/*
* RapidMiner
*
* Copyright (C) 2001-2008 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.rvm.kernel;
/**
* Returns the value of the Sigmoid kernel of both examples.
*
* @author Ingo Mierswa
* @version $Id: KernelSigmoid.java,v 1.3 2008/05/09 19:23:26 ingomierswa Exp $
*/
public class KernelSigmoid extends Kernel {
private static final long serialVersionUID = 5056175330389455467L;
/** The parameter a of the sigmoid kernel. */
private double a = 1.0d;
/** The parameter b of the sigmoid kernel. */
private double b = 0.0d;
/** Constructor(s) */
public KernelSigmoid(double a, double b) {
super();
this.a = a;
this.b = b;
}
public KernelSigmoid() {
super();
}
public double eval(double[] x, double[] y) {
// K = tanh(a(x*y)+b)
double prod = 0;
for (int i = 0; i < x.length; i++) {
prod += x[i] * y[i];
}
prod = a * prod + b;
double e1 = Math.exp(prod);
double e2 = Math.exp(-prod);
return ((e1 - e2) / (e1 + e2));
}
public String toString() {
return "sigmoid kernel [a = " + a + ", b = " + b + "]";
}
}