/*
* RapidMiner
*
* Copyright (C) 2001-2011 by Rapid-I and the contributors
*
* Complete list of developers available at our web site:
*
* http://rapid-i.com
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as published by
* the Free Software Foundation, either version 3 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 Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see http://www.gnu.org/licenses/.
*/
package com.rapidminer.operator.learner.functions.kernel.jmysvm.kernel;
import com.rapidminer.tools.Tools;
/**
* Neural Kernel
*
* @author Stefan Rueping, Ingo Mierswa
*/
public class KernelNeural extends Kernel {
private static final long serialVersionUID = 3862702323530107467L;
double a = 1.0;
double b = 0.0;
/**
* Class constructor
*/
public KernelNeural() {};
/**
* Output as String
*/
@Override
public String toString() {
return ("neural(" + a + "," + b + ")");
};
public void setParameters(double a, double b) {
this.a = a;
this.b = b;
}
/**
* Calculates kernel value of vectors x and y
*/
@Override
public double calculate_K(int[] x_index, double[] x_att, int[] y_index, double[] y_att) {
// K = tanh(a(x*y)+b)
double prod = a * innerproduct(x_index, x_att, y_index, y_att) + b;
double e1 = Math.exp(prod);
double e2 = Math.exp(-prod);
return ((e1 - e2) / (e1 + e2));
}
@Override
public String getDistanceFormula(double[] x, String[] attributeConstructions) {
StringBuffer result = new StringBuffer();
boolean first = true;
for (int i = 0; i < x.length; i++) {
double value = x[i];
if (!Tools.isZero(value)) {
if (value < 0.0d) {
if (first)
result.append("-" + Math.abs(value) + " * " + attributeConstructions[i]);
else
result.append(" - " + Math.abs(value) + " * " + attributeConstructions[i]);
} else {
if (first)
result.append(value + " * " + attributeConstructions[i]);
else
result.append(" + " + value + " * " + attributeConstructions[i]);
}
first = false;
}
}
String e1 = "exp(" + result.toString() + ")";
String e2 = "exp(-1 * (" + result.toString() + "))";
return "((" + e1 + " - " + e2 + ") / (" + e1 + " + " + e2 + "))";
}
};