org.moeaframework.core
Class AdaptiveGridArchive

java.lang.Object
  org.moeaframework.core.Population
      org.moeaframework.core.NondominatedPopulation
          org.moeaframework.core.AdaptiveGridArchive

All Implemented Interfaces:

Iterable<Solution>

public class AdaptiveGridArchive
extends NondominatedPopulation

Adaptive grid archive. Divides objective space into a number of grid cells, maintaining a count of the number of solutions within each grid cell. When the size of the archive exceeds a specified capacity, a solution from the most crowded grid cell is selected and removed from the archive.

References:

1. Knowles, J.D. and Corne, D.W., "Approximating the Nondominated Front using the Pareto Archived Evolution Strategy," Evolutionary Computation, vol. 8, no. 2, pp. 149-172, 2000.
2. Knowles, J.D. and Corne, D.W., "Properties of an Adaptive Archiving for Storing Nondominated Vectors," IEEE Transactions on Evolutionary Computation, vol. 7, no. 2, pp. 100-116, 2003.

Field Summary

protected int	capacity The maximum capacity of this archive.
protected int[]	density The number of solutions in each grid cell.
protected double[]	maximum The maximum objective value for each dimension.
protected double[]	minimum The minimum objective value for each dimension.
protected int	numberOfDivisions The number of divisions this archive uses to split each objective.
protected Problem	problem The problem for which this archive is used.

Constructor Summary

AdaptiveGridArchive(int capacity, Problem problem, int numberOfDivisions)
Constructs an adaptive grid archive with the specified capacity with the specified number of divisions along each objective.

Method Summary

protected void	adaptGrid() Computes new lower and upper bounds and recalculates the densities of each grid cell.
boolean	add(Solution solution) If newSolution is dominates any solution or is non-dominated with all solutions in this population, the dominated solutions are removed and newSolution is added to this population.
void	clear() Removes all solutions from this population.
protected int	findDensestIndex() Returns the index of the solution residing in the densest grid cell.
int	findIndex(Solution solution) Returns the index of the specified solution in this adaptive grid archive, or -1 if the solution is not within the current lower and upper bounds.
int	getCapacity() Returns the maximum number of solutions stored in this archive.
int	getDensity(int index) Returns the density of the solution at the given index.
int	getNumberOfDivisions() Returns the number of divisions this archive uses to split each objective.
Problem	getProblem() Returns the problem for which this archive is used.
void	remove(int index) Removes the solution at the specified index from this population.
boolean	remove(Solution solution) Removes the specified solution from this population, if present.

Methods inherited from class org.moeaframework.core.NondominatedPopulation

distance, forceAddWithoutCheck, getComparator

Methods inherited from class org.moeaframework.core.Population

addAll, addAll, contains, containsAll, containsAll, get, indexOf, isEmpty, iterator, removeAll, removeAll, size, sort, truncate

Methods inherited from class java.lang.Object

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

Field Detail

capacity

protected final int capacity

The maximum capacity of this archive.

problem

protected final Problem problem

The problem for which this archive is used.

numberOfDivisions

protected final int numberOfDivisions

The number of divisions this archive uses to split each objective.

minimum

protected double[] minimum

The minimum objective value for each dimension.

maximum

protected double[] maximum

The maximum objective value for each dimension.

density

protected int[] density

The number of solutions in each grid cell.

Constructor Detail

AdaptiveGridArchive

public AdaptiveGridArchive(int capacity,
                           Problem problem,
                           int numberOfDivisions)

Constructs an adaptive grid archive with the specified capacity with the specified number of divisions along each objective.

Parameters:

capacity - the capacity of this archive

problem - the problem for which this archive is used

numberOfDivisions - the number of divisions this archive uses to split each objective

Method Detail

getCapacity

public int getCapacity()

Returns the maximum number of solutions stored in this archive.

Returns:

the maximum number of solutions stored in this archive

getNumberOfDivisions

public int getNumberOfDivisions()

Returns the number of divisions this archive uses to split each objective.

Returns:

the number of divisions this archive uses to split each objective

getProblem

public Problem getProblem()

Returns the problem for which this archive is used.

Returns:

the problem for which this archive is used

add

public boolean add(Solution solution)

Description copied from class: NondominatedPopulation

If newSolution is dominates any solution or is non-dominated with all solutions in this population, the dominated solutions are removed and newSolution is added to this population. Otherwise, newSolution is dominated and is not added to this population.

Overrides:

add in class NondominatedPopulation

Parameters:

solution - the solution to be added

Returns:

true if the population was modified as a result of this method; false otherwise.

remove

public void remove(int index)

Description copied from class: Population

Removes the solution at the specified index from this population.

Overrides:

remove in class Population

Parameters:

index - the index of the solution to be removed

remove

public boolean remove(Solution solution)

Description copied from class: Population

Removes the specified solution from this population, if present.

Overrides:

remove in class Population

Parameters:

solution - the solution to be removed

Returns:

true if this population was modified as a result of this method; false otherwise

clear

public void clear()

Description copied from class: Population

Removes all solutions from this population.

Overrides:

clear in class Population

findDensestIndex

protected int findDensestIndex()

Returns the index of the solution residing in the densest grid cell. If there are more than one such solutions, the first value is returned.

Returns:

the index of the solution residing in the densest grid cell

adaptGrid

protected void adaptGrid()

Computes new lower and upper bounds and recalculates the densities of each grid cell.

findIndex

public int findIndex(Solution solution)

Returns the index of the specified solution in this adaptive grid archive, or -1 if the solution is not within the current lower and upper bounds.

Parameters:

solution - the specified solution

Returns:

the index of the specified solution in this adaptive grid archive, or -1 if the solution is not within the current lower and upper bounds

getDensity

public int getDensity(int index)

Returns the density of the solution at the given index.

Parameters:

index - the solution index

Returns:

the density of the solution at the given index