pareto.java

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/**    
  * Copyright (C) 2006, Laboratorio di Valutazione delle Prestazioni - Politecnico di Milano

  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation; either version 2 of the License, or
  * (at your option) any later version.

  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.

  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  */
  
package jmt.gui.common.distributions;

import jmt.gui.common.resources.ImageLoader;

import javax.swing.*;

/**
 * <p>Title: Pareto Distribution</p>
 * <p>Description: Pareto distribution data structure</p>
 * 
 * @author Bertoli Marco
 *         Date: 28-giu-2005
 *         Time: 10.47.42
 */
public class Pareto extends Distribution{
    /**
     * Construct a new Pareto Distribution
     */
    public Pareto() {
        super("Pareto",
                "jmt.engine.random.Pareto",
                "jmt.engine.random.ParetoPar",
                "Pareto distribution");
        hasMean = true;
        hasC = true;
    }

    /**
     * Used to set parameters of this distribution.
     * @return distribution parameters
     */
    protected Parameter[] setParameters() {
        // Creates parameter array
        Parameter[] parameters = new Parameter[2];
        // Sets parameter alpha
        parameters[0] = new Parameter("alpha",
                "\u03B1",
                Double.class,
                new Double(3));
        // Checks value of alpha must greater or equal then 2
        parameters[0].setValueChecker(new ValueChecker() {
            public boolean checkValue(Object value) {
                Double d = (Double) value;
                if (d.doubleValue() >= 2)
                    return true;
                else
                    return false;
            }
        });

        // Sets parameter k
        parameters[1] = new Parameter("k",
                "k",
                Double.class,
                new Double(1));
        // Checks value of k must be greater then 0
        parameters[1].setValueChecker(new ValueChecker() {
            public boolean checkValue(Object value) {
                Double d = (Double) value;
                if (d.doubleValue() > 0)
                    return true;
                else
                    return false;
            }
        });

        return parameters;
    }

    /**
     * Sets explicative image of this distribution used, together with description, to help the
     * user to understand meaning of parameters.
     * @return explicative image
     */
    protected ImageIcon setImage() {
        return ImageLoader.loadImage("Pareto");
    }

    /**
     * Returns this distribution's short description
     * @return distribution's short description
     */
    public String toString() {
        return "par(" +
                FormatNumber(((Double)parameters[0].getValue()).doubleValue()) +
                "; "+
                FormatNumber(((Double)parameters[1].getValue()).doubleValue()) +
                ")";
    }

    /**
     * Sets the mean for this distribution
     * @param value mean value
     */
    public void setMean(double value) {
        setCM(value, c);
    }

    /**
     * Sets the variation coefficient C for this distribution
     * @param value variation coefficient C value
     */
    public void setC (double value) {
        setCM(mean, value);
    }

    /**
     * Sets Mean and C values
     * @param mean mean value
     * @param c c value
     */
    protected void setCM(double mean, double c) {
        // k = mean - mean /  (1+sqrt(1+1/c^2)) && alpha = 1 + sqrt(1 + 1 / c^2)
        // Backups old parameters to restore them upon a false result
        Object oldk = getParameter("k").getValue();
        Object olda = getParameter("alpha").getValue();
        if (getParameter("k").setValue(new Double(mean - mean / (1 + Math.sqrt(1+1/(c*c))))) &&
                getParameter("alpha").setValue(new Double(1 + Math.sqrt(1 + 1 / (c*c))))) {
            this.mean = mean;
            this.c = c;
        }
        else {
            getParameter("k").setValue(oldk);
            getParameter("alpha").setValue(olda);
        }
    }

    /**
     * This method is called whenever a parameter changes and <code>hasC</code> or
     * <code>hasMean</code> are true
     */
    public void updateCM() {
        double a, k;
        a = ((Double)getParameter("alpha").getValue()).doubleValue();
        k = ((Double)getParameter("k").getValue()).doubleValue();
        mean = a * k / (a - 1);
        c = 1 / Math.sqrt(a * a - 2 * a);
    }                                   
}