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struct::graph(n)	      Tcl Data Structures	      struct::graph(n)

______________________________________________________________________________

NAME
       struct::graph - Create and manipulate directed graph objects

SYNOPSIS
       package require Tcl  8.4

       package require struct::graph  ?2.4?

       package require struct::list  ?1.5?

       package require struct::set  ?2.2.3?

       ::struct::graph ?graphName? ?=|:=|as|deserialize source?

       graphName option ?arg arg ...?

       graphName = sourcegraph

       graphName --> destgraph

       graphName append key value

       graphName deserialize serialization

       graphName destroy

       graphName arc append arc key value

       graphName arc attr key

       graphName arc attr key -arcs list

       graphName arc attr key -glob globpattern

       graphName arc attr key -regexp repattern

       graphName arc delete arc ?arc ...?

       graphName arc exists arc

       graphName arc flip arc

       graphName arc get arc key

       graphName arc getall arc ?pattern?

       graphName arc getunweighted

       graphName arc getweight arc

       graphName arc keys arc ?pattern?

       graphName arc keyexists arc key

       graphName arc insert start end ?child?

       graphName arc lappend arc key value

       graphName arc rename arc newname

       graphName arc set arc key ?value?

       graphName arc setunweighted ?weight?

       graphName arc setweight arc weight

       graphName arc unsetweight arc

       graphName arc hasweight arc

       graphName arc source arc

       graphName arc target arc

       graphName arc nodes arc

       graphName arc move-source arc newsource

       graphName arc move-target arc newtarget

       graphName arc move arc newsource newtarget

       graphName arc unset arc key

       graphName arc weights

       graphName   arcs	  ?-key	  key?	 ?-value  value?  ?-filter  cmdprefix?
       ?-in|-out|-adj|-inner|-embedding node node...?

       graphName lappend key value

       graphName node append node key value

       graphName node attr key

       graphName node attr key -nodes list

       graphName node attr key -glob globpattern

       graphName node attr key -regexp repattern

       graphName node degree ?-in|-out? node

       graphName node delete node ?node...?

       graphName node exists node

       graphName node get node key

       graphName node getall node ?pattern?

       graphName node keys node ?pattern?

       graphName node keyexists node key

       graphName node insert ?node...?

       graphName node lappend node key value

       graphName node opposite node arc

       graphName node rename node newname

       graphName node set node key ?value?

       graphName node unset node key

       graphName  nodes	 ?-key	key?  ?-value	value?	 ?-filter   cmdprefix?
       ?-in|-out|-adj|-inner|-embedding node node...?

       graphName get key

       graphName getall ?pattern?

       graphName keys ?pattern?

       graphName keyexists key

       graphName serialize ?node...?

       graphName set key ?value?

       graphName swap node1 node2

       graphName unset key

       graphName  walk node ?-order order? ?-type type? ?-dir direction? -com‐
       mand cmd

_________________________________________________________________

DESCRIPTION
       A directed graph is a structure containing two collections of elements,
       called  nodes and arcs respectively, together with a relation ("connec‐
       tivity") 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 direction 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 either the 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	 adja‐
       cent too.

       Each node can be the source and target for any number of arcs. The for‐
       mer are called the outgoing arcs of the node, the latter	 the  incoming
       arcs  of	 the  node. The number of arcs in either set is called the in-
       degree resp. the out-degree of the node.

       In addition to maintaining the node and arc relationships,  this	 graph
       implementation  allows  any number of named attributes to be associated
       with the graph itself, and each node or arc.

       Note: The major version of the package struct has been changed to  ver‐
       sion  2.0, due to backward incompatible changes in the API of this mod‐
       ule. Please read the section Changes for 2.0 for a  full	 list  of  all
       changes, incompatible and otherwise.

       Note:  A	 C-implementation  of the command can be had from the location
       http://www.purl.org/NET/schlenker/tcl/cgraph.	     See	  also
       http://wiki.tcl.tk/cgraph.   This implementation uses a bit less memory
       than the tcl version provided here directly, and is faster. Its support
       is limited to versions of the package before 2.0.

       As  of  version	2.2 of this package a critcl based C implementation is
       available from here as well. This implementation however	 requires  Tcl
       8.4 to run.

