value, for example) even if the
references are different. If you really want to use references and their
stringified forms as the identities, use the "refvertexed_stringified". But
please do not stringify different objects to the same stringified value.
unionfind
If the graph is undirected, you can specify the "unionfind" parameter to use
the so-called union-find scheme to speed up the computation of connected
components of the graph (see "is_connected", "connected_components",
"connected_component_by_vertex", "connected_component_by_index", and
"same_connected_components"). If "unionfind" is used, adding edges (and
vertices) becomes slower, but connectedness queries become faster. You must
not delete egdes or vertices of an unionfind graph, only add them. You can
test a graph for "union-findness" with
has_union_find
Returns true if the graph was created with a true "unionfind" parameter.
vertices
An array reference of vertices to add.
edges An array reference of array references of edge vertices to add.
copy
copy_graph
my $c = $g->copy_graph;
Create a shallow copy of the structure (vertices and edges) of the graph. If you want
a deep copy that includes attributes, see "deep_copy". The copy will have the same
directedness as the original, and if the original was a "compat02" graph, the copy
will be, too.
Also the following vertex/edge attributes are copied:
refvertexed/hypervertexed/countvertexed/multivertexed
hyperedged/countedged/multiedged/omniedged
deep_copy
deep_copy_graph
my $c = $g->deep_copy_graph;
Create a deep copy of the graph (vertices, edges, and attributes) of the graph. If
you want a shallow copy that does not include attributes, see "copy".
Note that copying code references only works with Perls 5.8 or later, and even then
only if B::Deparse can reconstruct your code. This functionality uses either Storable
or Data::Dumper behind the scenes, depending on which is available (Storable is
preferred).
undirected_copy
undirected_copy_graph
my $c = $g->undirected_copy_graph;
Create an undirected shallow copy (vertices and edges) of the directed graph so that
for any directed edge (u, v) there is an undirected edge (u, v).
undirected_copy_clear_cache
@path = $g->undirected_copy_clear_cache;
See "Clearing cached results".
directed_copy
directed_copy_graph
my $c = $g->directed_copy_graph;
Create a directed shallow copy (vertices and edges) of the undirected graph so that
for any undirected edge (u, v) there are two directed edges (u, v) and (v, u).
transpose
transpose_graph
my $t = $g->transpose_graph;
Create a directed shallow transposed copy (vertices and edges) of the directed graph
so that for any directed edge (u, v) there is a directed edge (v, u).
You can also transpose a single edge with
transpose_edge
$g->transpose_edge($u, $v)
complete_graph
complete
my $c = $g->complete_graph;
Create a complete graph that has the same vertices as the original graph. A complete
graph has an edge between every pair of vertices.
complement_graph
complement
my $c = $g->complement_graph;
Create a complement graph that has the same vertices as the original graph. A
complement graph has an edge (u,v) if and only if the original graph does not have
edge (u,v).
See also "random_graph" for a random constructor.
Basics
add_vertex
$g->add_vertex($v)
Add the vertex to the graph. Returns the graph.
By default idempotent, but a graph can be created countvertexed.
A vertex is also known as a node.
Adding "undef" as vertex is not allowed.
Note that unless you have isolated vertices (or countvertexed vertices), you do not
need to explicitly use "add_vertex" since "add_edge" will implicitly add its vertices.
add_edge
$g->add_edge($u, $v)
Add the edge to the graph. Implicitly first adds the vertices if the graph does not
have them. Returns the graph.
By default idempotent, but a graph can be created countedged.
An edge is also known as an arc.
has_vertex
$g->has_vertex($v)
Return true if the vertex exists in the graph, false otherwise.
has_edge
$g->has_edge($u, $v)
Return true if the edge exists in the graph, false otherwise.
delete_vertex
$g->delete_vertex($v)
Delete the vertex from the graph. Returns the graph, even if the vertex did not exist
in the graph.
If the graph has been created multivertexed or countvertexed and a vertex has been
added multiple times, the vertex will require at least an equal number of deletions to
become completely deleted.
delete_vertices
$g->delete_vertices($v1, $v2, ...)
Delete the vertices from the graph. Returns the graph.
If the graph has been created multivertexed or countvertexed and a vertex has been
added multiple times, the vertex will require at least an equal number of deletions to
become completely deleteted.
delete_edge
$g->delete_edge($u, $v)
Delete the edge from the graph. Returns the graph, even if the edge did not exist in
the graph.
If the graph has been created multivertexed or countedged and an edge has been added
multiple times, the edge will require at least an equal number of deletions to become
completely deleted.
delete_edges
$g->delete_edges($u1, $v1, $u2, $v2, ...)
Delete the edges from the graph. Returns the graph.
If the graph has been created multivertexed or countedged and an edge has been added
multiple times, the edge will require at least an equal number of deletions to become
completely deleted.
Displaying
Graphs have stringification overload, so you can do things like
print "The graph is $g\n"
One-way (directed, unidirected) edges are shown as '-', two-way (undirected, bidirected)
edges are shown as '='. If you want to, you can call the stringification via the method
stringify
Comparing
Testing for equality can be done either by the overloaded "eq" operator
$g eq "a-b,a-c,d"
or by the method
eq
$g->eq("a-b,a-c,d")
The equality testing compares the stringified forms, and therefore it assumes total
equality, not isomorphism: all the vertices must be named the same, and they must have
identical edges between them.
For unequality there are correspondingly the overloaded "ne" operator and the method
ne
$g->ne("a-b,a-c,d")
See also "Isomorphism".
Paths and Cycles
Paths and cycles are simple extensions of edges: paths are edges starting from where the
previous edge ended, and cycles are paths returning back to the start vertex of the first
edge.
add_path
$g->add_path($a, $b, $c, ..., $x, $y, $z)
Add the edges $a-$b, $b-$c, ..., $x-$y, $y-$z to the graph. Returns the graph.
has_path
$g->has_path($a, $b, $c, ..., $x, $y, $z)
Return true if the graph has all the edges $a-$b, $b-$c, ..., $x-$y, $y-$z, false
otherwise.
delete_path
$g->delete_path($a, $b, $c, ..., $x, $y, $z)
Delete all the edges edges $a-$b, $b-$c, ..., $x-$y, $y-$z (regardless of whether they
exist or not). Returns the graph.
add_cycle
$g->add_cycle($a, $b, $c, ..., $x, $y, $z)
Add the edges $a-$b, $b-$c, ..., $x-$y, $y-$z, and $z-$a to the graph. Returns the
graph.
has_cycle
$g->has_cycle($a, $b, $c, ..., $x, $y, $z)
Return true if the graph has all the edges $a-$b, $b-$c, ..., $x-$y, $y-$z, and $z-$a,
false otherwise.
NOTE: This does not detect cycles, see "has_a_cycle" and "find_a_cycle".
delete_cycle
$g->delete_cycle($a, $b, $c, ..., $x, $y, $z)
Delete all the edges edges $a-$b, $b-$c, ..., $x-$y, $y-$z, and $z-$a (regardless of
whether they exist or not). Returns the graph.
has_a_cycle
$g->has_a_cycle
Returns true if the graph has a cycle, false if not.
find_a_cycle
$g->find_a_cycle
Returns a cycle if the graph has one (as a list of vertices), an empty list if no
cycle can be found.
Note that this just returns the vertices of a cycle: not any particular cycle, just
the first one it finds. A repeated call might find the same cycle, or it might find a
different one, and you cannot call this repeatedly to find all the cycles.
