org.graphstream.algorithm

Class Centroid

java.lang.Object

org.graphstream.algorithm.Centroid

All Implemented Interfaces:

Algorithm

public class Centroid
extends Object
implements Algorithm

Compute the centroid of a connected graph.

In a graph G, if d(u,v) is the shortest length between two nodes u and v (ie the number of edges of the shortest path) let m(u) be the sum of d(u,v) for all nodes v of G. Centroid of a graph G is a subgraph induced by vertices u with minimum m(u).

Requirements

This algorithm needs that APSP algorithm has been computed before its own computation.

Example

 import java.io.StringReader;
 import java.io.IOException;
 
 import org.graphstream.algorithm.APSP;
 import org.graphstream.algorithm.Centroid;
 import org.graphstream.graph.Graph;
 import org.graphstream.graph.Node;
 import org.graphstream.graph.implementations.DefaultGraph;
 import org.graphstream.stream.file.FileSourceDGS;
 
 //                     +--- E
 // A --- B --- C -- D -|--- F
 //                     +--- G
 
 public class CentroidTest {
        static String my_graph = "DGS004\n" + "my 0 0\n" + "an A \n" + "an B \n"
                        + "an C \n" + "an D \n" + "an E \n" + "an F \n" + "an G \n"
                        + "ae AB A B \n" + "ae BC B C \n" + "ae CD C D \n" + "ae DE D E \n"
                        + "ae DF D F \n" + "ae DG D G \n";
 
        public static void main(String[] args) throws IOException {
                Graph graph = new DefaultGraph("Centroid Test");
                StringReader reader = new StringReader(my_graph);
 
                FileSourceDGS source = new FileSourceDGS();
                source.addSink(graph);
                source.readAll(reader);
 
                APSP apsp = new APSP();
                apsp.init(graph);
                apsp.compute();
 
                Centroid centroid = new Centroid();
                centroid.init(graph);
                centroid.compute();
 
                for (Node n : graph.getEachNode()) {
                        Boolean in = n.getAttribute("centroid");
 
                        System.out.printf("%s is%s in the centroid.\n", n.getId(), in ? ""
                                        : " not");
                }
 
                // Output will be :
                //
                // A is not in the centroid
                // B is not in the centroid
                // C is not in the centroid
                // D is in the centroid
                // E is not in the centroid
                // F is not in the centroid
                // G is not in the centroid
        }
 }
 

See Also:

APSP.APSPInfo

Computational Complexity :

O(n2)

Scientific Reference :

F. Harary, Graph Theory. Westview Press, Oct. 1969. [Online]. Available: http://www.amazon.com/exec/obidos/ redirect?tag=citeulike07-20\&path=ASIN/ 0201410338

Constructor Summary

Constructors

Constructor and Description
Centroid() Build a new centroid algorithm with default parameters.
Centroid(String centroidAttribute) Build a new centroid algorithm, specifying the attribute name of the computation result
Centroid(String centroidAttribute, Object isInCentroid, Object isNotInCentroid) Build a new centroid as in Centroid(String) but specifying values of centroid membership.
Centroid(String centroidAttribute, Object isInCentroid, Object isNotInCentroid, String apspInfoAttribute) Build a new centroid algorithm as in Centroid(String, Object, Object) but specifying the name of the attribute where the APSP informations are stored.

Method Summary

Methods

Modifier and Type	Method and Description
void	compute() Run the algorithm.
String	getAPSPInfoAttribute() Get the APSP info attribute name.
String	getCentroidAttribute() Get the name of the attribute where computation result is stored.
Object	getIsInCentroidValue() Get the value of the centroid attribute when element is in the centroid.
Object	getIsNotInCentroidValue() Get the value of the centroid attribute when element is not in the centroid.
void	init(org.graphstream.graph.Graph graph) Initialization of the algorithm.
void	setAPSPInfoAttribute(String attribute) Set the APSP info attribute name.
void	setCentroidAttribute(String centroidAttribute) Set the name of the attribute where computation result is stored.
void	setIsInCentroidValue(Object value) Set the value of the centroid attribute when element is in the centroid.
void	setIsNotInCentroidValue(Object value) Set the value of the centroid attribute when element is not in the centroid.