       The main command of the package is:

       ::struct::graph ?graphName? ?=|:=|as|deserialize source?
	      The command creates a new graph object with an associated global
	      Tcl command whose name is graphName.  This command may  be  used
	      to invoke various operations on the graph.  It has the following
	      general form:

	      graphName option ?arg arg ...?
		     Option and the args determine the exact behavior  of  the
		     command.

       If  graphName  is  not specified a unique name will be generated by the
       package itself. If a source is specified the new graph will be initial‐
       ized  to	 it.  For  the	operators =, :=, and as the source argument is
       interpreted as the name of another graph	 object,  and  the  assignment
       operator = will be executed. For the operator deserialize the source is
       a serialized graph object and deserialize will be executed.

       In other words

	   ::struct::graph mygraph = b

       is equivalent to

	   ::struct::graph mygraph
	   mygraph = b

       and

	   ::struct::graph mygraph deserialize $b

       is equivalent to

	   ::struct::graph mygraph
	   mygraph deserialize $b

       The following commands are possible for graph objects:

       graphName = sourcegraph
	      This is the assignment operator for graph objects. It copies the
	      graph  contained	in the graph object sourcegraph over the graph
	      data in graphName. The old contents of graphName are deleted  by
	      this operation.

	      This operation is in effect equivalent to

		  graphName deserialize [sourcegraph serialize]

	      The  operation  assumes that the sourcegraph provides the method
	      serialize and that this method returns a valid graph  serializa‐
	      tion.

       graphName --> destgraph
	      This  is	the  reverse assignment operator for graph objects. It
	      copies the graph contained in the graph  object  graphName  over
	      the  graph  data	in  the object destgraph.  The old contents of
	      destgraph are deleted by this operation.

	      This operation is in effect equivalent to

		  destgraph deserialize [graphName serialize]

	      The operation assumes that the  destgraph	 provides  the	method
	      deserialize and that this method takes a graph serialization.

       graphName append key value
	      Appends  a  value to one of the keyed values associated with the
	      graph.  Returns the new value given to the attribute key.

       graphName deserialize serialization
	      This is the complement to serialize. It replaces the graph  data
	      in  graphName  with  the	graph  described  by the serialization
	      value. The old contents of graphName are deleted by this	opera‐
	      tion.

       graphName destroy
	      Destroys	the  graph, including its storage space and associated
	      command.

       graphName arc append arc key value
	      Appends a value to one of the keyed values  associated  with  an
	      arc. Returns the new value given to the attribute key.

       graphName arc attr key

       graphName arc attr key -arcs list

       graphName arc attr key -glob globpattern

       graphName arc attr key -regexp repattern
	      This  method retrieves the value of the attribute named key, for
	      all arcs in the graph (matching the  restriction	specified  via
	      one of the possible options) and having the specified attribute.

	      The  result  is a dictionary mapping from arc names to the value
	      of attribute key at that arc.  Arcs  not	having	the  attribute
	      key,  or	not passing a specified restriction, are not listed in
	      the result.

	      The possible restrictions are:

	      -arcs  The value is a list of arcs. Only the arcs	 mentioned  in
		     this list are searched for the attribute.

	      -glob  The  value	 is a glob pattern. Only the arcs in the graph
		     whose names match	this  pattern  are  searched  for  the
		     attribute.

	      -regexp
		     The  value	 is a regular expression. Only the arcs in the
		     graph whose names match this pattern are searched for the
		     attribute.

       graphName arc delete arc ?arc ...?
	      Remove the specified arcs from the graph.

       graphName arc exists arc
	      Return true if the specified arc exists in the graph.

       graphName arc flip arc
	      Reverses	the  direction	of  the named arc, i.e. the source and
	      target nodes of the arc are exchanged with each other.

       graphName arc get arc key
	      Returns the value associated with the key key for the arc.

       graphName arc getall arc ?pattern?
	      Returns a dictionary (suitable for use with [array set]) for the
	      arc.   If	 the  pattern  is  specified only the attributes whose
	      names match the pattern will be part of the returned dictionary.
	      The pattern is a glob pattern.

       graphName arc getunweighted
	      Returns  a  list	containing  the names of all arcs in the graph
	      which have no weight associated with them.

       graphName arc getweight arc
	      Returns the weight associated with the arc. Throws an  error  if
	      the arc has no weight associated with it.

       graphName arc keys arc ?pattern?
	      Returns a list of keys for the arc.  If the pattern is specified
	      only the attributes whose names match the pattern will  be  part
	      of the returned list. The pattern is a glob pattern.

       graphName arc keyexists arc key
	      Return true if the specified key exists for the arc.