Graph Types
is_simple_graph
$g->is_simple_graph
Return true if the graph has no multiedges, false otherwise.
is_pseudo_graph
$g->is_pseudo_graph
Return true if the graph has any multiedges or any self-loops, false otherwise.
is_multi_graph
$g->is_multi_graph
Return true if the graph has any multiedges but no self-loops, false otherwise.
is_directed_acyclic_graph
is_dag
$g->is_directed_acyclic_graph
$g->is_dag
Return true if the graph is directed and acyclic, false otherwise.
is_cyclic
$g->is_cyclic
Return true if the graph is cyclic (contains at least one cycle). (This is identical
to "has_a_cycle".)
To find at least that one cycle, see "find_a_cycle".
is_acyclic
Return true if the graph is acyclic (does not contain any cycles).
To find a cycle, use "find_a_cycle".
Transitivity
is_transitive
$g->is_transitive
Return true if the graph is transitive, false otherwise.
TransitiveClosure_Floyd_Warshall
transitive_closure
$tcg = $g->TransitiveClosure_Floyd_Warshall
Return the transitive closure graph of the graph.
You can query the reachability from $u to $v with
is_reachable
$tcg->is_reachable($u, $v)
See Graph::TransitiveClosure for more information about creating and querying transitive
closures.
With
transitive_closure_matrix
$tcm = $g->transitive_closure_matrix;
you can (create if not existing and) query the transitive closure matrix that underlies
the transitive closure graph. See Graph::TransitiveClosure::Matrix for more information.
Mutators
add_vertices
$g->add_vertices('d', 'e', 'f')
Add zero or more vertices to the graph. Returns the graph.
add_edges
$g->add_edges(['d', 'e'], ['f', 'g'])
$g->add_edges(qw(d e f g));
Add zero or more edges to the graph. The edges are specified as a list of array
references, or as a list of vertices where the even (0th, 2nd, 4th, ...) items are
start vertices and the odd (1st, 3rd, 5th, ...) are the corresponding end vertices.
Returns the graph.
Accessors
is_directed
directed
$g->is_directed()
$g->directed()
Return true if the graph is directed, false otherwise.
is_undirected
undirected
$g->is_undirected()
$g->undirected()
Return true if the graph is undirected, false otherwise.
is_refvertexed
is_refvertexed_stringified
refvertexed
refvertexed_stringified
Return true if the graph can handle references (including Perl objects) as vertices.
vertices
my $V = $g->vertices
my @V = $g->vertices
In scalar context, return the number of vertices in the graph. In list context,
return the vertices, in no particular order.
has_vertices
$g->has_vertices()
Return true if the graph has any vertices, false otherwise.
edges
my $E = $g->edges
my @E = $g->edges
In scalar context, return the number of edges in the graph. In list context, return
the edges, in no particular order. The edges are returned as anonymous arrays listing
the vertices.
has_edges
$g->has_edges()
Return true if the graph has any edges, false otherwise.
is_connected
$g->is_connected
For an undirected graph, return true is the graph is connected, false otherwise.
Being connected means that from every vertex it is possible to reach every other
vertex.
If the graph has been created with a true "unionfind" parameter, the time complexity
is (essentially) O(V), otherwise O(V log V).
See also "connected_components", "connected_component_by_index",
"connected_component_by_vertex", and "same_connected_components", and
"biconnectivity".
For directed graphs, see "is_strongly_connected" and "is_weakly_connected".
connected_components
@cc = $g->connected_components()
For an undirected graph, returns the vertices of the connected components of the graph
as a list of anonymous arrays. The ordering of the anonymous arrays or the ordering
of the vertices inside the anonymous arrays (the components) is undefined.
For directed graphs, see "strongly_connected_components" and
"weakly_connected_components".
connected_component_by_vertex
$i = $g->connected_component_by_vertex($v)
For an undirected graph, return an index identifying the connected component the
vertex belongs to, the indexing starting from zero.
For the inverse, see "connected_component_by_index".
If the graph has been created with a true "unionfind" parameter, the time complexity
is (essentially) O(1), otherwise O(V log V).
See also "biconnectivity".
For directed graphs, see "strongly_connected_component_by_vertex" and
"weakly_connected_component_by_vertex".
connected_component_by_index
@v = $g->connected_component_by_index($i)
For an undirected graph, return the vertices of the ith connected component, the
indexing starting from zero. The order of vertices is undefined, while the order of
the connected components is same as from connected_components().
For the inverse, see "connected_component_by_vertex".
For directed graphs, see "strongly_connected_component_by_index" and
"weakly_connected_component_by_index".
same_connected_components
$g->same_connected_components($u, $v, ...)
For an undirected graph, return true if the vertices are in the same connected
component.
If the graph has been created with a true "unionfind" parameter, the time complexity
is (essentially) O(1), otherwise O(V log V).
For directed graphs, see "same_strongly_connected_components" and
"same_weakly_connected_components".
connected_graph
$cg = $g->connected_graph
For an undirected graph, return its connected graph.
connectivity_clear_cache
$g->connectivity_clear_cache
See "Clearing cached results".
See "Connected Graphs and Their Components" for further discussion.
biconnectivity
my ($ap, $bc, $br) = $g->biconnectivity
For an undirected graph, return the various biconnectivity components of the graph:
the articulation points (cut vertices), biconnected components, and bridges.
Note: currently only handles connected graphs.
is_biconnected
$g->is_biconnected
For an undirected graph, return true if the graph is biconnected (if it has no
articulation points, also known as cut vertices).
is_edge_connected
$g->is_edge_connected
For an undirected graph, return true if the graph is edge-connected (if it has no
bridges).
Note: more precisely, this would be called is_edge_biconnected, since there is a more
general concept of being k-connected.
is_edge_separable
$g->is_edge_separable
For an undirected graph, return true if the graph is edge-separable (if it has
bridges).
Note: more precisely, this would be called is_edge_biseparable, since there is a more
general concept of being k-connected.
articulation_points
cut_vertices
$g->articulation_points
For an undirected graph, return the articulation points (cut vertices) of the graph as
a list of vertices. The order is undefined.
biconnected_components
$g->biconnected_components
For an undirected graph, return the biconnected components of the graph as a list of
anonymous arrays of vertices in the components. The ordering of the anonymous arrays
or the ordering of the vertices inside the anonymous arrays (the components) is
undefined. Also note that one vertex can belong to more than one biconnected
component.
biconnected_component_by_vertex
$i = $g->biconnected_component_by_index($v)
For an undirected graph, return the indices identifying the biconnected components the
vertex belongs to, the indexing starting from zero. The order of of the components is
undefined.
For the inverse, see "connected_component_by_index".
For directed graphs, see "strongly_connected_component_by_index" and
"weakly_connected_component_by_index".
biconnected_component_by_index
@v = $g->biconnected_component_by_index($i)
For an undirected graph, return the vertices in the ith biconnected component of the
graph as an anonymous arrays of vertices in the component. The ordering of the
vertices within a component is undefined. Also note that one vertex can belong to
more than one biconnected component.
same_biconnected_components
$g->same_biconnected_components($u, $v, ...)
For an undirected graph, return true if the vertices are in the same biconnected
component.
biconnected_graph
$bcg = $g->biconnected_graph
For an undirected graph, return its biconnected graph.
See "Connected Graphs and Their Components" for further discussion.
bridges
$g->bridges
For an undirected graph, return the bridges of the graph as a list of anonymous arrays
of vertices in the bridges. The order of bridges and the order of vertices in them is
undefined.
biconnectivity_clear_cache
$g->biconnectivity_clear_cache
See "Clearing cached results".
strongly_connected
is_strongly_connected
$g->is_strongly_connected
For a directed graph, return true is the directed graph is strongly connected, false
if not.
See also "is_weakly_connected".
For undirected graphs, see "is_connected", or "is_biconnected".
strongly_connected_component_by_vertex
$i = $g->strongly_connected_component_by_vertex($v)
For a directed graph, return an index identifying the strongly connected component the
vertex belongs to, the indexing starting from zero.
