NAME
::struct::graph - Create and manipulate directed graph
objects
SYNOPSIS
package require struct ?1.0?
::struct::graph graphName
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DESCRIPTION
The ::struct::graph command creates a new graph object
with an associated global Tcl command whose name is graph
Name. This command may be used to invoke various opera
tions on the graph. It has the following general form:
graphName option ?arg arg ...?
Option and the args determine the exact behavior of the
command.
A directed graph is a structure containing two collections
of elements, called nodes and arcs resp., together with a
relation ("connectivity") that places a general structure
upon the nodes and arcs.
Each arc is connected to two nodes, one of which is called
the source and the other the target. This imposes a direc
tion upon the arc, which is said to go from the source to
the target. It is allowed that source and target of an arc
are the same node. Such an arc is called a loop. Whenever
a node is source or target of an arc both are said to be
adjacent. This extends into a relation between nodes, i.e.
if two nodes are connected through at least one arc they
are said to be adjacent too.
Each node can be the source and target for any number of
arcs. The former are called the outgoing arcs of the node,
the latter the incoming arcs of the node. The number of
edges in either set is called the in- resp. the out-degree
of the node.
In addition to maintaining the node and arc relationships,
this graph implementation allows any number of keyed val
ues to be associated with each node and arc.
The following commands are possible for graph objects:
graphName destroy
Destroy the graph, including its storage space and
associated command.
Remove the specified arcs from the graph.
graphName arc exists arc
Return true if the specified arc exists in the
graph.
graphName arc get arc ?-key key?
Return the value associated with the key key for
the arc. If no key is specified, the key data is
assumed.
graphName arc insert start end ?child?
Insert an arc named child into the graph beginning
at the node start and ending at the node end. If
the name of the new arc is not specified the system
will generate a unique name of the form arcx.
graphName arc set arc ?-key key? ?value?
Set or get one of the keyed values associated with
an arc. If no key is specified, the key data is
assumed. Each arc that is added to a graph has the
value "" assigned to the key data automatically.
An arc may have any number of keyed values associ
ated with it. If value is not specified, this com
mand returns the current value assigned to the key;
if value is specified, this command assigns that
value to the key.
graphName arc source arc
Return the node the given arc begins at.
graphName arc target arc
Return the node the given arc ends at.
graphName arc unset arc ?-key key?
Remove a keyed value from the arc arc. If no key
is specified, the key data is assumed.
graphName arcs ?-in|-out|-adj|-inner|-embedding nodelist?
Return a list of arcs in the graph. If no restric
tion is specified a list containing all arcs is
returned. If one of the five possible restrictions
is specified only arcs satisfying that restriction
are returned. All restrictions involve a list of
nodes, specified after the key for the restriction
itself.
-in Return a list of all arcs whose target is one
of the nodes in the nodelist.
-out Return a list of all arcs whose source is one
of the nodes in the nodelist.
one of the nodes in the nodelist. This is the union
of the nodes returned by -in and -out.
-inner Return a list of all arcs adjacent to two of
the nodes in the nodelist. This is the set of arcs
in the subgraph spawned by the specified nodes.
-embedding Return a list of all arcs adjacent to
exactly one of the nodes in the nodelist. This is
the set of arcs connecting the subgraph spawned by
the specified nodes to the rest of the graph.
graphName node degree ?-in|-out? node
Return the number of arcs adjacent to the specified
node. If one of the restrictions -in or -out is
given only the incoming resp. outgoing arcs are
counted.
graphName node delete node ?node ...?
Remove the specified nodes from the graph. All of
the nodes' arcs will be removed as well to prevent
unconnected arcs.
graphName node exists node
Return true if the specified node exists in the
graph.
graphName node get node ?-key key?
Return the value associated with the key key for
the node. If no key is specified, the key data is
assumed.
graphName node insert ?child?
Insert a node named child into the graph. The nodes
has no arcs connected to it. If the name of the new
child is not specified the system will generate a
unique name of the form nodex.
graphName node opposite node arc
Return the node at the other end of the specified
arc, which has to be adjacent to the given node.
graphName node set node ?-key key? ?value?
Set or get one of the keyed values associated with
a node. If no key is specified, the key data is
assumed. Each node that is added to a graph has
the value "" assigned to the key data automati
cally. A node may have any number of keyed values
associated with it. If value is not specified,
this command returns the current value assigned to
the key; if value is specified, this command
assigns that value to the key.
Remove a keyed value from the node node. If no key
is specified, the key data is assumed.
graphName nodes ?-in|-out|-adj|-inner|-embedding nodelist?
Return a list of nodes in the graph. If no restric
tion is specified a list containing all nodes is
returned. If one of the five possible restrictions
is specified only nodes satisfying that restriction
are returned. All restrictions involve a list of
nodes, specified after the key for the restriction
itself.
The possible restrictions are the same as for
method arcs. The set of nodes to return is computed
as the union of all source and target nodes for all
the arcs satisfying the restriction as defined for
arcs.
graphName swap node1 node2
Swap the position of node1 and node2 in the graph.
graphName walk node ?-order order? ?-type type? ?-dir
direction? -command cmd
Perform a breadth-first or depth-first walk of the
graph starting at the node node going in either the
direction of outgoing or opposite to the incoming
arcs.
The type of walk, breadth-first or depth-first, is
determined by the value of type; bfs indicates
breadth-first, dfs indicates depth-first. Depth-
first is the default.
The order of the walk, pre-order, post-order or
both-order is determined by the value of order; pre
indicates pre-order, post indicates post-order,
both indicates both-order. Pre-order is the
default. Pre-order walking means that a node is
visited before any of its neighbors (as defined by
the direction, see below). Post-order walking means
that a parent is visited after any of its neigh
bors. Both-order walking means that a node is vis
ited before and after any of its neighbors. The
combination of a bread-first walk with post- or
both-order is illegal.
The direction of the walk is determined by the
value of dir; backward indicates the direction
opposite to the incoming arcs, forward indicates
the direction of the outgoing arcs.
As the walk progresses, the command cmd will be
(enter or leave) and values graphName and the name
of the current node appended. For a pre-order walk
all nodes are Bentered, for a post-order all nodes
are left. In a both-order walk the first visit of a
node enters it, the second visit leaves it.
KEYWORDS
graph
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