package model.compute;


/**
 * <p>Title:Compute.java</p>
 * <p>Description: Does Basic computations to server other
 * analysis objects</p>
 * <p>Copyright: Copyright (c) 2009</p>
 * <p>Company: Hanover College</p>
 * @author John H. Krantz, Ph.D.
 * @version 0.1
 */

public class Compute {
	
	// empty constructor
	public Compute(){}
	
	/**
	 * does a correlation of two two dimensional arrays
	 * @param x first array
	 * @param y second array
	 * @return r the pearson's correlation value
	 */
	public static double Correl2D(double [][] x, double [][] y){
		double r = -2;
		
		if (x.length == y.length & 
				x[0].length == y[0].length){
			r = 0;
			// find the number of pairs
			double n_p = x.length*x[0].length;

			double numerator = 
				(n_p*sumXY2D(x,y)-(sum2D(x)*sum2D(y))); 
			
			double xDenom = n_p*sumSq2D(x)-square(sum2D(x));
			double yDenom = n_p*sumSq2D(y)-square(sum2D(y));
			
			r = numerator/
			       Math.sqrt(xDenom*yDenom);
		}
		
		return r;
	}
	
	/**
	 * Returns the square of a double values
	 * @param val
	 * @return double
	 */
	public static double square(double val){
		return val*val;
	}
	/**
	 * Returns the sum of a 2 dimensional array
	 * @param double [][] vals the array to be summed
	 * @return double the sum
	 */
	public static double sum2D(double [][] vals){
		double sum = 0;
		
		for (int i = 0; i < vals.length; i ++){
			for (int j = 0; j < vals[0].length; j ++){
				sum += vals[i][j];
			}
		}
		
		return sum;
	}
	/**
	 * Returns the sum of squares of a two dimensional array
	 * of values
	 * @param double [][] vals the array to be manipulated
	 * @return double the sum of squares of the array
	 */
	public static double sumSq2D(double [][] vals){
		double sumSq = 0;
		
		for (int i = 0; i < vals.length; i ++){
			for (int j = 0; j < vals[0].length; j ++){
				sumSq += square(vals[i][j]);
			}
		}
		
		return sumSq;
	}
	/**
	 * Gets the sum of x*y in 2d arrays,
	 * multiplies the values in the same positions in the
	 * two arrays and then sums.
	 * @param x
	 * @param y
	 * @return
	 */
	public static double sumXY2D(double [][] x, double [][] y){
		double sumXY = 0;
		
		if (x.length == y.length &
				x[0].length == y[0].length){
			for (int i = 0; i < x.length; i ++){
				for (int j = 0; j < y[0].length; j ++){
					sumXY += x[i][j]*y[i][j];
				}
			}
		}
				
		return sumXY;
	}
}