For the inverse, see "strongly_connected_component_by_index".
See also "weakly_connected_component_by_vertex".
For undirected graphs, see "connected_components" or "biconnected_components".
strongly_connected_component_by_index
@v = $g->strongly_connected_component_by_index($i)
For a directed graph, return the vertices of the ith connected component, the indexing
starting from zero. The order of vertices within a component is undefined, while the
order of the connected components is the as from strongly_connected_components().
For the inverse, see "strongly_connected_component_by_vertex".
For undirected graphs, see "weakly_connected_component_by_index".
same_strongly_connected_components
$g->same_strongly_connected_components($u, $v, ...)
For a directed graph, return true if the vertices are in the same strongly connected
component.
See also "same_weakly_connected_components".
For undirected graphs, see "same_connected_components" or
"same_biconnected_components".
strong_connectivity_clear_cache
$g->strong_connectivity_clear_cache
See "Clearing cached results".
weakly_connected
is_weakly_connected
$g->is_weakly_connected
For a directed graph, return true is the directed graph is weakly connected, false if
not.
Weakly connected graph is also known as semiconnected graph.
See also "is_strongly_connected".
For undirected graphs, see "is_connected" or "is_biconnected".
weakly_connected_components
@wcc = $g->weakly_connected_components()
For a directed graph, returns the vertices of the weakly connected components of the
graph as a list of anonymous arrays. The ordering of the anonymous arrays or the
ordering of the vertices inside the anonymous arrays (the components) is undefined.
See also "strongly_connected_components".
For undirected graphs, see "connected_components" or "biconnected_components".
weakly_connected_component_by_vertex
$i = $g->weakly_connected_component_by_vertex($v)
For a directed graph, return an index identifying the weakly connected component the
vertex belongs to, the indexing starting from zero.
For the inverse, see "weakly_connected_component_by_index".
For undirected graphs, see "connected_component_by_vertex" and
"biconnected_component_by_vertex".
weakly_connected_component_by_index
@v = $g->weakly_connected_component_by_index($i)
For a directed graph, return the vertices of the ith weakly connected component, the
indexing starting zero. The order of vertices within a component is undefined, while
the order of the weakly connected components is same as from
weakly_connected_components().
For the inverse, see "weakly_connected_component_by_vertex".
For undirected graphs, see connected_component_by_index and
biconnected_component_by_index.
same_weakly_connected_components
$g->same_weakly_connected_components($u, $v, ...)
Return true if the vertices are in the same weakly connected component.
weakly_connected_graph
$wcg = $g->weakly_connected_graph
For a directed graph, return its weakly connected graph.
For undirected graphs, see "connected_graph" and "biconnected_graph".
strongly_connected_components
my @scc = $g->strongly_connected_components;
For a directed graph, return the strongly connected components as a list of anonymous
arrays. The elements in the anonymous arrays are the vertices belonging to the
strongly connected component; both the elements and the components are in no
particular order.
Note that strongly connected components can have single-element components even
without self-loops: if a vertex is any of isolated, sink, or a source, the vertex is
alone in its own strong component.
See also "weakly_connected_components".
For undirected graphs, see "connected_components", or see "biconnected_components".
strongly_connected_graph
my $scg = $g->strongly_connected_graph;
See "Connected Graphs and Their Components" for further discussion.
Strongly connected graphs are also known as kernel graphs.
See also "weakly_connected_graph".
For undirected graphs, see "connected_graph", or "biconnected_graph".
is_sink_vertex
$g->is_sink_vertex($v)
Return true if the vertex $v is a sink vertex, false if not. A sink vertex is defined
as a vertex with predecessors but no successors: this definition means that isolated
vertices are not sink vertices. If you want also isolated vertices, use
is_successorless_vertex().
is_source_vertex
$g->is_source_vertex($v)
Return true if the vertex $v is a source vertex, false if not. A source vertex is
defined as a vertex with successors but no predecessors: the definition means that
isolated vertices are not source vertices. If you want also isolated vertices, use
is_predecessorless_vertex().
is_successorless_vertex
$g->is_successorless_vertex($v)
Return true if the vertex $v has no succcessors (no edges leaving the vertex), false
if it has.
Isolated vertices will return true: if you do not want this, use is_sink_vertex().
is_successorful_vertex
$g->is_successorful_vertex($v)
Return true if the vertex $v has successors, false if not.
is_predecessorless_vertex
$g->is_predecessorless_vertex($v)
Return true if the vertex $v has no predecessors (no edges entering the vertex), false
if it has.
Isolated vertices will return true: if you do not want this, use is_source_vertex().
is_predecessorful_vertex
$g->is_predecessorful_vertex($v)
Return true if the vertex $v has predecessors, false if not.
is_isolated_vertex
$g->is_isolated_vertex($v)
Return true if the vertex $v is an isolated vertex: no successors and no predecessors.
is_interior_vertex
$g->is_interior_vertex($v)
Return true if the vertex $v is an interior vertex: both successors and predecessors.
is_exterior_vertex
$g->is_exterior_vertex($v)
Return true if the vertex $v is an exterior vertex: has either no successors or no
predecessors, or neither.
is_self_loop_vertex
$g->is_self_loop_vertex($v)
Return true if the vertex $v is a self loop vertex: has an edge from itself to itself.
sink_vertices
@v = $g->sink_vertices()
Return the sink vertices of the graph. In scalar context return the number of sink
vertices. See "is_sink_vertex" for the definition of a sink vertex.
source_vertices
@v = $g->source_vertices()
Return the source vertices of the graph. In scalar context return the number of
source vertices. See "is_source_vertex" for the definition of a source vertex.
successorful_vertices
@v = $g->successorful_vertices()
Return the successorful vertices of the graph. In scalar context return the number of
successorful vertices.
successorless_vertices
@v = $g->successorless_vertices()
Return the successorless vertices of the graph. In scalar context return the number
of successorless vertices.
successors
@s = $g->successors($v)
Return the immediate successor vertices of the vertex.
See also "all_successors", "all_neighbours", and "all_reachable".
all_successors
@s = $g->all_successors(@v)
For a directed graph, returns all successor vertices of the argument vertices,
recursively.
For undirected graphs, see "all_neighbours" and "all_reachable".
See also "successors".
neighbors
neighbours
@n = $g->neighbours($v)
Return the neighboring/neighbouring vertices. Also known as the adjacent vertices.
See also "all_neighbours" and "all_reachable".
all_neighbors
all_neighbours
@n = $g->all_neighbours(@v)
Return the neighboring/neighbouring vertices of the argument vertices, recursively.
For a directed graph, recurses up predecessors and down successors. For an undirected
graph, returns all the vertices reachable from the argument vertices: equivalent to
"all_reachable".
See also "neighbours" and "all_reachable".
all_reachable
@r = $g->all_reachable(@v)
Return all the vertices reachable from of the argument vertices, recursively. For a
directed graph, equivalent to "all_successors". For an undirected graph, equivalent
to "all_neighbours". The argument vertices are not included in the results unless
there are explicit self-loops.
See also "neighbours", "all_neighbours", and "all_successors".
predecessorful_vertices
@v = $g->predecessorful_vertices()
Return the predecessorful vertices of the graph. In scalar context return the number
of predecessorful vertices.
predecessorless_vertices
@v = $g->predecessorless_vertices()
Return the predecessorless vertices of the graph. In scalar context return the number
of predecessorless vertices.
predecessors
@p = $g->predecessors($v)
Return the immediate predecessor vertices of the vertex.
See also "all_predecessors", "all_neighbours", and "all_reachable".
all_predecessors
@p = $g->all_predecessors(@v)
For a directed graph, returns all predecessor vertices of the argument vertices,
recursively.
