GaussWindow.java

/*
 *  Copyright (c) 2007 - 2008 by Damien Di Fede <ddf@compartmental.net>
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU Library 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 Library General Public License for more details.
 *
 *   You should have received a copy of the GNU Library General Public
 *   License along with this program; if not, write to the Free Software
 *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

package ddf.minim.analysis;

import ddf.minim.Minim;

/**
 * A Gauss window function.
 *
 * @author Damien Di Fede
 * @author Corban Brook
 * @see   <a href="http://en.wikipedia.org/wiki/Window_function#Gauss_windows">The Gauss Window</a>
 * 
 * @invisible
 */
public class GaussWindow extends WindowFunction
{
  double alpha;

  /** 
   * Constructs a Gauss window function. 
   * 
   * @param alpha
   * 		double: the alpha value to use for this window
   * */
  public GaussWindow(double alpha)
  {
    if (alpha < 0.0 || alpha > 0.5) 
    {
      Minim.error("Range for GaussWindow out of bounds. Value must be <= 0.5");
      return;
    }
    this.alpha = alpha;  
  }

  /** Constructs a Gauss window with a default alpha value of 0.25 */
  public GaussWindow()
  {
    this(0.25);
  }

  protected float value(int length, int index) 
  {
    return (float) Math.pow(Math.E, -0.5 * Math.pow((index - (length - 1) / (double) 2) / (this.alpha * (length - 1) / (double) 2), (double) 2));
  }
  
  public String toString()
  {
	  return "Gauss Window";
  }
}