org.jgrapht.alg.scoring

Class Coreness<V,E>

java.lang.Object

org.jgrapht.alg.scoring.Coreness<V,E>

Type Parameters:

V - the graph vertex type

E - the graph edge type

All Implemented Interfaces:

VertexScoringAlgorithm<V,Integer>

public final class Coreness<V,E>
extends Object
implements VertexScoringAlgorithm<V,Integer>

Computes the coreness of each vertex in an undirected graph.

A $k$-core of a graph $G$ is a maximal connected subgraph of $G$ in which all vertices have degree at least $k$. Equivalently, it is one of the connected components of the subgraph of $G$ formed by repeatedly deleting all vertices of degree less than $k$. A vertex $u$ has coreness $c$ if it belongs to a $c$-core but not to any $(c+1)$-core.

If a non-empty k-core exists, then, clearly, $G$ has degeneracy at least $k$, and the degeneracy of $G$ is the largest $k$ for which $G$ has a $k$-core.

As described in the following paper

• D. W. Matula and L. L. Beck. Smallest-last ordering and clustering and graph coloring algorithms. Journal of the ACM, 30(3):417--427, 1983.

it is possible to find a vertex ordering of a finite graph $G$ that optimizes the coloring number of the ordering, in linear time, by using a bucket queue to repeatedly find and remove the vertex of smallest degree.

Author:

Dimitrios Michail

Constructor Summary

Constructors

Constructor and Description
Coreness(Graph<V,E> g) Constructor

Method Summary

Modifier and Type	Method and Description
int	getDegeneracy() Compute the degeneracy of a graph.
Map<V,Integer>	getScores() Get a map with the scores of all vertices
Integer	getVertexScore(V v) Get a vertex score

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Coreness

public Coreness(Graph<V,E> g)

Constructor

Parameters:

g - the input graph

Method Detail

getScores

public Map<V,Integer> getScores()

Get a map with the scores of all vertices

Specified by:

getScores in interface VertexScoringAlgorithm<V,Integer>

Returns:

a map with all scores

getVertexScore

public Integer getVertexScore(V v)

Get a vertex score

Specified by:

getVertexScore in interface VertexScoringAlgorithm<V,Integer>

Parameters:

v - the vertex

Returns:

the score

getDegeneracy

public int getDegeneracy()

Compute the degeneracy of a graph.

The degeneracy of a graph is the smallest value of $k$ for which it is $k$-degenerate. In graph theory, a $k$-degenerate graph is an undirected graph in which every subgraph has a vertex of degree at most $k$: that is, some vertex in the subgraph touches $k$ or fewer of the subgraph's edges.

Returns:

the degeneracy of a graph