For undirected graphs, see "all_neighbours" and "all_reachable".
See also "predecessors".
isolated_vertices
@v = $g->isolated_vertices()
Return the isolated vertices of the graph. In scalar context return the number of
isolated vertices. See "is_isolated_vertex" for the definition of an isolated vertex.
interior_vertices
@v = $g->interior_vertices()
Return the interior vertices of the graph. In scalar context return the number of
interior vertices. See "is_interior_vertex" for the definition of an interior vertex.
exterior_vertices
@v = $g->exterior_vertices()
Return the exterior vertices of the graph. In scalar context return the number of
exterior vertices. See "is_exterior_vertex" for the definition of an exterior vertex.
self_loop_vertices
@v = $g->self_loop_vertices()
Return the self-loop vertices of the graph. In scalar context return the number of
self-loop vertices. See "is_self_loop_vertex" for the definition of a self-loop
vertex.
Connected Graphs and Their Components
In this discussion connected graph refers to any of connected graphs, biconnected graphs,
and strongly connected graphs.
NOTE: if the vertices of the original graph are Perl objects, (in other words, references,
so you must be using "refvertexed") the vertices of the connected graph are NOT by default
usable as Perl objects because they are blessed into a package with a rather unusable
name.
By default, the vertex names of the connected graph are formed from the names of the
vertices of the original graph by (alphabetically sorting them and) concatenating their
names with "+". The vertex attribute "subvertices" is also used to store the list (as an
array reference) of the original vertices. To change the 'supercomponent' vertex names
and the whole logic of forming these supercomponents use the "super_component") option to
the method calls:
$g->connected_graph(super_component => sub { ... })
$g->biconnected_graph(super_component => sub { ... })
$g->strongly_connected_graph(super_component => sub { ... })
The subroutine reference gets the 'subcomponents' (the vertices of the original graph) as
arguments, and it is supposed to return the new supercomponent vertex, the "stringified"
form of which is used as the vertex name.
Degree
A vertex has a degree based on the number of incoming and outgoing edges. This really
makes sense only for directed graphs.
degree
vertex_degree
$d = $g->degree($v)
$d = $g->vertex_degree($v)
For directed graphs: the in-degree minus the out-degree at the vertex.
For undirected graphs: the number of edges at the vertex (identical to "in_degree()",
"out_degree()").
in_degree
$d = $g->in_degree($v)
For directed graphs: the number of incoming edges at the vertex.
For undirected graphs: the number of edges at the vertex (identical to "out_degree()",
"degree()", "vertex_degree()").
out_degree
$o = $g->out_degree($v)
For directed graphs: The number of outgoing edges at the vertex.
For undirected graphs: the number of edges at the vertex (identical to "in_degree()",
"degree()", "vertex_degree()").
average_degree
my $ad = $g->average_degree;
Return the average degree (as in "degree()" or "vertex_degree()") taken over all
vertices.
Related methods are
edges_at
@e = $g->edges_at($v)
The union of edges from and edges to at the vertex.
edges_from
@e = $g->edges_from($v)
The edges leaving the vertex.
edges_to
@e = $g->edges_to($v)
The edges entering the vertex.
See also "average_degree".
Counted Vertices
Counted vertices are vertices with more than one instance, normally adding vertices is
idempotent. To enable counted vertices on a graph, give the "countvertexed" parameter a
true value
use Graph;
my $g = Graph->new(countvertexed => 1);
To find out how many times the vertex has been added:
get_vertex_count
my $c = $g->get_vertex_count($v);
Return the count of the vertex, or undef if the vertex does not exist.
Multiedges, Multivertices, Multigraphs
Multiedges are edges with more than one "life", meaning that one has to delete them as
many times as they have been added. Normally adding edges is idempotent (in other words,
adding edges more than once makes no difference).
There are two kinds or degrees of creating multiedges and multivertices. The two kinds
are mutually exclusive.
The weaker kind is called counted, in which the edge or vertex has a count on it: add
operations increase the count, and delete operations decrease the count, and once the
count goes to zero, the edge or vertex is deleted. If there are attributes, they all are
attached to the same vertex. You can think of this as the graph elements being
refcounted, or reference counted, if that sounds more familiar.
The stronger kind is called (true) multi, in which the edge or vertex really has multiple
separate identities, so that you can for example attach different attributes to different
instances.
To enable multiedges on a graph:
use Graph;
my $g0 = Graph->new(countedged => 1);
my $g0 = Graph->new(multiedged => 1);
Similarly for vertices
use Graph;
my $g1 = Graph->new(countvertexed => 1);
my $g1 = Graph->new(multivertexed => 1);
You can test for these by
is_countedged
countedged
$g->is_countedged
$g->countedged
Return true if the graph is countedged.
is_countvertexed
countvertexed
$g->is_countvertexed
$g->countvertexed
Return true if the graph is countvertexed.
is_multiedged
multiedged
$g->is_multiedged
$g->multiedged
Return true if the graph is multiedged.
is_multivertexed
multivertexed
$g->is_multivertexed
$g->multivertexed
Return true if the graph is multivertexed.
A multiedged (either the weak kind or the strong kind) graph is a multigraph, for which
you can test with "is_multi_graph()".
NOTE: The various graph algorithms do not in general work well with multigraphs (they
often assume simple graphs, that is, no multiedges or loops), and no effort has been made
to test the algorithms with multigraphs.
vertices() and edges() will return the multiple elements: if you want just the unique
elements, use
unique_vertices
unique_edges
@uv = $g->unique_vertices; # unique
@mv = $g->vertices; # possible multiples
@ue = $g->unique_edges;
@me = $g->edges;
If you are using (the stronger kind of) multielements, you should use the by_id variants:
add_vertex_by_id
has_vertex_by_id
delete_vertex_by_id
add_edge_by_id
has_edge_by_id
delete_edge_by_id
$g->add_vertex_by_id($v, $id)
$g->has_vertex_by_id($v, $id)
$g->delete_vertex_by_id($v, $id)
$g->add_edge_by_id($u, $v, $id)
$g->has_edge_by_id($u, $v, $id)
$g->delete_edge_by_id($u, $v, $id)
These interfaces only apply to multivertices and multiedges. When you delete the last
vertex/edge in a multivertex/edge, the whole vertex/edge is deleted. You can use
add_vertex()/add_edge() on a multivertex/multiedge graph, in which case an id is generated
automatically. To find out which the generated id was, you need to use
add_vertex_get_id
add_edge_get_id
$idv = $g->add_vertex_get_id($v)
$ide = $g->add_edge_get_id($u, $v)
To return all the ids of vertices/edges in a multivertex/multiedge, use
get_multivertex_ids
get_multiedge_ids
$g->get_multivertex_ids($v)
$g->get_multiedge_ids($u, $v)
The ids are returned in random order.
To find out how many times the edge has been added (this works for either kind of
multiedges):
get_edge_count
my $c = $g->get_edge_count($u, $v);
Return the count (the "countedness") of the edge, or undef if the edge does not exist.
The following multi-entity utility functions exist, mirroring the non-multi vertices and
edges:
add_weighted_edge_by_id
add_weighted_edges_by_id
add_weighted_path_by_id
add_weighted_vertex_by_id
add_weighted_vertices_by_id
delete_edge_weight_by_id
delete_vertex_weight_by_id
get_edge_weight_by_id
get_vertex_weight_by_id
has_edge_weight_by_id
has_vertex_weight_by_id
set_edge_weight_by_id
set_vertex_weight_by_id
Topological Sort
topological_sort
toposort
my @ts = $g->topological_sort;
Return the vertices of the graph sorted topologically. Note that there may be several
possible topological orderings; one of them is returned.