       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 lappend arc key value
	      Appends a value (as a list) to one of the keyed  values  associ‐
	      ated  with  an arc. Returns the new value given to the attribute
	      key.

       graphName arc rename arc newname
	      Renames the arc arc to newname. An error is thrown if either the
	      arc  does	 not exist, or a arc with name newname does exist. The
	      result of the command is the new name of the arc.

       graphName arc set arc key ?value?
	      Set or get one of the keyed values associated with an  arc.   An
	      arc  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, and returns that value.

       graphName arc setunweighted ?weight?
	      Sets the weight of all arcs without a weight to weight.  Returns
	      the  empty  string as its result. If not present weight defaults
	      to 0.

       graphName arc setweight arc weight
	      Sets the weight of the arc to weight. Returns weight.

       graphName arc unsetweight arc
	      Removes the weight of the arc, if present. Does  nothing	other‐
	      wise. Returns the empty string.

       graphName arc hasweight arc
	      Determines  if  the  arc	has  a weight associated with it.  The
	      result is a boolean value, True if  a  weight  is	 defined,  and
	      False otherwise.

       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 nodes arc
	      Return the nodes the given arc begins and ends at, as a two-ele‐
	      ment list.

       graphName arc move-source arc newsource
	      Changes the source node of the arc to newsource. It can be  said
	      that the arc rotates around its target node.

       graphName arc move-target arc newtarget
	      Changes  the target node of the arc to newtarget. It can be said
	      that the arc rotates around its source node.

       graphName arc move arc newsource newtarget
	      Changes both source and target nodes of the  arc	to  newsource,
	      and newtarget resp.

       graphName arc unset arc key
	      Remove  a keyed value from the arc arc. The method will do noth‐
	      ing if the key does not exist.

       graphName arc weights
	      Returns a dictionary whose keys are the names of all arcs	 which
	      have  a  weight  associated  with them, and the values are these
	      weights.

       graphName  arcs	?-key  key?   ?-value	value?	 ?-filter   cmdprefix?
       ?-in|-out|-adj|-inner|-embedding node node...?
	      Returns a list of arcs in the graph. If no restriction is speci‐
	      fied a list containing all arcs is  returned.  Restrictions  can
	      limit the list of returned arcs based on the nodes that are con‐
	      nected by the arc, on the keyed values associated with the  arc,
	      or  both.	 A  general  filter  command  can be used as well. The
	      restrictions that involve connected nodes take a variable number
	      of  nodes	 as argument, specified after the name of the restric‐
	      tion itself.

	      The restrictions imposed by either -in, -out, -adj,  -inner,  or
	      -embedded are applied first. Specifying more than one of them is
	      illegal.

	      After that the  restrictions  set	 via  -key  (and  -value)  are
	      applied.	Specifying more than one -key (and -value) is illegal.
	      Specifying -value alone, without -key is illegal as well.

	      Any restriction set through -filter is applied last.  Specifying
	      more than one -filter is illegal.

	      Coming  back  to	the  restrictions based on a set of nodes, the
	      command recognizes the following switches:

	      -in    Return a list of all arcs whose  target  is  one  of  the
		     nodes  in the set of nodes. I.e. it computes the union of
		     all incoming arcs of the nodes in the set.

	      -out   Return a list of all arcs whose  source  is  one  of  the
		     nodes  in the set of nodes. I.e. it computes the union of
		     all outgoing arcs of the nodes in the set.

	      -adj   Return a list of all arcs adjacent to at least one of the
		     nodes in the set. This is the union of the nodes returned
		     by -in and -out.

	      -inner Return a list of all arcs which are adjacent  to  two  of
		     the nodes in the set. This is the set of arcs in the sub‐
		     graph spawned by the specified nodes.

