org.jgap.gp.function.statistics.Skewness.java Source code

Introduction

Here is the source code for org.jgap.gp.function.statistics.Skewness.java

Source

/*
 * This file is part of JGAP.
 *
 * JGAP offers a dual license model containing the LGPL as well as the MPL.
 *
 * For licensing information please see the file license.txt included with JGAP
 * or have a look at the top of class org.jgap.Chromosome which representatively
 * includes the JGAP license policy applicable for any file delivered with JGAP.
 */
package org.jgap.gp.function.statistics;

import org.apache.commons.math.stat.descriptive.*;
import org.jgap.*;
import org.jgap.gp.*;
import org.jgap.gp.impl.*;
import org.jgap.util.*;

/**
 * Computes the skewness of the available values.
 * <p>
 * We use the following (unbiased) formula to define skewness:</p>
 * <p>
 * skewness = [n / (n -1) (n - 2)] sum[(x_i - mean)^3] / std^3 </p>
 * <p>
 * where n is the number of values, and std is the Standard Deviation </p>
 *
 * @author Luis Garcia
 * @since 3.5
 */
public class Skewness extends CommandDynamicArity implements ICloneable {
    public Skewness(final GPConfiguration a_conf, Class a_returnType, int a_arityInitial, int a_arityMin,
            int a_arityMax) throws InvalidConfigurationException {
        super(a_conf, a_arityInitial + 1, a_arityMin + 1, a_arityMax + 1, a_returnType);
    }

    @Override
    public double execute_double(ProgramChromosome c, int n, Object[] args) {
        int size = size();
        DescriptiveStatistics stats = new DescriptiveStatistics();
        for (int i = 0; i < size; i++) {
            stats.addValue(c.execute_double(n, i, args));
        }
        return stats.getSkewness();
    }

    @Override
    public float execute_float(ProgramChromosome c, int n, Object[] args) {
        int size = size();
        DescriptiveStatistics stats = new DescriptiveStatistics();
        for (int i = 0; i < size; i++) {
            stats.addValue(c.execute_float(n, i, args));
        }
        return (float) stats.getSkewness();
    }

    @Override
    public String toString() {
        String s = "Skewness(";
        int size = size();
        for (int i = 0; i < size; i++) {
            if (i > 0) {
                s += ";";
            }
            s += "&" + (i + 1);
        }
        return s + ")";
    }

    @Override
    public Object clone() {
        try {
            Skewness result = new Skewness(getGPConfiguration(), getReturnType(), getArity(null), getArityMin(),
                    getArityMax());
            return result;
        } catch (Exception ex) {
            throw new CloneException(ex);
        }
    }

    @Override
    public String getName() {
        return "Skewness";
    }
}