/*
* 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.tools.math;
/**
* Window functions apply a weight to each value of a value series depending on
* the length of the series. Window Functions like Hanning windows are usually
* applied before a Fourier transformation.
*
* @author Ingo Mierswa
* @version $Id: WindowFunction.java,v 1.3 2008/05/09 19:23:03 ingomierswa Exp $
*/
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) / length);
default:
return 1.0;
}
}
}