If the graph contains a cycle, a fatal error is thrown, you can either use "eval" to
trap that, or supply the "empty_if_cyclic" argument with a true value
my @ts = $g->topological_sort(empty_if_cyclic => 1);
in which case an empty array is returned if the graph is cyclic.
Minimum Spanning Trees (MST)
Minimum Spanning Trees or MSTs are tree subgraphs derived from an undirected graph. MSTs
"span the graph" (covering all the vertices) using as lightly weighted (hence the
"minimum") edges as possible.
MST_Kruskal
$mstg = $g->MST_Kruskal;
Returns the Kruskal MST of the graph.
MST_Prim
$mstg = $g->MST_Prim(%opt);
Returns the Prim MST of the graph.
You can choose the first vertex with $opt{ first_root }.
MST_Dijkstra
minimum_spanning_tree
$mstg = $g->MST_Dijkstra;
$mstg = $g->minimum_spanning_tree;
Aliases for MST_Prim.
Single-Source Shortest Paths (SSSP)
Single-source shortest paths, also known as Shortest Path Trees (SPTs). For either a
directed or an undirected graph, return a (tree) subgraph that from a single start vertex
(the "single source") travels the shortest possible paths (the paths with the lightest
weights) to all the other vertices. Note that the SSSP is neither reflexive (the shortest
paths do not include the zero-length path from the source vertex to the source vertex) nor
transitive (the shortest paths do not include transitive closure paths). If no weight is
defined for an edge, 1 (one) is assumed.
SPT_Dijkstra
$sptg = $g->SPT_Dijkstra($root)
$sptg = $g->SPT_Dijkstra(%opt)
Return as a graph the the single-source shortest paths of the graph using Dijkstra's
algorithm. The graph cannot contain negative edges (negative edges cause the
algorithm to abort with an error message "Graph::SPT_Dijkstra: edge ... is negative").
You can choose the first vertex of the result with either a single vertex argument or
with $opt{ first_root }, otherwise a random vertex is chosen.
NOTE: note that all the vertices might not be reachable from the selected (explicit or
random) start vertex.
The start vertex is be available as the graph attribute "SPT_Dijkstra_root").
The result weights of vertices can be retrieved from the result graph by
my $w = $sptg->get_vertex_attribute($v, 'weight');
The predecessor vertex of a vertex in the result graph can be retrieved by
my $u = $sptg->get_vertex_attribute($v, 'p');
("A successor vertex" cannot be retrieved as simply because a single vertex can have
several successors. You can first find the "neighbors()" vertices and then remove the
predecessor vertex.)
If you want to find the shortest path between two vertices, see "SP_Dijkstra".
SSSP_Dijkstra
single_source_shortest_paths
Aliases for SPT_Dijkstra.
SP_Dijkstra
@path = $g->SP_Dijkstra($u, $v)
Return the vertices in the shortest path in the graph $g between the two vertices $u,
$v. If no path can be found, an empty list is returned.
Uses SPT_Dijkstra().
SPT_Dijkstra_clear_cache
$g->SPT_Dijkstra_clear_cache
See "Clearing cached results".
SPT_Bellman_Ford
$sptg = $g->SPT_Bellman_Ford(%opt)
Return as a graph the single-source shortest paths of the graph using Bellman-Ford's
algorithm. The graph can contain negative edges but not negative cycles (negative
cycles cause the algorithm to abort with an error message "Graph::SPT_Bellman_Ford:
negative cycle exists/").
You can choose the start vertex of the result with either a single vertex argument or
with $opt{ first_root }, otherwise a random vertex is chosen.
NOTE: note that all the vertices might not be reachable from the selected (explicit or
random) start vertex.
The start vertex is be available as the graph attribute "SPT_Bellman_Ford_root").
The result weights of vertices can be retrieved from the result graph by
my $w = $sptg->get_vertex_attribute($v, 'weight');
The predecessor vertex of a vertex in the result graph can be retrieved by
my $u = $sptg->get_vertex_attribute($v, 'p');
("A successor vertex" cannot be retrieved as simply because a single vertex can have
several successors. You can first find the "neighbors()" vertices and then remove the
predecessor vertex.)
If you want to find the shortes path between two vertices, see "SP_Bellman_Ford".
SSSP_Bellman_Ford
Alias for SPT_Bellman_Ford.
SP_Bellman_Ford
@path = $g->SP_Bellman_Ford($u, $v)
Return the vertices in the shortest path in the graph $g between the two vertices $u,
$v. If no path can be found, an empty list is returned.
Uses SPT_Bellman_Ford().
SPT_Bellman_Ford_clear_cache
$g->SPT_Bellman_Ford_clear_cache
See "Clearing cached results".
All-Pairs Shortest Paths (APSP)
For either a directed or an undirected graph, return the APSP object describing all the
possible paths between any two vertices of the graph. If no weight is defined for an
edge, 1 (one) is assumed.
APSP_Floyd_Warshall
all_pairs_shortest_paths
my $apsp = $g->APSP_Floyd_Warshall(...);
Return the all-pairs shortest path object computed from the graph using Floyd-
Warshall's algorithm. The length of a path between two vertices is the sum of weight
attribute of the edges along the shortest path between the two vertices. If no weight
attribute name is specified explicitly
$g->APSP_Floyd_Warshall(attribute_name => 'height');
the attribute "weight" is assumed.
If an edge has no defined weight attribute, the value of one is assumed when getting
the attribute.
Once computed, you can query the APSP object with
path_length
my $l = $apsp->path_length($u, $v);
Return the length of the shortest path between the two vertices.
path_vertices
my @v = $apsp->path_vertices($u, $v);
Return the list of vertices along the shortest path.
path_predecessor
my $u = $apsp->path_predecessor($v);
Returns the predecessor of vertex $v in the all-pairs shortest paths.
average_path_length
my $apl = $g->average_path_length; # All vertex pairs.
my $apl = $g->average_path_length($u); # From $u.
my $apl = $g->average_path_length($u, undef); # From $u.
my $apl = $g->average_path_length($u, $v); # From $u to $v.
my $apl = $g->average_path_length(undef, $v); # To $v.
Return the average (shortest) path length over all the vertex pairs of the
graph, from a vertex, between two vertices, and to a vertex.
longest_path
my @lp = $g->longest_path;
my $lp = $g->longest_path;
In scalar context return the longest shortest path length over all the vertex
pairs of the graph. In list context return the vertices along a longest
shortest path. Note that there might be more than one such path; this
interfaces return a random one of them.
diameter
graph_diameter
my $gd = $g->diameter;
The longest path over all the vertex pairs is known as the graph diameter.
shortest_path
my @sp = $g->shortest_path;
my $sp = $g->shortest_path;
In scalar context return the shortest length over all the vertex pairs of the
graph. In list context return the vertices along a shortest path. Note that
there might be more than one such path; this interface returns a random one of
them.
radius
my $gr = $g->radius;
The shortest longest path over all the vertex pairs is known as the graph
radius. See also "diameter".
center_vertices
centre_vertices
my @c = $g->center_vertices;
my @c = $g->center_vertices($delta);
The graph center is the set of vertices for which the vertex eccentricity is
equal to the graph radius. The vertices are returned in random order. By
specifying a delta value you can widen the criterion from strict equality
(handy for non-integer edge weights).
vertex_eccentricity
my $ve = $g->vertex_eccentricity($v);
The longest path to a vertex is known as the vertex eccentricity. If the
graph is unconnected, returns Inf.
You can walk through the matrix of the shortest paths by using
for_shortest_paths
$n = $g->for_shortest_paths($callback)
The number of shortest paths is returned (this should be equal to V*V). The
$callback is a sub reference that receives four arguments: the transitive closure
object from Graph::TransitiveClosure, the two vertices, and the index to the
current shortest paths (0..V*V-1).
