package model.compute;

/**
 * <p>Title:NormalEQ.java</p>
 * <p>Description: Computes outputs using the normal distribution.
 * the primary distribution is 2D with one standard deviation so 
 * it is circular.</p>
 * <p>Copyright: Copyright (c) 2009</p>
 * <p>Company: Hanover College</p>
 * @author John H. Krantz, Ph.D.
 * @version 0.1
 */

public class NormalEq {
	
	// parameters
	private double meanX = 0;
	private double meanY = 0;
	private double sd = 1;
	
	// values
	private double x = 0;
	private double y = 0;
	
	// computational constants
	private final static double SQRT_2_PI 
				= Math.sqrt(2*Math.PI);

	// empty constrcutor
	public NormalEq(){}
	
	/**
	 * getNomral2D: get the height of a 2d normal distribution
	 * at a given location while setting all the parameters
	 * @param double mean_X mean of distribution in x dimension
	 * @param double mean_Y mean of distribution in y dimension
	 * @param double stdDev standard deviation of distribution
	 * @param double xPos x position of value to get
	 * @param double yPos y position of value to get
	 * @return double the height of the distribution at location
	 */
	public double getNormal2D(double mean_X,double mean_Y,
			double stdDev, double xPos, double yPos){
		
		setCtr(mean_X,mean_Y);
		setStdDev(stdDev);
		return getNormal2D(xPos,yPos);
	}
	/**
	 * getNormal2D: return the height of the 2d normal distribution
	 * with mean and standard deviation previously set.
	 * @param double xPos x position of value to get
	 * @param double yPos y position of value to get
	 * @return double height of the distribution at this location.
	 */
	public double getNormal2D(double xPos, double yPos){
		x = xPos;
		y = yPos;
		
		double val = 0;
		
		val = (1/(sd*SQRT_2_PI))*
		        Math.exp(-(sqr(x-meanX)+sqr(y-meanY))
		        		/(2*sqr(sd)));
		
		return val;
	}
	
	/**
	 * squares a number
	 * @param double val the number to square
	 * @return double
	 */
	private double sqr(double val){
		return val*val;
	}

	// set methods
	/**
	 * setCtr: set the center location of the 2d normal
	 * distribution
	 * @param double mean_X x position of the center.
	 * @param double mean_Y y position of the center.
	 */
	public void setCtr(double mean_X, double mean_Y){
		meanX = mean_X;
		meanY = mean_Y;
	}
	
	/**
	 * setStdDev: set the standard deviation of the normal
	 * distribution
	 * @param stdDev
	 */
	public void setStdDev(double stdDev){
		sd = stdDev > 0 ? stdDev : sd;
	}
}