	      -embedding
		     Return a list of all arcs adjacent to exactly one of  the
		     nodes  in the set. This is the set of arcs connecting the
		     subgraph spawned by the specified nodes to	 the  rest  of
		     the graph.

	      -key key
		     Limit  the	 list  of arcs that are returned to those arcs
		     that have an associated key key.

	      -value value
		     This restriction can only be  used	 in  combination  with
		     -key.  It	limits	the  list of arcs that are returned to
		     those arcs whose associated key key has the value value.

	      -filter cmdrefix
		     Limit the list of arcs that are returned  to  those  arcs
		     that  pass	 the  test. The command in cmdprefix is called
		     with two arguments, the name of the graph object, and the
		     name  of  the arc in question. It is executed in the con‐
		     text of the caller and has to  return  a  boolean	value.
		     Arcs for which the command returns false are removed from
		     the result list before it is returned to the caller.

       graphName lappend key value
	      Appends a value (as a list) to one of the keyed  values  associ‐
	      ated  with  the  graph.  Returns	the  new  value	 given	to the
	      attribute key.

       graphName node append node key value
	      Appends a value to one of the keyed values  associated  with  an
	      node. Returns the new value given to the attribute key.

       graphName node attr key

       graphName node attr key -nodes list

       graphName node attr key -glob globpattern

       graphName node attr key -regexp repattern
	      This  method retrieves the value of the attribute named key, for
	      all nodes in the graph (matching the restriction	specified  via
	      one of the possible options) and having the specified attribute.

	      The  result is a dictionary mapping from node names to the value
	      of attribute key at that node.  Nodes not having	the  attribute
	      key,  or	not passing a specified restriction, are not listed in
	      the result.

	      The possible restrictions are:

	      -nodes The value is a list of nodes. Only the nodes mentioned in
		     this list are searched for the attribute.

	      -glob  The  value is a glob pattern. Only the nodes in the graph
		     whose names match	this  pattern  are  searched  for  the
		     attribute.

	      -regexp
		     The  value is a regular expression. Only the nodes in the
		     graph whose names match this pattern are searched for the
		     attribute.

       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
	      Return the value associated with the key key for the node.

       graphName node getall node ?pattern?
	      Returns a dictionary (suitable for use with [array set]) for the
	      node.   If  the  pattern	is specified only the attributes whose
	      names match the pattern will be part of the returned dictionary.
	      The pattern is a glob pattern.

       graphName node keys node ?pattern?
	      Returns  a  list of keys for the node.  If the pattern is speci‐
	      fied only the attributes whose names match the pattern  will  be
	      part of the returned list. The pattern is a glob pattern.

       graphName node keyexists node key
	      Return true if the specified key exists for the node.

       graphName node insert ?node...?
	      Insert  one  or more nodes into the graph. The new nodes have no
	      arcs connected to them. If no node is specified one node will be
	      inserted, and the system will generate a unique name of the form
	      nodex for it.

       graphName node lappend node key value
	      Appends a value (as a list) to one of the keyed  values  associ‐
	      ated  with an node. Returns the new value given to the attribute
	      key.

       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 rename node newname
	      Renames  the  node node to newname. An error is thrown if either
	      the node does not exist, or a node with name newname does exist.
	      The result of the command is the new name of the node.

       graphName node set node key ?value?
	      Set  or  get  one	 of the keyed values associated with a node. 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.

       graphName node unset node key
	      Remove  a	 keyed	value  from  the node node. The method will do
	      nothing if the key does not exist.

       graphName  nodes	 ?-key	key?  ?-value	value?	 ?-filter   cmdprefix?
       ?-in|-out|-adj|-inner|-embedding node node...?
	      Return  a list of nodes in the graph. Restrictions can limit the
	      list of returned nodes based on neighboring nodes, or  based  on
	      the keyed values associated with the node. The restrictions that
	      involve neighboring nodes have a	list  of  nodes	 as  argument,
	      specified after the name of the restriction itself.

	      The  possible  restrictions are the same as for method arcs. The
	      exact meanings change slightly, as they operate on nodes instead
	      of arcs. The command recognizes:

	      -in    Return a list of all nodes with at least one outgoing arc
		     ending in a node found in the  specified  set  of	nodes.
		     Alternatively  specified  as  the set of source nodes for
		     the -in arcs of the node set. The incoming neighbours.

