/*
* 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.functions;
/**
* Returns the value of a Sigmoid kernel of both examples.
*
* @author Ingo Mierswa
* @version $Id: SigmoidKernel.java,v 1.4 2008/09/12 10:29:42 tobiasmalbrecht Exp $
*/
public class SigmoidKernel extends Kernel {
private static final long serialVersionUID = -4503893127271607088L;
/** The parameter a of the sigmoid kernel. */
private double a = 1.0d;
/** The parameter b of the sigmoid kernel. */
private double b = 0.0d;
public int getType() {
return KERNEL_SIGMOID;
}
/** Sets the parameters of this Sigmoid kernel to the given values a and b. */
public void setSigmoidParameters(double a, double b) {
this.a = a;
this.b = b;
}
/** Subclasses must implement this method. */
public double calculateDistance(double[] x1, double[] x2) {
// K = tanh(a(x*y)+b)
double prod = a * innerProduct(x1, x2) + b;
double e1 = Math.exp(prod);
double e2 = Math.exp(-prod);
return ((e1 - e2) / (e1 + e2));
}
}