/*
  Impurity.java

  Definition of class ImpurityMeasure
  
  (P)2002  Dana Cristofor

*/

/*

GAClust - Clustering categorical databases using genetic algorithms
Copyright (C) 2002  Dana Cristofor


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., 59 Temple Place, Suite 330, Boston, MA 02111-1307
USA

GAClust was written by Dana Cristofor (dana@cs.umb.edu).

*/

/**
 * Impurity measures
 *
 * @version 	1.0
 * @author	Dana Cristofor
 */
public class ImpurityMeasure
{ 
  static public final int GINI    = 1;
  static public final int ENTROPY = 2;
  static public final int PEAK    = 3;
  static public final int CIRCLE  = 4;
  static public final int SINE    = 5;
  static public final int SQ      = 6;
  static public final int GE      = 7;

  static public double impurityMeasure(int type, double p)
  {
    if (type == GINI)
      return gini(p);
    else if (type == ENTROPY)
      return entropy(p);
    else if (type == PEAK)
      return peak(p);
    else if (type == CIRCLE)
      return circle(p);
    else if (type == SINE)
      return sine(p);
    else if (type == SQ)
      return sq(p);
    else if (type == GE)
      return ge(p);
    else
      return -1.0;
  }

  static private double gini(double p)
  {
    return (p - p * p);
  }

  static private double entropy(double p)
  {
    if (p == 0.0)
      return 0.0;
    else
      return (-p * Math.log(p) / Math.log(2));
  }

  static private double peak(double p)
  {
    if (p <= 0.5)
      return p;
    else
      return 1 - p;
  }

  static private double circle(double p)
  {
    return Math.sqrt(gini(p));
  }

  static private double sine(double p)
  {
    return Math.sin(p * Math.PI);
  }

  static private double sq(double p)
  {
    return Math.sqrt(p) - p;
  }

  static private double ge(double p)
  {
    return entropy(p - p*p);
  }

  static public double maxImpurityMeasure(int type, int n)
  {
    if (type == GINI)
      return max_gini(n);
    else if (type == ENTROPY)
      return max_entropy(n);
    else if (type == PEAK)
      return max_peak(n);
    else if (type == CIRCLE)
      return max_circle(n);
    else if (type == SINE)
      return max_sine(n);
    else if (type == SQ)
      return max_sq(n);
    else if (type == GE)
      return max_ge(n);
    else
      return -1.0;
  }

  static private double max_gini(int n)
  {
    return (1.0 - 1.0 / (double)n);
  }

  static private double max_entropy(int n)
  {
    return Math.log(n) / Math.log(2);
  }

  static private double max_peak(int n)
  {
    if (n == 1)
      return 0.0;
    else
      return 1.0;
  }

  static private double max_circle(int n)
  {
    return Math.sqrt(n - 1);
  }

  static private double max_sine(int n)
  {
    return (double)n * Math.sin(Math.PI / ((double)n));
  }
  
  static private double max_sq(int n)
  {
    return Math.sqrt(n) - 1.0;
  }

  static private double max_ge(int n)
  {
    return (((double)(n-1))/n)*Math.log(((double)(n-1))/(n*n)) / Math.log(2);
  }
}