	      -out   Return a list of all nodes with at least one incoming arc
		     starting  in  a node found in the specified set of nodes.
		     Alternatively specified as the set of  target  nodes  for
		     the -out arcs of the node set. The outgoing neighbours.

	      -adj   This  is the union of the nodes returned by -in and -out.
		     The neighbours.

	      -inner The set of neighbours (see -adj above) which are also  in
		     the  set  of nodes. I.e. the intersection between the set
		     of nodes and the neighbours per -adj.

	      -embedding
		     The set of neighbours (see -adj above) which are  not  in
		     the  set of nodes. I.e. the difference between the neigh‐
		     bours as per -adj, and the set of nodes.

	      -key key
		     Limit the list of nodes that are returned to those	 nodes
		     that have an associated key key.

	      -value value
		     This  restriction	can  only  be used in combination with
		     -key. It limits the list of nodes that  are  returned  to
		     those nodes whose associated key key has the value value.

	      -filter cmdrefix
		     Limit  the list of nodes that are returned to those nodes
		     that pass the test. The command in	 cmdprefix  is	called
		     with two arguments, the name of the graph object, and the
		     name of the node in question. It is executed in the  con‐
		     text  of  the  caller  and has to return a boolean value.
		     Nodes for which the command  returns  false  are  removed
		     from the result list before it is returned to the caller.

       graphName get key
	      Return the value associated with the key key for the graph.

       graphName getall ?pattern?
	      Returns a dictionary (suitable for use with [array set]) for the
	      whole graph.  If the pattern is specified	 only  the  attributes
	      whose  names match the pattern will be part of the returned dic‐
	      tionary. The pattern is a glob pattern.

       graphName keys ?pattern?
	      Returns a list of keys for the whole graph.  If the  pattern  is
	      specified only the attributes whose names match the pattern will
	      be part of the returned list. The pattern is a glob pattern.

       graphName keyexists key
	      Return true if the specified key exists for the whole graph.

       graphName serialize ?node...?
	      This method serializes the sub-graph spanned up by the nodes. In
	      other  words  it	returns a tcl value completely describing that
	      graph. If no nodes are specified the whole graph will be serial‐
	      ized.   This  allows, for example, the transfer of graph objects
	      (or parts thereof) over arbitrary	 channels,  persistence,  etc.
	      This  method is also the basis for both the copy constructor and
	      the assignment operator.

	      The result of this method has to be semantically identical  over
	      all  implementations  of	the graph interface. This is what will
	      enable us to copy graph data between  different  implementations
	      of the same interface.

	      The  result is a list containing a multiple of three items, plus
	      one!  In other words, '[llength $serial] % 3 == 1'. Valid values
	      include 1, 4, 7, ...

	      The  last	 element  of  the  list is a dictionary containing the
	      attributes associated with the whole graph.  Regarding the other
	      elements; each triple consists of

	      [1]    The name of the node to be described,

	      [2]    A	dictionary  containing	the attributes associated with
		     the node,

	      [3]    And a list describing all the arcs starting at that node.

       The elements of the arc list are lists containing three	or  four  ele‐
       ments each, i.e.

	      [1]    The name of the arc described by the element,

	      [2]    A reference to the destination node of the arc. This ref‐
		     erence is an integer number given the index of that  node
		     in	 the  main  serialization  list. As that it is greater
		     than or equal to zero, less than the length of the	 seri‐
		     alization,	 and  a multiple of three.  Note: For internal
		     consistency no arc name may be used twice, whether in the
		     same  node,  or at some other node. This is a global con‐
		     sistency requirement for the serialization.

	      [3]    And a dictionary  containing  the	attributes  associated
		     with the arc.

	      [4]    The  weight  associated  with  the	 arc.  This  value  is
		     optional. Its non-presence means that the arc in question
		     has no weight associated with it.

		     Note: This information is new, compared to the serializa‐
		     tion of graph 2.3 and earlier. By making it  an  optional
		     element  the  new format is maximally compatible with the
		     old. This means that any graph  not  using	 weights  will
		     generate a serialization which is still understood by the
		     older graph package. A serialization will not  be	under‐
		     stood  any	 longer	 by the older packages if, and only if
		     the graph it was generated from actually  has  arcs  with
		     weights.

