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/*
 *   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 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 General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program.  If not, see .
 */

package weka.classifiers.neural.lvq.algorithm;

import weka.classifiers.neural.common.RandomWrapper;
import weka.classifiers.neural.common.learning.LearningRateKernel;
import weka.classifiers.neural.lvq.model.CodebookVector;
import weka.classifiers.neural.lvq.model.CommonModel;
import weka.classifiers.neural.lvq.model.LvqModel;
import weka.core.Instance;

/**
 * Description: Implementation of the LVQ2.1 algorithm. Makes use of a
 * window size to determine when the top 2 BMU's can be adjusted.
 * 
 * 

 * Copyright (c) Jason Brownlee 2004
 * 
 *
 * @author Jason Brownlee
 */
public class Lvq2_1Algorithm extends Lvq1Algorithm {

  protected final double windowSize;


  public Lvq2_1Algorithm(LearningRateKernel aLearningKernel,
			 CommonModel aModel,
			 RandomWrapper aRand,
			 double aWindow) {
    super(aLearningKernel, aModel, aRand);
    windowSize = aWindow;
  }


  /**
   * Responsbile for updating the model for the given data instance.
   * The top 2 BMU's are returned, and only updated if they are both in the same class
   * and the distance is within 1.0 the window size
   *
   * @param aInstance
   * @param lrate
   */
  protected void updateModel(Instance aInstance,
			     double lrate) {
    // get bmus
    CodebookVector[] bmus = ((LvqModel) model).get2Bmu(aInstance);

    // both bmu's must have different classes, one must have the correct
    // class and the distance ratio must be within the window
    if (bmusOfDifferentClassesAndInWindow(bmus[0], bmus[1], aInstance)) {
      // adjust the codebook vector
      updateVector(bmus[0], aInstance, lrate);
      updateVector(bmus[1], aInstance, lrate);
    }
  }

  /**
   * Checks that the two provided codebook vectors are of a different class,
   * and that one of them has the same class as the data instance. Also checks
   * that the ration of the vectors distance is within a defined window
   *
   * @param bmu1
   * @param bmu2
   * @param aInstance
   * @return
   */
  protected boolean bmusOfDifferentClassesAndInWindow(CodebookVector bmu1,
						      CodebookVector bmu2,
						      Instance aInstance) {
    // both bmu's must have different classes
    if (!isSameClass(bmu1, bmu2)) {
      // one of the bmu's classes must match the class of the instance
      if (isSameClass(aInstance, bmu1) || isSameClass(aInstance, bmu2)) {
	// min (di/dj, dj/di) > s, where s = (1-w)/(1+w)
	double distanceRatio = bmu1.getDistance() / bmu2.getDistance();
	double window = (1.0 - windowSize) / (1.0 + windowSize);

	// vectors must be within the window
	if (distanceRatio > window) {
	  return true;
	}
      }
    }

    return false;
  }
}