package fi.javasom.jsom;
/**
 * This is JSomMath class that contains mathematical functions for cooperative and adaptive processes.
 *
 *  Copyright (C) 2001  Tomi Suuronen
 *
 *  @version 1.0
 *
 *  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
*/

public class JSomMath
{
	private double[] cacheVector; //cache vector for temporary storage.
	private int sizeVector; //size of the cache vector.
	private double distCache; //distance cache.
	private double gaussianCache; //double cache for gaussian neighbourhood function operations.
	private int distCacheSize; //cache for the length of the two vectors.

	/**
	 * Constructor.
	 *
	 * @param int vectorSize - Size of a weight/input vector.
	*/
	public JSomMath(int vectorSize)
	{
		cacheVector = new double[vectorSize];
		for(int i=0;i<vectorSize;i++)
		{
			cacheVector[i] = 0.0;
		}
		sizeVector = cacheVector.length;
	}

	/**
	 * Calculates the Euclidean distance between two vectors.
	 *
	 * @param double[] x - 1st vector.
	 * @param double[] y - 2nd vector.
	 * @return double - returns the distance between two vectors, x and y
	*/
	public double getDistance(double[] x, double[] y)
	{
		distCache = 0.0;
		distCacheSize = x.length;
		for(int i=0;i<distCacheSize;i++)
		{
			distCache += Math.pow((x[i]-y[i]),2.0);
		}
		return Math.sqrt(distCache);
	}

	/**
	 * Calculates the exponential learning-rate parameter value.
	 *
	 * @param int n - current step (time).
	 * @param double a - initial value for learning-rate parameter (should be close to 0.1).
	 * @param int A - time constant (usually the number of iterations in the learning process).
	 * @return double - exponential learning-rate parameter value.
	*/
	public double expLRP(int n,double a,int A)
	{
		return (a * Math.exp(-1.0 * ((double)n) / ((double)A)));
	}

	/**
	 * Calculates the linear learning-rate parameter value.
	 *
	 * @param int n - current step (time).
	 * @param double a - initial value for learning-rate parameter (should be close to 0.1).
	 * @param int A - another constant (usually the number of iterations in the learning process).
	 * @return double - linear learning-rate parameter value.
	*/
	public double linLRP(int n,double a,int A)
	{
		return (a * (1 - ((double)n) / ((double)A)));
	}

	/**
	 * Calculates the inverse time learning-rate parameter value.
	 *
	 * @param int n - current step (time).
	 * @param double a - initial value for learning-rate parameter (should be close to 0.1).
	 * @param double A - another constant.
	 * @param double B - another constant.
	 * @return double - inverse time learning-rate parameter value.
	*/
	public double invLRP(int n,double a,double A,double B)
	{
		return (a * (A / (B + n)));
	}


	/**
	 * Calculates the gaussian neighbourhood width value.
	 *
	 * @param double g - initial width value of the neighbourhood.
	 * @param int n - current step (time).
	 * @param int t - time constant (usually the number of iterations in the learning process).
	 * @return double - adapted gaussian neighbourhood function value.
	*/
	public double gaussianWidth(double g,int n,int t)
	{
		return (g * Math.exp(-1.0 * ((double)n) / ((double)t)));
	}

	/**
	 * Calculates the Gaussian neighbourhood value.
	 *
	 * @param double[] i - winning neuron location in the lattice.
	 * @param double[] j - excited neuron location in the lattice.
	 * @param double width - width value of the neighbourhood.
	 * @return double - Gaussian neighbourhood value.
	*/
	private double gaussianNF(double[] i,double[] j, double width)
	{
		gaussianCache = getDistance(i,j);
		return (Math.exp(-1.0 * gaussianCache * gaussianCache / (2.0 * width * width)));
	}

	/**
	 * Calculates whether the excited neuron is in the Bubble neighbourhood set.
	 *
	 * @param double[] i - winning neuron location in the lattice.
	 * @param double[] j - excited neuron location in the lattice.
	 * @param double g - width value of the neighbourhood.
	 * @return boolean - true if located in the Bubble neighbourhood set.
	*/
	private boolean bubbleNF(double[] i,double[] j, double g)
	{
		if(getDistance(i,j) <= g)
		{
			return true;
		}
		return false;
	}

	/**
	 * Calculates the new adapted values for a weight vector, based on Bubble neighbourhood.
	 *
	 * @param double[] x - input vector.
	 * @param double[] w - weight vector.
	 * @param double[] i - winning neuron location in the lattice.
	 * @param double[] j - excited neuron location in the lattice.
	 * @param double g - adapted width value of the neighbourhood.
	 * @param double lrp - adapted learning-rate parameter value.
	 * @return double[] - Returns the adapted neuron values.
	*/
	public double[] bubbleAdaptation(double[] x,double[] w,double[] i,double[] j,double g,double lrp)
	{
		if(bubbleNF(i,j,g))
		{
			for(int k=0;k<sizeVector;k++)
			{
				cacheVector[k] = w[k] + lrp * (x[k] - w[k]);
			}
		}
		else
		{
			return w;
		}
		return cacheVector;
	}


	/**
	 * Calculates the new adapted values for a weight vector, based on Gaussian neighbourhood.
	 *
	 * @param double[] x - input vector.
	 * @param double[] w - weight vector.
	 * @param double[] i - winning neuron location in the lattice.
	 * @param double[] j - excited neuron location in the lattice.
	 * @param double width - adapted width value of the neighbourhood.
	 * @param double lrp - adapted learning-rate parameter value.
	 * @return double[] - Returns the adapted neuron values.
	*/
	public double[] gaussianAdaptation(double[] x,double[] w,double[] i,double[] j,double width,double lrp)
	{
		gaussianCache = gaussianNF(i,j,width);
		for(int k=0;k<sizeVector;k++)
		{
			cacheVector[k] = w[k] + lrp * gaussianCache * (x[k] - w[k]);
		}
		return cacheVector;
	}
}