/**
* Copyright (C) 2001-2017 by RapidMiner and the contributors
*
* Complete list of developers available at our web site:
*
* http://rapidminer.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.
*
* TODO: remove class and transfer calls to com.rapidminer.tools.math.function.window.WindowFunction
*
* @author Ingo Mierswa
*/
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;
}
}
}