graphElements.h File Reference

some utils for topology : NodeId, Edge, Arc and consorts ... More...

#include <iostream>
#include <agrum/agrum.h>
#include <agrum/base/core/set.h>
#include <agrum/base/graphs/graphElements_inl.h>

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Classes
class	gum::Edge
	The base class for all undirected edges. More...
class	gum::Arc
	The base class for all directed edges. More...

Namespaces
namespace	gum
	gum is the global namespace for all aGrUM entities

Typedefs
using	gum::NodeId = Size
	Type for node ids.
template<class VAL>
using	gum::NodeProperty = HashTable< NodeId, VAL >
	Property on graph elements.
template<class VAL>
using	gum::EdgeProperty = HashTable< Edge, VAL >
	Property on graph elements.
template<class VAL>
using	gum::ArcProperty = HashTable< Arc, VAL >
	Property on graph elements.

Functions
std::ostream &	gum::operator<< (std::ostream &stream, const Edge &edge)
	to friendly display an edge
std::ostream &	gum::operator<< (std::ostream &stream, const Arc &arc)
	to friendly display an arc
using	gum::EdgeSet = Set< Edge >
	Some typdefs and define for shortcuts ...
using	gum::NodeSet = Set< NodeId >
	Some typdefs and define for shortcuts ...
using	gum::ArcSet = Set< Arc >
	Some typdefs and define for shortcuts ...
using	gum::ArcSetIterator = ArcSet::const_iterator
	Some typdefs and define for shortcuts ...
using	gum::EdgeSetIterator = EdgeSet::const_iterator
	Some typdefs and define for shortcuts ...
using	gum::NodeSetIterator = NodeSet::const_iterator
	Some typdefs and define for shortcuts ...
const NodeSet	gum::emptyNodeSet
	Some typdefs and define for shortcuts ...

Detailed Description

some utils for topology : NodeId, Edge, Arc and consorts ...

Author

Christophe GONZALES(_at_AMU) and Pierre-Henri WUILLEMIN(_at_LIP6)

This file provides two classes, namely Edge and Arc which represent respectively undirected and directed edges. The "directed/undirected" term may be misleading although in practice this will probably result in how these edges will be drawn. In fact, a more appropriate term would be "symmetric/asymmetric edges": an Arc is an edge in which the extremities have different status whereas in an Edge the role of the extremities is symmetric. For instance, in an arrow, one node is near the head and the other one is farther, hence these nodes have different status and swapping the nodes results in reversing the direction of the arrow. Thus, the nodes in an arrow can be thought of as asymmetric and the arrow's graphical representation contains a pointed extremity so as to account for this asymmetry. Conversely, in a Markov Random Field, an edge between two nodes, x and y, means that x and y are probabilistically dependent of one another. This being a symmetrical relation, there is no difference between edge (x,y) and edge (y,x). Thus, it can be represented by an Edge and, graphically, by an undirected edge.

Usage example:

// creation of an edge between nodes whose IDs are 3 and 4
Edge edge1 (3,4);
 
 
// copy the edge into another edge
Edge edge2 (edge1), edge3 = edge4;
 
// compare two edges
if (Edge(3,4) == Edge(4,3)) cerr << "ok, this is symmetric" << endl;
if (Edge(3,4) != Edge(5,4)) cerr << "different edges" << endl;
 
// get the extremities of the edge
cerr << edge1.first() << " = 3 and " << edge1.second() << " = 4\n";
cerr << "edge1 = (3," << edge1.other (3) << ")" << endl;
 
// display the edge in a console
cerr << edge1 << endl;
 
// creation of an arc (directed edge) from 3 to 4
Arc arc1 (3,4);
*
// compare two arcs
if (Arc(3,4) != Arc(4,3)) cerr << "ok, this is asymmetric" << endl;
 
// get the extremities of the edge
cerr << arc1.tail() << " = 3 and " << arc1.head() << " = 4\n";
cerr << "arc1 = (3 -> " << edge1.other (3) << ")" << endl;
 
// display an arc in a console
cerr << arc1 << endl;

Definition in file graphElements.h.