package umontreal.iro.lecuyer.randvar;
import umontreal.iro.lecuyer.rng.*;
import umontreal.iro.lecuyer.probdist.*;


/**
 * This class implements methods for generating random variates from the 
 * half-normal distribution with parameters μ and 
 * σ > 0.
 * Its density is
 * 
 * 

 * 

 * f (x) = ((2/π)1/2/σ)e-(x-μ)2/(2σ2),        for x > = μ,
 * 

 * 
 */
public class HalfNormalGen extends RandomVariateGen  {
    
   // Distribution parameters
   protected double mu;
   protected double sigma;



   /**
    * Creates a new half-normal generator with parameters μ = 
    *      mu and σ = sigma, using stream s.
    * 
    */
   public HalfNormalGen (RandomStream s, double mu, double sigma)  {
      super (s, new HalfNormalDist (mu, sigma));
      setParams (mu, sigma);
   }


   /**
    * Creates a new generator for the distribution dist,
    *      using stream s.
    * 
    */
   public HalfNormalGen (RandomStream s, HalfNormalDist dist)  {
      super (s, dist);
      if (dist != null)
         setParams (dist.getMu(), dist.getSigma());
   }


   /**
    * Generates a variate from the half-normal distribution with
    *  parameters μ = mu and σ = sigma, 
    * using stream s.
    * 
    * @param s the random stream
    * 
    *    @param mu the parameter mu
    * 
    *    @param sigma the parameter sigma
    * 
    *    @return Generates a variate from the HalfNormal distribution
    * 
    */
   public static double nextDouble (RandomStream s, double mu, double sigma) {
      return HalfNormalDist.inverseF (mu, sigma, s.nextDouble());
   }


   /**
    * Returns the parameter μ of this object.
    *   
    * @return the parameter mu
    * 
    */
   public double getMu() {
      return mu;
   }


   /**
    * Returns the parameter σ of this object.
    *   
    * @return the parameter mu
    * 
    */
   public double getSigma() {
      return sigma;
   }


   protected void setParams (double mu, double sigma) {
      if (sigma <= 0.0)
         throw new IllegalArgumentException ("sigma <= 0");
      this.mu = mu;
      this.sigma = sigma;
   }
}