mathfunctions.java

一个很好的LIBSVM的JAVA源码。对于要研究和改进SVM算法的学者。可以参考。来自数据挖掘工具YALE工具包。

/*
 *  YALE - Yet Another Learning Environment
 *  Copyright (C) 2001-2004
 *      Simon Fischer, Ralf Klinkenberg, Ingo Mierswa, 
 *          Katharina Morik, Oliver Ritthoff
 *      Artificial Intelligence Unit
 *      Computer Science Department
 *      University of Dortmund
 *      44221 Dortmund,  Germany
 *  email: [e-mail]
 *  web:   http://yale.cs.uni-dortmund.de/
 *
 *  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.
 */
package edu.udo.cs.yale.tools.math;

/** This class provides mathematical functions not already provided by <tt>java.lang.Math</tt>:
 *  <ul>
 *    <li><tt>tanh()</tt> : tangens hyperbolicus, <i>y = tanh(x) = (e^x - e^-x) / (e^x + e^-x)</i></li>
 *  </ul>
 *  
 *  @author Ralf Klinkenberg
 *  @version 2002/05/25
 */

public class MathFunctions {
    /** returns tangens hyperbolicus of <tt>x</tt>, i.e. 
     *  <i>y = tanh(x) = (e^x - e^-x) / (e^x + e^-x)</i>.
     */
    public static double  tanh(double x) {
	return ((java.lang.Math.exp(x) - java.lang.Math.exp(-x)) / (java.lang.Math.exp(x) + java.lang.Math.exp(-x)));
    }
}