www.pudn.com > weka.rar > EntropyBasedSplitCrit.java, change:2001-03-14,size:2447b

```/*
*    This program is free software; you can redistribute it and/or modify
*    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., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

/*
*    EntropyBasedSplitCrit.java
*    Copyright (C) 1999 Eibe Frank
*
*/

package weka.classifiers.j48;

/**
* "Abstract" class for computing splitting criteria
* based on the entropy of a class distribution.
*
* @author Eibe Frank (eibe@cs.waikato.ac.nz)
* @version \$Revision: 1.4 \$
*/
public abstract class EntropyBasedSplitCrit extends SplitCriterion{

/** The log of 2. */
protected static double log2 = Math.log(2);

/**
* Help method for computing entropy.
*/
protected final double logFunc(double num) {

// Constant hard coded for efficiency reasons
if (num < 1e-6)
return 0;
else
return num*Math.log(num)/log2;
}

/**
* Computes entropy of distribution before splitting.
*/
public final double oldEnt(Distribution bags) {

double returnValue = 0;
int j;

for (j=0;j<bags.numClasses();j++)
returnValue = returnValue+logFunc(bags.perClass(j));
return logFunc(bags.total())-returnValue;
}

/**
* Computes entropy of distribution after splitting.
*/
public final double newEnt(Distribution bags) {

double returnValue = 0;
int i,j;

for (i=0;i<bags.numBags();i++){
for (j=0;j<bags.numClasses();j++)
returnValue = returnValue+logFunc(bags.perClassPerBag(i,j));
returnValue = returnValue-logFunc(bags.perBag(i));
}
return -returnValue;
}

/**
* Computes entropy after splitting without considering the
* class values.
*/
public final double splitEnt(Distribution bags) {

double returnValue = 0;
int i;

for (i=0;i<bags.numBags();i++)
returnValue = returnValue+logFunc(bags.perBag(i));
return logFunc(bags.total())-returnValue;
}
}

```