Clearing cached results
For many graph algorithms there are several different but equally valid results.
(Pseudo)Randomness is used internally by the Graph module to for example pick a random
starting vertex, and to select random edges from a vertex.
For efficiency the computed result is often cached to avoid recomputing the potentially
expensive operation, and this also gives additional determinism (once a correct result has
been computed, the same result will always be given).
However, sometimes the exact opposite is desireable, and the possible alternative results
are wanted (within the limits of the pseudorandomness: not all the possible solutions are
guaranteed to be returned, usually only a subset is retuned). To undo the caching, the
following methods are available:
• connectivity_clear_cache
Affects "connected_components", "connected_component_by_vertex",
"connected_component_by_index", "same_connected_components", "connected_graph",
"is_connected", "is_weakly_connected", "weakly_connected_components",
"weakly_connected_component_by_vertex", "weakly_connected_component_by_index",
"same_weakly_connected_components", "weakly_connected_graph".
• biconnectivity_clear_cache
Affects "biconnected_components", "biconnected_component_by_vertex",
"biconnected_component_by_index", "is_edge_connected", "is_edge_separable",
"articulation_points", "cut_vertices", "is_biconnected", "biconnected_graph",
"same_biconnected_components", "bridges".
• strong_connectivity_clear_cache
Affects "strongly_connected_components", "strongly_connected_component_by_vertex",
"strongly_connected_component_by_index", "same_strongly_connected_components",
"is_strongly_connected", "strongly_connected", "strongly_connected_graph".
• SPT_Dijkstra_clear_cache
Affects "SPT_Dijkstra", "SSSP_Dijkstra", "single_source_shortest_paths",
"SP_Dijkstra".
• SPT_Bellman_Ford_clear_cache
Affects "SPT_Bellman_Ford", "SSSP_Bellman_Ford", "SP_Bellman_Ford".
Note that any such computed and cached results are of course always automatically
discarded whenever the graph is modified.
Random
You can either ask for random elements of existing graphs or create random graphs.
random_vertex
my $v = $g->random_vertex;
Return a random vertex of the graph, or undef if there are no vertices.
random_edge
my $e = $g->random_edge;
Return a random edge of the graph as an array reference having the vertices as
elements, or undef if there are no edges.
random_successor
my $v = $g->random_successor($v);
Return a random successor of the vertex in the graph, or undef if there are no
successors.
random_predecessor
my $u = $g->random_predecessor($v);
Return a random predecessor of the vertex in the graph, or undef if there are no
predecessors.
random_graph
my $g = Graph->random_graph(%opt);
Construct a random graph. The %opt must contain the "vertices" argument
vertices => vertices_def
where the vertices_def is one of
• an array reference where the elements of the array reference are the vertices
• a number N in which case the vertices will be integers 0..N-1
The %opt may have either of the argument "edges" or the argument "edges_fill". Both are
used to define how many random edges to add to the graph; "edges" is an absolute number,
while "edges_fill" is a relative number (relative to the number of edges in a complete
graph, C). The number of edges can be larger than C, but only if the graph is countedged.
The random edges will not include self-loops. If neither "edges" nor "edges_fill" is
specified, an "edges_fill" of 0.5 is assumed.
If you want repeatable randomness (what is an oxymoron?) you can use the "random_seed"
option:
$g = Graph->random_graph(vertices => 10, random_seed => 1234);
As this uses the standard Perl srand(), the usual caveat applies: use it sparingly, and
consider instead using a single srand() call at the top level of your application.
The default random distribution of edges is flat, that is, any pair of vertices is equally
likely to appear. To define your own distribution, use the "random_edge" option:
$g = Graph->random_graph(vertices => 10, random_edge => \&d);
where "d" is a code reference receiving ($g, $u, $v, $p) as parameters, where the $g is
the random graph, $u and $v are the vertices, and the $p is the probability ([0,1]) for a
flat distribution. It must return a probability ([0,1]) that the vertices $u and $v have
an edge between them. Note that returning one for a particular pair of vertices doesn't
guarantee that the edge will be present in the resulting graph because the required number
of edges might be reached before that particular pair is tested for the possibility of an
edge. Be very careful to adjust also "edges" or "edges_fill" so that there is a
possibility of the filling process terminating.
Attributes
You can attach free-form attributes (key-value pairs, in effect a full Perl hash) to each
vertex, edge, and the graph itself.
Note that attaching attributes does slow down some other operations on the graph by a
factor of three to ten. For example adding edge attributes does slow down anything that
walks through all the edges.
For vertex attributes:
set_vertex_attribute
$g->set_vertex_attribute($v, $name, $value)
Set the named vertex attribute.
If the vertex does not exist, the set_...() will create it, and the other vertex
attribute methods will return false or empty.
NOTE: any attributes beginning with an underscore/underline (_) are reserved for the
internal use of the Graph module.
get_vertex_attribute
$value = $g->get_vertex_attribute($v, $name)
Return the named vertex attribute.
has_vertex_attribute
$g->has_vertex_attribute($v, $name)
Return true if the vertex has an attribute, false if not.
delete_vertex_attribute
$g->delete_vertex_attribute($v, $name)
Delete the named vertex attribute.
set_vertex_attributes
$g->set_vertex_attributes($v, $attr)
Set all the attributes of the vertex from the anonymous hash $attr.
NOTE: any attributes beginning with an underscore ("_") are reserved for the internal
use of the Graph module.
get_vertex_attributes
$attr = $g->get_vertex_attributes($v)
Return all the attributes of the vertex as an anonymous hash.
get_vertex_attribute_names
@name = $g->get_vertex_attribute_names($v)
Return the names of vertex attributes.
get_vertex_attribute_values
@value = $g->get_vertex_attribute_values($v)
Return the values of vertex attributes.
has_vertex_attributes
$g->has_vertex_attributes($v)
Return true if the vertex has any attributes, false if not.
delete_vertex_attributes
$g->delete_vertex_attributes($v)
Delete all the attributes of the named vertex.
If you are using multivertices, use the by_id variants:
set_vertex_attribute_by_id
get_vertex_attribute_by_id
has_vertex_attribute_by_id
delete_vertex_attribute_by_id
set_vertex_attributes_by_id
get_vertex_attributes_by_id
get_vertex_attribute_names_by_id
get_vertex_attribute_values_by_id
has_vertex_attributes_by_id
delete_vertex_attributes_by_id
$g->set_vertex_attribute_by_id($v, $id, $name, $value)
$g->get_vertex_attribute_by_id($v, $id, $name)
$g->has_vertex_attribute_by_id($v, $id, $name)
$g->delete_vertex_attribute_by_id($v, $id, $name)
$g->set_vertex_attributes_by_id($v, $id, $attr)
$g->get_vertex_attributes_by_id($v, $id)
$g->get_vertex_attribute_values_by_id($v, $id)
$g->get_vertex_attribute_names_by_id($v, $id)
$g->has_vertex_attributes_by_id($v, $id)
$g->delete_vertex_attributes_by_id($v, $id)
For edge attributes:
set_edge_attribute
$g->set_edge_attribute($u, $v, $name, $value)
Set the named edge attribute.
If the edge does not exist, the set_...() will create it, and the other edge attribute
methods will return false or empty.
NOTE: any attributes beginning with an underscore ("_") are reserved for the internal
use of the Graph module.
get_edge_attribute
$value = $g->get_edge_attribute($u, $v, $name)
Return the named edge attribute.
has_edge_attribute
$g->has_edge_attribute($u, $v, $name)
Return true if the edge has an attribute, false if not.
delete_edge_attribute
$g->delete_edge_attribute($u, $v, $name)
Delete the named edge attribute.
set_edge_attributes
$g->set_edge_attributes($u, $v, $attr)
Set all the attributes of the edge from the anonymous hash $attr.