Methods inherited from class java.lang.Object

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

Constructor Detail

Centroid

public Centroid()

Build a new centroid algorithm with default parameters.

Centroid

public Centroid(String centroidAttribute)

Build a new centroid algorithm, specifying the attribute name of the computation result

Parameters:

centroidAttribute - attribute name of the computation result.

Centroid

public Centroid(String centroidAttribute,
        Object isInCentroid,
        Object isNotInCentroid)

Build a new centroid as in Centroid(String) but specifying values of centroid membership.

Parameters:

centroidAttribute - attribute name of the computation result.

isInCentroid - the value of elements centroid attribute when this element is in the centroid.

isNotInCentroid - the value of elements centroid attribute when this element is not in the centroid.

Centroid

public Centroid(String centroidAttribute,
        Object isInCentroid,
        Object isNotInCentroid,
        String apspInfoAttribute)

Build a new centroid algorithm as in Centroid(String, Object, Object) but specifying the name of the attribute where the APSP informations are stored.

Parameters:

centroidAttribute - attribute name of the computation result.

isInCentroid - the value of elements centroid attribute when this element is in the centroid.

isNotInCentroid - the value of elements centroid attribute when this element is not in the centroid.

apspInfoAttribute - the name of the attribute where the APSP informations are stored

Method Detail

init

public void init(org.graphstream.graph.Graph graph)

Description copied from interface: Algorithm

Initialization of the algorithm. This method has to be called before the Algorithm.compute() method to initialize or reset the algorithm according to the new given graph.

Specified by:

init in interface Algorithm

Parameters:

graph - The graph this algorithm is using.

compute

public void compute()

Description copied from interface: Algorithm

Run the algorithm. The Algorithm.init(Graph) method has to be called before computing.

Specified by:

compute in interface Algorithm

See Also:

Algorithm.init(Graph)

getAPSPInfoAttribute

public String getAPSPInfoAttribute()

Get the APSP info attribute name.

Returns:

the name of the attribute where the APSP informations are stored.

setAPSPInfoAttribute

public void setAPSPInfoAttribute(String attribute)

Set the APSP info attribute name.

Parameters:

attribute - the name of the attribute where the APSP informations are stored.

getIsInCentroidValue

public Object getIsInCentroidValue()

Get the value of the centroid attribute when element is in the centroid. Default value is Boolean.TRUE.

Returns:

the value of elements centroid attribute when this element is in the centroid.

setIsInCentroidValue

public void setIsInCentroidValue(Object value)

Set the value of the centroid attribute when element is in the centroid. On computation, this value is used to set the centroid attribute.

Parameters:

value - the value of elements centroid attribute when this element is in the centroid.

getIsNotInCentroidValue

public Object getIsNotInCentroidValue()

Get the value of the centroid attribute when element is not in the centroid. Default value is Boolean.FALSE.

Returns:

the value of elements centroid attribute when this element is not in the centroid.

setIsNotInCentroidValue

public void setIsNotInCentroidValue(Object value)

Set the value of the centroid attribute when element is not in the centroid. On computation, this value is used to set the centroid attribute.

Parameters:

value - the value of elements centroid attribute when this element is not in the centroid.

getCentroidAttribute

public String getCentroidAttribute()

Get the name of the attribute where computation result is stored. Value of this attribute can be getIsInCentroidValue() if the element is in the centroid, getIsNotInCentroidValue() else.

Returns:

the centroid attribute name.

setCentroidAttribute

public void setCentroidAttribute(String centroidAttribute)

Set the name of the attribute where computation result is stored.

Parameters:

centroidAttribute - the name of the element attribute where computation result is stored.