spectrumfilter.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;

/** Creates a series of peaks (a spectrum) from the series of complex values calculated for example by a fourier transform. 
 *  Since the FT input values must not be equivalent the magnitudes of the spectrum do not correspond to the real amplitudes. 
 *  Like the human ear this filter tries to calculate more accurate values (see ERB or Bark filters). 
 *
 *  @version $Id: SpectrumFilter.java,v 1.2 2004/08/27 11:57:46 ingomierswa Exp $
 */
public class SpectrumFilter {

    public static final int NONE = 0;
    public static final int ERB  = 1;
    public static final int LOG  = 2;
    public static final int LOG2 = 3;

    private int weightType;

    public SpectrumFilter(int weightType) {
	this.weightType = weightType;
    }

    public Peak[] filter(Complex[] spectrum, int totalSize) {
	Peak[] result = new Peak[spectrum.length];
	for (int i = 0; i < result.length; i++) {
	    result[i] = new Peak(FastFourierTransform.convertFrequency(i, spectrum.length, totalSize), 
				 filterValue(spectrum[i].getMagnitude(spectrum.length * 2), i));
	}
	return result;
    }
    
    private double filterValue(double value, int index) {
	switch (weightType) {
	case ERB: return value * (21.4d * Math.log(0.00437d * index + 1.0d) / Math.log(10.0d));
	case LOG: return value * (10.0d * Math.log(index + 1) / Math.log(20.0d));
	case LOG2: return value * (0.7d * Math.log(5 * index + 1)); 
	default: return value;
	}
    }
}