NOTE: any attributes beginning with an underscore ("_") are reserved for the internal
use of the Graph module.
get_edge_attributes
$attr = $g->get_edge_attributes($u, $v)
Return all the attributes of the edge as an anonymous hash.
get_edge_attribute_names
@name = $g->get_edge_attribute_names($u, $v)
Return the names of edge attributes.
get_edge_attribute_values
@value = $g->get_edge_attribute_values($u, $v)
Return the values of edge attributes.
has_edge_attributes
$g->has_edge_attributes($u, $v)
Return true if the edge has any attributes, false if not.
delete_edge_attributes
$g->delete_edge_attributes($u, $v)
Delete all the attributes of the named edge.
If you are using multiedges, use the by_id variants:
set_edge_attribute_by_id
get_edge_attribute_by_id
has_edge_attribute_by_id
delete_edge_attribute_by_id
set_edge_attributes_by_id
get_edge_attributes_by_id
get_edge_attribute_names_by_id
get_edge_attribute_values_by_id
has_edge_attributes_by_id
delete_edge_attributes_by_id
$g->set_edge_attribute_by_id($u, $v, $id, $name, $value)
$g->get_edge_attribute_by_id($u, $v, $id, $name)
$g->has_edge_attribute_by_id($u, $v, $id, $name)
$g->delete_edge_attribute_by_id($u, $v, $id, $name)
$g->set_edge_attributes_by_id($u, $v, $id, $attr)
$g->get_edge_attributes_by_id($u, $v, $id)
$g->get_edge_attribute_values_by_id($u, $v, $id)
$g->get_edge_attribute_names_by_id($u, $v, $id)
$g->has_edge_attributes_by_id($u, $v, $id)
$g->delete_edge_attributes_by_id($u, $v, $id)
For graph attributes:
set_graph_attribute
$g->set_graph_attribute($name, $value)
Set the named graph attribute.
NOTE: any attributes beginning with an underscore ("_") are reserved for the internal
use of the Graph module.
get_graph_attribute
$value = $g->get_graph_attribute($name)
Return the named graph attribute.
has_graph_attribute
$g->has_graph_attribute($name)
Return true if the graph has an attribute, false if not.
delete_graph_attribute
$g->delete_graph_attribute($name)
Delete the named graph attribute.
set_graph_attributes
$g->get_graph_attributes($attr)
Set all the attributes of the graph from the anonymous hash $attr.
NOTE: any attributes beginning with an underscore ("_") are reserved for the internal
use of the Graph module.
get_graph_attributes
$attr = $g->get_graph_attributes()
Return all the attributes of the graph as an anonymous hash.
get_graph_attribute_names
@name = $g->get_graph_attribute_names()
Return the names of graph attributes.
get_graph_attribute_values
@value = $g->get_graph_attribute_values()
Return the values of graph attributes.
has_graph_attributes
$g->has_graph_attributes()
Return true if the graph has any attributes, false if not.
delete_graph_attributes
$g->delete_graph_attributes()
Delete all the attributes of the named graph.
Weighted
As convenient shortcuts the following methods add, query, and manipulate the attribute
"weight" with the specified value to the respective Graph elements.
add_weighted_edge
$g->add_weighted_edge($u, $v, $weight)
add_weighted_edges
$g->add_weighted_edges($u1, $v1, $weight1, ...)
add_weighted_path
$g->add_weighted_path($v1, $weight1, $v2, $weight2, $v3, ...)
add_weighted_vertex
$g->add_weighted_vertex($v, $weight)
add_weighted_vertices
$g->add_weighted_vertices($v1, $weight1, $v2, $weight2, ...)
delete_edge_weight
$g->delete_edge_weight($u, $v)
delete_vertex_weight
$g->delete_vertex_weight($v)
get_edge_weight
$g->get_edge_weight($u, $v)
get_vertex_weight
$g->get_vertex_weight($v)
has_edge_weight
$g->has_edge_weight($u, $v)
has_vertex_weight
$g->has_vertex_weight($v)
set_edge_weight
$g->set_edge_weight($u, $v, $weight)
set_vertex_weight
$g->set_vertex_weight($v, $weight)
Isomorphism
Two graphs being isomorphic means that they are structurally the same graph, the
difference being that the vertices might have been renamed or substituted. For example in
the below example $g0 and $g1 are isomorphic: the vertices "b c d" have been renamed as "z
x y".
$g0 = Graph->new;
$g0->add_edges(qw(a b a c c d));
$g1 = Graph->new;
$g1->add_edges(qw(a x x y a z));
In the general case determining isomorphism is NP-hard, in other words, really hard (time-
consuming), no other ways of solving the problem are known than brute force check of of
all the possibilities (with possible optimization tricks, of course, but brute force still
rules at the end of the day).
A very rough guess at whether two graphs could be isomorphic is possible via the method
could_be_isomorphic
$g0->could_be_isomorphic($g1)
If the graphs do not have the same number of vertices and edges, false is returned. If
the distribution of in-degrees and out-degrees at the vertices of the graphs does not
match, false is returned. Otherwise, true is returned.
What is actually returned is the maximum number of possible isomorphic graphs between the
two graphs, after the above sanity checks have been conducted. It is basically the
product of the factorials of the absolute values of in-degrees and out-degree pairs at
each vertex, with the isolated vertices ignored (since they could be reshuffled and
renamed arbitrarily). Note that for large graphs the product of these factorials can
overflow the maximum presentable number (the floating point number) in your computer (in
Perl) and you might get for example Infinity as the result.
Miscellaneous
betweenness
%b = $g->betweenness
Returns a map of vertices to their Freeman's betweennesses:
C_b(v) = \sum_{s \neq v \neq t \in V} \frac{\sigma_{s,t}(v)}{\sigma_{s,t}}
It is described in:
Freeman, A set of measures of centrality based on betweenness, http://arxiv.org/pdf/cond-mat/0309045
and based on the algorithm from:
"A Faster Algorithm for Betweenness Centrality"
clustering_coefficient
$gamma = $g->clustering_coefficient()
($gamma, %clustering) = $g->clustering_coefficient()
Returns the clustering coefficient gamma as described in
Duncan J. Watts and Steven Strogatz, Collective dynamics of 'small-world' networks, http://audiophile.tam.cornell.edu/SS_nature_smallworld.pdf
In scalar context returns just the average gamma, in list context returns the average
gamma and a hash of vertices to clustering coefficients.
subgraph_by_radius
$s = $g->subgraph_by_radius($n, $radius);
Returns a subgraph representing the ball of $radius around node $n (breadth-first
search).
The "expect" methods can be used to test a graph and croak if the graph is not as
expected.
expect_acyclic
expect_dag
expect_directed
expect_multiedged
expect_multivertexed
expect_non_multiedged
expect_non_multivertexed
expect_non_unionfind
expect_undirected
In many algorithms it is useful to have a value representing the infinity. The Graph
provides (and itself uses):
Infinity
(Not exported, use Graph::Infinity explicitly)
Size Requirements
A graph takes up at least 1172 bytes of memory.
A vertex takes up at least 100 bytes of memory.
An edge takes up at least 400 bytes of memory.
(A Perl scalar value takes 16 bytes, or 12 bytes if it's a reference.)
These size approximations are very approximate and optimistic (they are based on
total_size() of Devel::Size). In real life many factors affect these numbers, for example
how Perl is configured. The numbers are for a 32-bit platform and for Perl 5.8.8.
