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## Class GnmRandomGraphGenerator<V,E>

• Type Parameters:
V - the graph vertex type
E - the graph edge type
All Implemented Interfaces:
GraphGenerator<V,E,V>

public class GnmRandomGraphGenerator<V,E>
extends Object
implements GraphGenerator<V,E,V>
Create a random graph based on the $G(n, M)$ Erdős–Rényi model. See the Wikipedia article for details and references about Random Graphs and the Erdős–Rényi model .

In the $G(n, M)$ model, a graph is chosen uniformly at random from the collection of all graphs which have $n$ nodes and $M$ edges. For example, in the $G(3, 2)$ model, each of the three possible graphs on three vertices and two edges are included with probability $\frac{1}{3}$.

The implementation creates the vertices and then randomly chooses an edge and tries to add it. If the add fails for any reason (an edge already exists and multiple (parallel) edges are not allowed) it will just choose another and try again. The performance therefore varies significantly based on the probability of successfully constructing an acceptable edge.

The implementation tries to guess the number of allowed edges based on the following. If self-loops or multiple edges are allowed and requested, the maximum number of edges is Integer.MAX_VALUE. Otherwise the maximum for undirected graphs with n vertices is $\frac{n(n-1)}{2}$ while for directed $n(n-1)$.

For the $G(n, p)$ model please see GnpRandomGraphGenerator.

Author:
Assaf Lehr, Dimitrios Michail
See Also:
GnpRandomGraphGenerator
• ### Constructor Summary

Constructors
Constructor and Description
GnmRandomGraphGenerator(int n, int m)
Create a new $G(n, M)$ random graph generator.
GnmRandomGraphGenerator(int n, int m, long seed)
Create a new $G(n, M)$ random graph generator.
GnmRandomGraphGenerator(int n, int m, long seed, boolean loops, boolean multipleEdges)
Create a new $G(n, M)$ random graph generator
GnmRandomGraphGenerator(int n, int m, Random rng, boolean loops, boolean multipleEdges)
Create a new $G(n, M)$ random graph generator
• ### Method Summary

All Methods
Modifier and Type Method and Description
void generateGraph(Graph<V,E> target, Map<String,V> resultMap)
Generates a random graph based on the $G(n, M)$ model
• ### Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
• ### Methods inherited from interface org.jgrapht.generate.GraphGenerator

generateGraph
• ### Constructor Detail

• #### GnmRandomGraphGenerator

public GnmRandomGraphGenerator(int n,
int m)
Create a new $G(n, M)$ random graph generator. The generator does not create self-loops or multiple (parallel) edges between the same two vertices.
Parameters:
n - the number of nodes
m - the number of edges
• #### GnmRandomGraphGenerator

public GnmRandomGraphGenerator(int n,
int m,
long seed)
Create a new $G(n, M)$ random graph generator. The generator does not create self-loops or multiple (parallel) edges between the same two vertices.
Parameters:
n - the number of nodes
m - the number of edges
seed - seed for the random number generator
• #### GnmRandomGraphGenerator

public GnmRandomGraphGenerator(int n,
int m,
long seed,
boolean loops,
boolean multipleEdges)
Create a new $G(n, M)$ random graph generator
Parameters:
n - the number of nodes
m - the number of edges
seed - seed for the random number generator
loops - whether the generated graph may contain loops
multipleEdges - whether the generated graph many contain multiple (parallel) edges between the same two vertices
• #### GnmRandomGraphGenerator

public GnmRandomGraphGenerator(int n,
int m,
Random rng,
boolean loops,
boolean multipleEdges)
Create a new $G(n, M)$ random graph generator
Parameters:
n - the number of nodes
m - the number of edges
rng - the random number generator
loops - whether the generated graph may contain loops
multipleEdges - whether the generated graph many contain multiple (parallel) edges between the same two vertices
• ### Method Detail

• #### generateGraph

public void generateGraph(Graph<V,E> target,
Map<String,V> resultMap)
Generates a random graph based on the $G(n, M)$ model
Specified by:
generateGraph in interface GraphGenerator<V,E,V>
Parameters:
target - the target graph
resultMap - not used by this generator, can be null
Throws:
IllegalArgumentException - if the number of edges, passed in the constructor, cannot be created on a graph of the concrete type with the specified number of vertices
IllegalArgumentException - if the graph does not support a requested feature such as self-loops or multiple (parallel) edges
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