windowfunction.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;

public class WindowFunction {

    /** The currently implemented window functions. */
    public static final String[] FUNCTIONS = {
	"None", "Hanning", "Hamming", "Blackman", "Blackman-Harris", "Bartlett", "Rectangle"
    };
    
    /** The constant for the function Hanning. */
    public static final int NONE            = 0;
    /** The constant for the function Hanning. */
    public static final int HANNING         = 1;
    /** The constant for the function Hamming. */
    public static final int HAMMING         = 2;
    /** The constant for the function Blackman. */
    public static final int BLACKMAN        = 3;
    /** The constant for the function Blackman-Harris. */
    public static final int BLACKMAN_HARRIS = 4;
    /** The constant for the function Bartlett. */
    public static final int BARTLETT        = 5;
    /** The constant for the function Rectangle. */
    public static final int RECTANGLE       = 6;

    private int type;
    private int length;

    public WindowFunction(int type, int maxIndex) {
	this.type = type;
	this.length = maxIndex;
    }

    /** Returns the weighting factor for the current value n in a window of the given length. The calculation
     *  of this factor is done in dependance of the function type.  */
    public double getFactor(int n) {
	switch (type) {
	    case HANNING:
		return 0.5 - 0.5 * Math.cos(2 * Math.PI * n / length);
	    case HAMMING:
		return 0.54 - 0.46 * Math.cos(2 * Math.PI * n / length);
	    case BLACKMAN:
		return 0.42 - 0.5 * Math.cos(2 * Math.PI * n / length) + 0.08 * Math.cos(4 * Math.PI * n / length);
	    case BLACKMAN_HARRIS:
		return 
		    0.35875 - 
		    0.48829 * Math.cos(2 * Math.PI * n / length) + 
		    0.14128 * Math.cos(4 * Math.PI * n / length) - 
		    0.01168 * Math.cos(6 * Math.PI * n / length);
	    case BARTLETT:
		return 1.0 - Math.abs(2 * (double)(n - length / 2) / (double)length);
	    default:
		return 1.0;
	}
    }
}