       For  all	 attribute  dictionaries  they	keys  are  the	names  of  the
       attributes, and the values are the values for each name.

       Note: The order of the nodes in the serialization has no relevance, nor
       has the order of the arcs per node.

	   # A possible serialization for the graph structure
	   #
	   #	    d -----> %2
	   #	   /	     ^ \\
	   #	  /	    /	\\
	   #	 /	   b	 \\
	   #	/	  /	  \\
	   #  %1 <- a - %0	   e
	   #	^	  \\	  /
	   #	 \\	   c	 /
	   #	  \\	    \\	/
	   #	   \\	     v v
	   #	    f ------ %3
	   # is
	   #
	   # %3 {} {{f 6 {}}} %0 {} {{a 6 {}} {b 9 {}} {c 0 {}}} %1 {} {{d 9 {}}} %2 {} {{e 0 {}}} {}
	   #
	   # This assumes that the graph has neither attribute data nor weighted arcs.

       graphName set key ?value?
	      Set  or  get  one of the keyed values associated with a graph. A
	      graph 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.

       graphName swap node1 node2
	      Swap the position of node1 and node2 in the graph.

       graphName unset key
	      Remove  a keyed value from the graph. The method will do nothing
	      if the key does not exist.

       graphName walk node ?-order order? ?-type type? ?-dir direction?	 -com‐
       mand cmd
	      Perform  a breadth-first or depth-first walk of the graph start‐
	      ing 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  neighbors. Both-order walking means that a node is
	      visited before and after any of its neighbors.  The  combination
	      of a breadth-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 evaluated at
	      each node, with the mode of the call (enter or leave) and values
	      graphName	 and the name of the current node appended. For a pre-
	      order walk, all nodes are entered, 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.

CHANGES FOR 2.0
       The following noteworthy changes have occurred:

       [1]    The API for accessing attributes and their values has been  sim‐
	      plified.

	      All  functionality  regarding  the  default attribute "data" has
	      been removed. This default attribute does not exist anymore. All
	      accesses to attributes have to specify the name of the attribute
	      in question. This backward incompatible  change  allowed	us  to
	      simplify the signature of all methods handling attributes.

	      Especially the flag -key is not required anymore, even more, its
	      use is now forbidden. Please read the documentation for the  arc
	      and  node	 methods  set,	get,  getall,  unset, append, lappend,
	      keyexists and keys for a description of the new API's.

       [2]    The methods keys and getall now take an optional	pattern	 argu‐
	      ment  and will return only attribute data for keys matching this
	      pattern.

       [3]    Arcs and nodes can now be renamed. See the documentation for the
	      methods arc rename and node rename.

       [4]    The structure has been extended with API's for the serialization
	      and deserialization of graph objects, and a number of operations
	      based on them (graph assignment, copy construction).

	      Please read the documentation for the methods serialize, deseri‐
	      alize, =, and -->, and the documentation on the construction  of
	      graph objects.

	      Beyond  the  copying of whole graph objects these new API's also
	      enable the transfer of graph objects over arbitrary channels and
	      for easy persistence.

       [5]    A	 new method, attr, was added to both arc and node allowing the
	      query and retrieval of attribute data without regard to arc  and
	      node relationships.

       [6]    Both  methods arcs and nodes have been extended with the ability
	      to select arcs and nodes based on an  arbitrary  filtering  cri‐
	      terium.

BUGS, IDEAS, FEEDBACK
       This  document,	and the package it describes, will undoubtedly contain
       bugs and other problems.	 Please report such in the category struct  ::
       graph	 of	the	Tcllib	   SF	  Trackers     [http://source‐
       forge.net/tracker/?group_id=12883].  Please also report any  ideas  for
       enhancements you may have for either package and/or documentation.

KEYWORDS
       adjacent,  arc,	cgraph,	 degree,  edge,	 graph, loop, neighbour, node,
       serialization, subgraph, vertex

CATEGORY
       Data structures

COPYRIGHT
       Copyright (c) 2002-2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>

struct				      2.4		      struct::graph(n)
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