Roughly, the above numbers mean that in a megabyte of memory you can fit for example a
graph of about 1000 vertices and about 2500 edges.
Hyperedges, hypervertices, hypergraphs
BEWARE: this is a rather thinly tested feature, and the theory is even less so. Do not
expect this to stay as it is (or at all) in future releases.
NOTE: most usual graph algorithms (and basic concepts) break horribly (or at least will
look funny) with these hyperthingies. Caveat emptor.
Hyperedges are edges that connect a number of vertices different from the usual two.
Hypervertices are vertices that consist of a number of vertices different from the usual
one.
Note that for hypervertices there is an asymmetry: when adding hypervertices, the single
vertices are also implicitly added.
Hypergraphs are graphs with hyperedges.
To enable hyperness when constructing Graphs use the "hyperedged" and "hypervertexed"
attributes:
my $h = Graph->new(hyperedged => 1, hypervertexed => 1);
To add hypervertexes, either explicitly use more than one vertex (or, indeed, no vertices)
when using add_vertex()
$h->add_vertex("a", "b")
$h->add_vertex()
or implicitly with array references when using add_edge()
$h->add_edge(["a", "b"], "c")
$h->add_edge()
Testing for existence and deletion of hypervertices and hyperedges works similarly.
To test for hyperness of a graph use the
is_hypervertexed
hypervertexed
$g->is_hypervertexed
$g->hypervertexed
is_hyperedged
hyperedged
$g->is_hyperedged
$g->hyperedged
Since hypervertices consist of more than one vertex:
vertices_at
$g->vertices_at($v)
Return the vertices at the vertex. This may return just the vertex or also other
vertices.
To go with the concept of undirected in normal (non-hyper) graphs, there is a similar
concept of omnidirected (this is my own coinage, "all-directions") for hypergraphs, and
you can naturally test for it by
is_omnidirected
omnidirected
is_omniedged
omniedged
$g->is_omniedged
$g->omniedged
$g->is_omnidirected
$g->omnidirected
Return true if the graph is omnidirected (edges have no direction), false if not.
You may be wondering why on earth did I make up this new concept, why didn't the
"undirected" work for me? Well, because of this:
$g = Graph->new(hypervertexed => 1, omnivertexed => 1);
That's right, vertices can be omni, too - and that is indeed the default. You can turn it
off and then $g->add_vertex(qw(a b)) no more means adding also the (hyper)vertex qw(b a).
In other words, the "directivity" is orthogonal to (or independent of) the number of
vertices in the vertex/edge.
is_omnivertexed
omnivertexed
Another oddity that fell out of the implementation is the uniqueness attribute, that comes
naturally in "uniqedged" and "uniqvertexed" flavours. It does what it sounds like, to
unique or not the vertices participating in edges and vertices (is the hypervertex qw(a b
a) the same as the hypervertex qw(a b), for example). Without too much explanation:
is_uniqedged
uniqedged
is_uniqvertexed
uniqvertexed
Backward compatibility with Graph 0.2
The Graph 0.2 (and 0.2xxxx) had the following features
• vertices() always sorted the vertex list, which most of the time is unnecessary and
wastes CPU.
• edges() returned a flat list where the begin and end vertices of the edges were
intermingled: every even index had an edge begin vertex, and every odd index had an
edge end vertex. This had the unfortunate consequence of "scalar(@e = edges)" being
twice the number of edges, and complicating any algorithm walking through the edges.
• The vertex list returned by edges() was sorted, the primary key being the edge begin
vertices, and the secondary key being the edge end vertices.
• The attribute API was oddly position dependent and dependent on the number of
arguments. Use ..._graph_attribute(), ..._vertex_attribute(), ..._edge_attribute()
instead.
In future releases of Graph (any release after 0.50) the 0.2xxxx compatibility will be
removed. Upgrade your code now.
If you want to continue using these (mis)features you can use the "compat02" flag when
creating a graph:
my $g = Graph->new(compat02 => 1);
This will change the vertices() and edges() appropriately. This, however, is not
recommended, since it complicates all the code using vertices() and edges(). Instead it
is recommended that the vertices02() and edges02() methods are used. The corresponding
new style (unsorted, and edges() returning a list of references) methods are called
vertices05() and edges05().
To test whether a graph has the compatibility turned on
is_compat02
compat02
$g->is_compat02
$g->compat02
The following are not backward compatibility methods, strictly speaking, because they did
not exist before.
edges02
Return the edges as a flat list of vertices, elements at even indices being the start
vertices and elements at odd indices being the end vertices.
edges05
Return the edges as a list of array references, each element containing the vertices
of each edge. (This is not a backward compatibility interface as such since it did
not exist before.)
vertices02
Return the vertices in sorted order.
vertices05
Return the vertices in random order.
For the attributes the recommended way is to use the new API.
Do not expect new methods to work for compat02 graphs.
The following compatibility methods exist:
has_attribute
has_attributes
get_attribute
get_attributes
set_attribute
set_attributes
delete_attribute
delete_attributes
Do not use the above, use the new attribute interfaces instead.
vertices_unsorted
Alias for vertices() (or rather, vertices05()) since the vertices() now always returns
the vertices in an unsorted order. You can also use the unsorted_vertices import, but
only with a true value (false values will cause an error).
density_limits
my ($sparse, $dense, $complete) = $g->density_limits;
Return the "density limits" used to classify graphs as "sparse" or "dense". The first
limit is C/4 and the second limit is 3C/4, where C is the number of edges in a
complete graph (the last "limit").
density
my $density = $g->density;
Return the density of the graph, the ratio of the number of edges to the number of
edges in a complete graph.
vertex
my $v = $g->vertex($v);
Return the vertex if the graph has the vertex, undef otherwise.
out_edges
in_edges
edges($v)
This is now called edges_at($v).
DIAGNOSTICS
• Graph::...Map...: arguments X expected Y ...
If you see these (more user-friendly error messages should have been triggered above
and before these) please report any such occurrences, but in general you should be
happy to see these since it means that an attempt to call something with a wrong
number of arguments was caught in time.
• Graph::add_edge: graph is not hyperedged ...
Maybe you used add_weighted_edge() with only the two vertex arguments.
• Not an ARRAY reference at lib/Graph.pm ...
One possibility is that you have code based on Graph 0.2xxxx that assumes Graphs being
blessed hash references, possibly also assuming that certain hash keys are available
to use for your own purposes. In Graph 0.50 none of this is true. Please do not
expect any particular internal implementation of Graphs. Use inheritance and
graph/vertex/edge attributes instead.
Another possibility is that you meant to have objects (blessed references) as graph
vertices, but forgot to use "refvertexed" (see "refvertexed") when creating the graph.
ACKNOWLEDGEMENTS
All bad terminology, bugs, and inefficiencies are naturally mine, all mine, and not the
fault of the below.
Thanks to Nathan Goodman and Andras Salamon for bravely betatesting my pre-0.50 code. If
they missed something, that was only because of my fiendish code.
The following literature for algorithms and some test cases:
• Algorithms in C, Third Edition, Part 5, Graph Algorithms, Robert Sedgewick, Addison
Wesley
• Introduction to Algorithms, First Edition, Cormen-Leiserson-Rivest, McGraw Hill
• Graphs, Networks and Algorithms, Dieter Jungnickel, Springer
SEE ALSO
Persistent/Serialized graphs? You want to read/write Graphs? See the Graph::Reader and
Graph::Writer in CPAN.
AUTHOR AND COPYRIGHT
Jarkko Hietaniemi jhi@iki.fi
COPYRIGHT
Copyright (c) 1998-2013 Jarkko Hietaniemi. All rights reserved.
LICENSE
This program is free software; you can redistribute it and/or modify it under the same
terms as Perl 5 itself.